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Sample records for hvdc wall bushing

  1. Online Partial Discharge Measurement of a High-voltage Direct Current Converter Wall-bushing%Online Partial Discharge Measurement of a High-voltage Direct Current Converter Wall-bushing

    Institute of Scientific and Technical Information of China (English)

    Nathan D. Jacob; William M. McDermid; Behzad Kordi

    2011-01-01

    An online partial discharge (PD) measurement performed on a high voltage direct current (HVDC) wall bushing successfully identified the presence of internal discharges. The wall bushing is a sulfur hexafluoride gas-insu- lated bushing, rated for 500 kV dc and terminated on a thyristor-controlled HVDC converter bridge. The measure- ment of PD within the HVDC station environment is particularly challenging due to the high levels of electromagnetic noise caused by thyristor switching events and external air-corona from the neighboring high-voltage equipment. An additional challenge is the "mixed" voltage stress on the bushing insulation, which has both ac and dc high-voltage components. There are also fast transients during the firing of thyristors in the HVDC conversion process that cause added stress to the insulation. As a result, the analysis and interpretation of PD data for HVDC equipment is more complex; PD pulses may occur in response to the ac, dc, or switching transient voltage stresses. In this paper, an on- line PD measurement strategy for noise filtering and isolation of PD sources within the bushing are discussed. The PD measurement data is plotted on a phase-resolved diagram where the line supply power cord voltage was used as a reference. The phase-resolved diagram appears to suggest that the fast transients, caused during switching, trigger some PD events. Measurements were also performed with the aid of a modern PD measurement instrument having noise separation capabilities. The findings from the online PD measurements are verified with physical evidence, found after the bushing was removed from service, suggested internal PD had occurred inside the bushing.

  2. The economic implications of bush encroachment and bush control ...

    African Journals Online (AJOL)

    The economic implications of bush encroachment and bush control in a weaner calf production ... Log in or Register to get access to full text downloads. ... Keywords: afrikaans; bush control; bush control cost; bush density; bush encroachment; ...

  3. System Design of HVDC Project

    Institute of Scientific and Technical Information of China (English)

    Ma Weimin; Yin Weiyang

    2011-01-01

    BackgroundHVDC transmission system is flexible,controllable,economic and environmentfriendly,which has compelling advantages in bulk long-distance power transfer and interconnection of power systems.Since the first HVDC project was put into commercial operation in Gotland in 1954,over 100 HVDC projects have been operating in the world.Currently,there are a number of HVDC projects under being upgraded,constructed or planed in Europe,North America,South America,Africa and Asia.

  4. Short Circuit Ratio analysis of multi-infeed HVDC system with a VSC-HVDC link

    DEFF Research Database (Denmark)

    Liu, Yan; Chen, Zhe

    2011-01-01

    As an important indicator of system stability, Short Circuit Ratio (SCR) is commonly used in power system analysis. For systems include HVDC link connection, the Effective SCR (ESCR) is mostly applied to indicate the strength of HVDC infeed bus. The contribution of VSC-HVDC link to multi......-infeed HVDC system stability has been analyzed a lot but the study on ESCR of this kind of system is still insufficient. This paper presents a calculation method for ESCR of the hybrid multi infeed HVDC system based on a simple two-infeed HVDC system model. The equivalent circuit of this system under short...

  5. Reidid Venemaale / Jason Bush

    Index Scriptorium Estoniae

    Bush, Jason

    2008-01-01

    Korruptsioonist Venemaal Samara piirkonnas, ettevõtte-vaenulikest ülevõtmiskatsetest ja riigiametnike osast selles, Venemaa presidendi algatusest korruptsiooni väljajuurimisel. Vt. samas Jason Bush. BP rasked ajad Venemaal

  6. HVDC power transmission technology assessment

    Energy Technology Data Exchange (ETDEWEB)

    Hauth, R.L.; Tatro, P.J.; Railing, B.D. [New England Power Service Co., Westborough, MA (United States); Johnson, B.K.; Stewart, J.R. [Power Technologies, Inc., Schenectady, NY (United States); Fink, J.L.

    1997-04-01

    The purpose of this study was to develop an assessment of the national utility system`s needs for electric transmission during the period 1995-2020 that could be met by future reduced-cost HVDC systems. The assessment was to include an economic evaluation of HVDC as a means for meeting those needs as well as a comparison with competing technologies such as ac transmission with and without Flexible AC Transmission System (FACTS) controllers. The role of force commutated dc converters was to be assumed where appropriate. The assessment begins by identifying the general needs for transmission in the U.S. in the context of a future deregulated power industry. The possible roles for direct current transmission are then postulated in terms of representative scenarios. A few of the scenarios are illustrated with the help of actual U.S. system examples. non-traditional applications as well as traditional applications such as long lines and asynchronous interconnections are discussed. The classical ``break-even distance`` concept for comparing HVDC and ac lines is used to assess the selected scenarios. The impact of reduced-cost converters is reflected in terms of the break-even distance. This report presents a comprehensive review of the functional benefits of HVDC transmission and updated cost data for both ac and dc system components. It also provides some provocative thoughts on how direct current transmission might be applied to better utilize and expand our nation`s increasingly stressed transmission assets.

  7. Power control method on VSC-HVDC in a hybrid multi-infeed HVDC system

    DEFF Research Database (Denmark)

    Liu, Yan; Chen, Zhe

    2012-01-01

    Multi-infeed HVDC (MIDC) system connected with VSC-HVDC links and LCC-HVDC links is a new structure in modern power systems, which can be called hybrid multi-infeed HVDC (HMIDC) system. The paper presents the voltage stability analysis of a HMIDC system modeled from a possible future Danish power...... stability of the system with induction machine loads. The proposed power control method based on a VSC power circle makes fully use of the VSC-HVDC capacity to support system voltage during fault situations. Simulation model of the studied HMIDC system is built in PSCAD. Simulation studies under different...

  8. Stability analysis of multi-infeed HVDC system applying VSC-HVDC

    DEFF Research Database (Denmark)

    Liu, Yan; Chen, Zhe

    2010-01-01

    on this model is analyzed under steady state and different kinds of grid fault transient situations. Two main control methods applied on VSC-HVDC link in this dual infeed HVDC system are investigated, and comparative analysis of them under transient situation is presented. A simulation model is built in PSCAD....../EMTDC to verify the theoretical analysis. Simulation results indicate that this dual infeed HVDC system can realize higher stability than single infeed HVDC system. And different control strategies on a VSC-HVDC link may result in different influence on AC voltage and active power oscillation during transient...... situation....

  9. DC Vs AC - War Of Currents For Future Power Systems A HVDC Technology Overview

    Directory of Open Access Journals (Sweden)

    Anil K. Rai

    2015-08-01

    Full Text Available DC vs AC discussion began in 1880s with development of first commercial power transmission in Wall Street New York. Later when AC technology came into notice by efforts of inventor and researcher Sir Nicola Tesla soon the advantages of AC transmission and AC devices overtook the DC technology. It was hoped that DC technology had lost battle of currents. Today with researches going on FACTS devices and bulk power transmission HVDC has again gained a reputation in power sector. Solution of this centuries old debate is to develop HVDC systems that assists HVAC systems for better performance stability and control

  10. Detection of Cracks in Aluminum Structure Beneath Inconel Repair Bushings

    Science.gov (United States)

    2008-04-01

    conductivity (i.e. Inconel 718 ) – Primary challenge then becomes detecting the weak eddy current field in the structure beyond the bushing wall...was able to be selected with inspectability as a goal. – Inconel 718 • low permeability (~μ0) • low conductivity (< 2% IACS) • Combined with...Detection of Cracks in Aluminum Structure beneath Inconel Repair Bushings Mr. Kenneth J. LaCivita (USAF) AFRL/RXSA Air Force Research Laboratory

  11. As Vitorias de Bush

    Directory of Open Access Journals (Sweden)

    Cristina Soreanu Pecequilo

    2011-08-01

    Full Text Available Considerando tanto a política internacional quanto a interna, o presente artigo busca expor algumas das maiores vitórias do presidente dos EUA George W. Bush e seus impactos para sua administração.

  12. Comparative study of superconducting fault current limiter both for LCC-HVDC and VSC-HVDC systems

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jong-Geon; Khan, Umer Amir; Lim, Sung-Woo; Shin, Woo-ju; Seo, In-Jin; Lee, Bang-Wook, E-mail: bangwook@hanyang.ac.kr

    2015-11-15

    Highlights: • The role of SFCL in types of HVDC system was evaluated. • A simulation model based on Korea Jeju–Haenam HVDC power system was designed in Matlab/Simulink. • Utilizing the designed both HVDC power system models, the efficiency of DC-SFCL was relatively low, compared to AC-SFCL. • It was deduced that the AC-SFCL was more effective in LCC-HVDC system than VSC-HVDC system. - Abstract: High Voltage Direct Current (HVDC) system has been evaluated as the optimum solution for the renewable energy transmission and long-distance power grid connections. In spite of the various advantages of HVDC system, it still has been regarded as an unreliable system compared to AC system due to its vulnerable characteristics on the power system fault. Furthermore, unlike AC system, optimum protection and switching device has not been fully developed yet. Therefore, in order to enhance the reliability of the HVDC systems mitigation of power system fault and reliable fault current limiting and switching devices should be developed. In this paper, in order to mitigate HVDC fault, both for Line Commutated Converter HVDC (LCC-HVDC) and Voltage Source Converter HVDC (VSC-HVDC) system, an application of resistive superconducting fault current limiter which has been known as optimum solution to cope with the power system fault was considered. Firstly, simulation models for two types of LCC-HVDC and VSC-HVDC system which has point to point connection model were developed. From the designed model, fault current characteristics of faulty condition were analyzed. Second, application of SFCL on each types of HVDC system and comparative study of modified fault current characteristics were analyzed. Consequently, it was deduced that an application of AC-SFCL on LCC-HVDC system with point to point connection was desirable solution to mitigate the fault current stresses and to prevent commutation failure in HVDC electric power system interconnected with AC grid.

  13. HVDC power transmission environmental issues review

    Energy Technology Data Exchange (ETDEWEB)

    Bailey, W.H.; Weil, D.E. [Bailey Research Associates, Inc., New York, NY (United States); Stewart, J.R. [Power Technologies, Inc., Schenectady, NY (United States)

    1997-04-01

    This report strives to define the various environmental effects associated with HVDC lines, discusses the current knowledge of their potential effects on biological and non-biological systems, and compares these effects associated with ac lines where appropriate.

  14. Bush telegraph readings in writing

    CERN Document Server

    Strongman, Luke

    2015-01-01

    A ""bush telegraph"" is an antipodean slang noun phrase for a ""grapevine"" or an informal network of communication. The title of this book on English language use comes from the fact that the book is written from the southern hemisphere (where the idea of a ""bush telegraph"" is more widely-known) and because the concept of a ""bush telegraph"" describes what the book provides - a discussion of salient points in English language use and tertiary teaching across branches of interrelated interests. Each chapter of Bush Telegraph describes aspects of English writing culture. Separately and toget

  15. HVDC System Characteristics and Simulation Models

    Energy Technology Data Exchange (ETDEWEB)

    Moon, S.I.; Han, B.M.; Jang, G.S. [Electric Enginnering and Science Research Institute, Seoul (Korea)

    2001-07-01

    This report deals with the AC-DC power system simulation method by PSS/E and EUROSTAG for the development of a strategy for the reliable operation of the Cheju-Haenam interconnected system. The simulation using both programs is performed to analyze HVDC simulation models. In addition, the control characteristics of the Cheju-Haenam HVDC system as well as Cheju AC system characteristics are described in this work. (author). 104 figs., 8 tabs.

  16. Comparative study of superconducting fault current limiter both for LCC-HVDC and VSC-HVDC systems

    Science.gov (United States)

    Lee, Jong-Geon; Khan, Umer Amir; Lim, Sung-Woo; Shin, Woo-ju; Seo, In-Jin; Lee, Bang-Wook

    2015-11-01

    High Voltage Direct Current (HVDC) system has been evaluated as the optimum solution for the renewable energy transmission and long-distance power grid connections. In spite of the various advantages of HVDC system, it still has been regarded as an unreliable system compared to AC system due to its vulnerable characteristics on the power system fault. Furthermore, unlike AC system, optimum protection and switching device has not been fully developed yet. Therefore, in order to enhance the reliability of the HVDC systems mitigation of power system fault and reliable fault current limiting and switching devices should be developed. In this paper, in order to mitigate HVDC fault, both for Line Commutated Converter HVDC (LCC-HVDC) and Voltage Source Converter HVDC (VSC-HVDC) system, an application of resistive superconducting fault current limiter which has been known as optimum solution to cope with the power system fault was considered. Firstly, simulation models for two types of LCC-HVDC and VSC-HVDC system which has point to point connection model were developed. From the designed model, fault current characteristics of faulty condition were analyzed. Second, application of SFCL on each types of HVDC system and comparative study of modified fault current characteristics were analyzed. Consequently, it was deduced that an application of AC-SFCL on LCC-HVDC system with point to point connection was desirable solution to mitigate the fault current stresses and to prevent commutation failure in HVDC electric power system interconnected with AC grid.

  17. Controller Architecture Design for MMC-HVDC

    Directory of Open Access Journals (Sweden)

    ZHANG, B.

    2014-05-01

    Full Text Available Compared with high voltage direct current (HVDC, the primary and secondary systems of modular multilevel converter based HVDC (MMC-HVDC are complicated. And the characteristics of the control system determine the properties of the MMC-HVDC system to a certain extent. This paper investigates the design of control architecture. First, the structure and parameters of the 21-level MMC-HVDC are designed. Second, the framework of the control system is studied in details and a complete control system is established. The communication mode and content are built between each layer, and the control system program is developed and debugged. Then The steady state test platform of the sub-module and the relevant control system are designed. Finally, the steady-state tests and the system test of the physical MMC-HVDC simulation system are conducted, which prove that the SMC can control the sub-module (SM efficiently, and the control system could realize efficient start and stop of the physical system. Meanwhile, the capacitor voltage balance between the sub-modules and the basic fault protection and control of the DC voltage and power are verified to be effective.

  18. New Progress on Self-Reliant Innovation of HVDC Technology

    Institute of Scientific and Technical Information of China (English)

    Li Yan; Li Xiaolin; Rao Hong; Zhao Jie; Yang Xiaoli

    2009-01-01

    @@ It is an important direction for China's power industry to master the design and the equipment manufacturing core technology of large-capacity HVDC power transmission systems,and to form the sustainable development capability.Before the self-reliant innovation of Guiguang Ⅱ HVDC project in 2004,the deficiency of the HVDC core technology in China was shown in the following aspects.

  19. Bush brossajet pertshatku / Jevgenija Garanzha

    Index Scriptorium Estoniae

    Garanža, Jevgenija, 1979-

    2003-01-01

    USA president George W. Bush esitas ultimaatumi Saddam Husseinile. Suurbritannia ministrid ei ole rahul Tony Blairi poliitikaga. ÜRO Julgeolekunõukogus ei hääletatud resolutsiooni Iraagi küsimuses

  20. Q&A Steve Bush

    Science.gov (United States)

    Bush, Steve

    2016-08-01

    Steve Bush, curriculum leader for science at Sackville School in West Sussex, was awarded the 2016 RAS Patrick Moore Medal for his contribution to astronomy education. But, as he explains here, it was only chance that led him to astronomy.

  1. Modeling of Pressure Effects in HVDC Cables

    DEFF Research Database (Denmark)

    Szabo, Peter; Hassager, Ole; Strøbech, Esben

    1999-01-01

    A model is developed for the prediction of pressure effects in HVDC mass impregnatedcables as a result of temperature changes.To test the model assumptions, experiments were performed in cable like geometries.It is concluded that the model may predict the formation of gas cavities....

  2. Present trends in HVDC converter station design

    Energy Technology Data Exchange (ETDEWEB)

    Carlsson, Lennart; Asplund, Gunnar; Bjorklund, Hans; Flisberg, Gunnar [ABB Power Systems AB, Ludvika (Sweden)

    1994-12-31

    HVDC converter station technology has developed rapidly to satisfy increasing requirements during past 10 - 15 years, but there has not been any dramatic changes since thyristor valves were introduced in the mid 70s. This paper describes some recent and expected future developments, that will substantiality change and simplify future converter stations. (author) 4 refs., 7 figs.

  3. HVDC grids for offshore and supergrid of the future

    CERN Document Server

    Gomis-Bellmunt, Oriol; Liang, Jun

    2016-01-01

    Presents the advantages, challenges, and technologies of High Voltage Direct Current (HVDC) Grids This book discusses HVDC grids based on multi-terminal voltage-source converters (VSC), which is suitable for the connection of offshore wind farms and a possible solution for a continent wide overlay grid. HVDC Grids: For Offshore and Supergrid of the Future begins by introducing and analyzing the motivations and energy policy drives for developing offshore grids and the European Supergrid. HVDC transmission technology and offshore equipment are described in the second part of the book. The third part of the book discusses how HVDC grids can be developed and integrated in the existing power system. The fourth part of the book focuses on HVDC grid integration, in studies, for different time domains of electric power systems. The book concludes by discussing developments of advanced control methods and control devices for enabling DC grids.

  4. Hybrid HVDC circuit breaker with self-powered gate drives

    OpenAIRE

    Effah, Francis Boafo; Watson, Alan James; Ji, Chao; Amankwah, Emmanuel K.; Johnson, Christopher Mark; Davidson, Colin; Clare, Jon C.

    2016-01-01

    The ever increasing electric power demand and the advent of renewable energy sources have revived the interest in high-voltage direct current (HVDC) multi-terminal networks. However, the absence of a suitable circuit breaker or fault tolerant VSC station topologies with the required characteristics (such as operating speed) have, until recently, been an obstacle in the development of large scale multi-terminal networks for HVDC. This paper presents a hybrid HVDC circuit breaker concept which...

  5. Hybrid HVDC circuit breaker with self-powered gate drives

    OpenAIRE

    Effah, Francis Boafo; Watson, Alan James; Ji, Chao; Amankwah, Emmanuel K.; Johnson, Christopher Mark; Davidson, Colin; Clare, Jon C.

    2016-01-01

    The ever increasing electric power demand and the advent of renewable energy sources have revived the interest in high-voltage direct current (HVDC) multi-terminal networks. However, the absence of a suitable circuit breaker or fault tolerant VSC station topologies with the required characteristics (such as operating speed) have, until recently, been an obstacle in the development of large scale multi-terminal networks for HVDC. This paper presents a hybrid HVDC circuit breaker concept which ...

  6. Modeling HVDC links in composite reliability evaluation: issues and solutions

    Energy Technology Data Exchange (ETDEWEB)

    Reis, Lineu B. de [Sao Paulo Univ., SP (Brazil). Escola Politecnica; Ramos, Dorel S. [Centrais Eletricas de Sao Paulo, SP (Brazil); Morozowski Filho, Marciano [Santa Catarina Univ., Florianopolis, SC (Brazil)

    1992-12-31

    This paper deals with theoretical and practical aspects of HVDC link modeling for composite (generation and transmission) system reliability evaluation purposes. The conceptual framework used in the analysis, as well as the practical aspects, are illustrated through an application example. Initially, two distinct HVDC link operation models are described: synchronous and asynchronous. An analysis of the most significant internal failure modes and their effects on HVDC link transmission capability is presented and a reliability model is proposed. Finally, a historical performance data of the Itaipu HVDC system is shown. 6 refs., 5 figs., 8 tabs.

  7. Bush and the Energy; Bush et l'energie

    Energy Technology Data Exchange (ETDEWEB)

    Mommaerts, C.; Barre, N.; Riche, P

    2001-07-01

    Facing the increase of the energy demand, Bush the President of the USA, decided to give a new impetus to the nuclear industry. These papers present the economic and the political analysis of this policy from the french point of view showing the anxiety facing the environmental impacts. (A.L.B.)

  8. Integration of CCC-HVDC and VSC-HVDC Systems to Supply an Island Network

    Directory of Open Access Journals (Sweden)

    G.B. Gharehpetian

    2013-05-01

    Full Text Available Acombination of Capacitor Commutated Converter (CCC HVDC and voltage source converter (VSC HVDC is proposed to supply an island system without any local generation. The key point of this integration is the flat characteristic of dc voltage of CCC-HVDC, which provides the condition for VSC to connect to CCC dc link via a current regulator. The advantages of proposed combined in feeding system are requiring only one dc line and having better dynamic responses. The structure of the proposed in feeding system as well as its control system is shown in this study. The simulation results are presented to confirm the effectiveness of the proposed system. Two other schemes for in feeding the passive island systems are studied to demonstrate the advantages of the proposed system.

  9. Redundancy Determination of HVDC MMC Modules

    Directory of Open Access Journals (Sweden)

    Chanki Kim

    2015-08-01

    Full Text Available An availability and a reliability prediction has been made for a high-voltage direct-current (HVDC module of VSC (Voltage Source Converter containing DC/DC converter, gate driver, capacitor and insulated gate bipolar transistors (IGBT. This prediction was made using published failure rates for the electronic equipment. The purpose of this prediction is to determinate the additional module redundancy of VSC and the used method is “binomial failure method”.

  10. Design and analysis of HVDC switch gear station for meshed HVDC grid

    OpenAIRE

    Serrano Jiménez, Patricia

    2013-01-01

    It is of fundamental interest to avoid faults in a DC grid due to the severely of these events. However, the faults are unavoidable, so in a fault case is necessary to act fast. The protection in a DC grid comprises a key component, the HVDC breaker. For this reason in this thesis, a simulation is programmed in order to be able to study the HVDC breaker operation, distinguishing between normal and fault operation. Matlab is the program used in this work, and an initial simulation is tested...

  11. Novel Fault Diagnosis Scheme for HVDC System via ESO

    Institute of Scientific and Technical Information of China (English)

    YAN Bing-yong; TIAN Zuo-hua; SHI Song-jiao

    2007-01-01

    A novel fault detection and identification (FDI) scheme for HVDC (High Voltage Direct Current Transmission) system was presented. It was based on the unique active disturbance rejection concept, where the HVDC system faults were estimated using an extended states observer (ESO). Firstly, the mathematical model of HVDC system was constructed, where the system states and disturbance were treated as an extended state. An augment HVDC system was established by using the extended state in rectify side and converter side, respectively. Then, a fault diagnosis filter was established to diagnose the HVDC system faults via the ESO theory. The evolution of the extended state in the augment HVDC system can reflect the actual system faults and disturbances, which can be used for the fault diagnosis purpose. A novel feature of this approach is that it can simultaneously detect and identify the shape and magnitude of the HVDC faults and disturbance. Finally, different kinds of HVDC faults were simulated to illustrate the feasibility and effectiveness of the proposed ESO based FDI approach. Compared with the neural network based or support vector machine based FDI approach, the ESO based FDI scheme can reduce the fault detection time dramatically and track the actual system fault accurately. What's more important, it needs not do complex online calculations and the training of neural network so that it can be applied into practice.

  12. Control of transformerless MMC-HVDC during asymmetric grid faults

    DEFF Research Database (Denmark)

    Timofejevs, Artjoms; Gamboa, Daniel; Liserre, Marco;

    2013-01-01

    Modular multilevel converter (MMC) is the latest converter topology suitable for the transformerless applications in HVDC transmission. HVDC systems are required to remain connected during grid faults, provide grid support and completely decouple the healthy side from the faulty one. The MMC...

  13. Review of VSC HVDC Connection for Offshore Wind Power Integration

    DEFF Research Database (Denmark)

    Korompili, Asimenia; Wu, Qiuwei; Zhao, Haoran

    2016-01-01

    system is limited due to surplus charging current of the cables. The VSC HVDC transmission system has the ability to overcome the limitation and offers other advantages over the HVAC transmission system. This paper is to review the VSC HVDC transmission technology and its application for offshore wind...

  14. Low voltage fault ride through control in MMC-HVDC

    DEFF Research Database (Denmark)

    Chaudhary, S.; Teodorescu, R.; Rizadis, D.

    2017-01-01

    Modular multilevel converters (MMCs) are the latest converter topology for the high voltage high power applications like the high voltage dc (HVDC) transmission. This paper presents the response of an MMC-HVDC converter during grid faults. Recent grid code requirements specify reactive current...

  15. Definition and Classification of Terms for HVDC Networks

    DEFF Research Database (Denmark)

    Vrana, Til Kristian; Bell, Keith; Sørensen, Poul Ejnar

    2015-01-01

    A systematic terminology for the field of HVDC networks has been developed, closing the gap between the well-established terminologies from AC power systems and HVDC technology. The most relevant items, topologies and concepts have been given clear and unique defined names, and these have been cl...

  16. An Improvement VSC-HVDC Station in Thailand

    Directory of Open Access Journals (Sweden)

    Narin Watanakul

    2014-12-01

    Full Text Available The paper was to study design and improvement voltage source converter (VSC based HVDC long-distance transmission system around 110km between Thailand to Malaysia with rated 300MVA (±300 kV. This paper presents an application of an asynchronous back to back VSC-HVDC system, which uses multilevel converter a 7- level Diode-Clamped SPWM converters topology technique for the realization of HVDC system. The controller has been proposed by using PQ control and feedforward decoupled current control algorithm. The design and experimentally controllers of VSC in lab scaled test, MATLAB/Simulink program were performed VSC-HVDC transmission system, simulation in order to evaluate transient performance, can be controlled independently under two phase to ground faulted and three phases to ground faulted conditions. The system are used as a guideline for analysing and design of the data process control with the PQ-control HVDC system.

  17. Complications of bush thoracotomy in the Highlands of Papua New Guinea.

    Science.gov (United States)

    Wallace, J; Tharion, J

    1995-03-01

    Bush thoracotomy is still practised in the South Western Highlands of Papua New Guinea, by traditional bush doctors. These bush thoracotomies are performed with the aim of letting out the 'bad blood' that is believed to have collected in the body cavities following injuries. During a 3 year period between 1989 and 1992, 183 patients with complications of bush thoracotomy were treated at the Sopas Hospital in the Highlands of Papua New Guinea. Of these patients, 55 had chest wall infections only, without any pleural involvement. Of the patients with empyemas, 14 were treated by decortication of the empyema with one death and all remaining patients were treated by drainage procedures with one death. We recommend early treatment by adequate drainage of the empyema and, where feasible, early decortication. Continuing education to eradicate the procedure, and provision of adequate surgical facilities for management of complications, should be the long-term aim for this continuing problem.

  18. Non-Pilot Protection of the HVDC Grid

    Science.gov (United States)

    Badrkhani Ajaei, Firouz

    This thesis develops a non-pilot protection system for the next generation power transmission system, the High-Voltage Direct Current (HVDC) grid. The HVDC grid protection system is required to be (i) adequately fast to prevent damages and/or converter blocking and (ii) reliable to minimize the impacts of faults. This study is mainly focused on the Modular Multilevel Converter (MMC) -based HVDC grid since the MMC is considered as the building block of the future HVDC systems. The studies reported in this thesis include (i) developing an enhanced equivalent model of the MMC to enable accurate representation of its DC-side fault response, (ii) developing a realistic HVDC-AC test system that includes a five-terminal MMC-based HVDC grid embedded in a large interconnected AC network, (iii) investigating the transient response of the developed test system to AC-side and DC-side disturbances in order to determine the HVDC grid protection requirements, (iv) investigating the fault surge propagation in the HVDC grid to determine the impacts of the DC-side fault location on the measured signals at each relay location, (v) designing a protection algorithm that detects and locates DC-side faults reliably and sufficiently fast to prevent relay malfunction and unnecessary blocking of the converters, and (vi) performing hardware-in-the-loop tests on the designed relay to verify its potential to be implemented in hardware. The results of the off-line time domain transients studies in the PSCAD software platform and the real-time hardware-in-the-loop tests using an enhanced version of the RTDS platform indicate that the developed HVDC grid relay meets all technical requirements including speed, dependability, security, selectivity, and robustness. Moreover, the developed protection algorithm does not impose considerable computational burden on the hardware.

  19. Research and development of HVDC remote control interface

    Science.gov (United States)

    Zhang, Zi-biao; Liu, Guo-ling; Geng, Zhan-xiao

    2013-03-01

    This paper introduces The development status quo of HVDC (high voltage direct current) power transmission project, analyzes the overall structure of RCI (remote control interface), puts forward the function design and the software realization. the communication message was accorded with the message defined in DL/T 634.5101-2002 / DL/T 634.5104-2002, the RCI could meet the requirement of the HVDC power transmission project ,which was approved, and there is guiding significance on the research of RCI of HVDC power transmission project..

  20. Grid connection of large offshore wind farms using HVDC

    Science.gov (United States)

    Xu, Lie; Andersen, Bjarne R.

    2006-07-01

    This article describes the use of high-voltage DC (HVDC) transmission systems for connection of large offshore wind farms using doubly fed induction generators (DFIGs) to the main grid. HVDC systems based on voltage source converters (VSC transmission) and on line-commutated converters (LCC HVDC) are discussed. The article describes proposed system configurations, operating principles and controls for the two technologies. PSCAD/EMTDC simulations are presented to demonstrate the robust performance of the proposed systems during variation of generation and onshore AC fault conditions. Copyright

  1. Transients in VSC-HVDC connected offshore wind power plant

    DEFF Research Database (Denmark)

    El-Khatib, Walid Ziad; Schwartzberg, D.; Arana Aristi, I.;

    2015-01-01

    The focus of this paper is transient phenomena in VSC-HVDC connected offshore wind power plants (WPPs). With the help of a case study modelled in PSCAD simulation software, energisation events are analysed in the time domain. A comparison with more well-known results obtained at energisation of AC...... connected WPPs indicates that significant differences arise as the energy involved in the switching event increases, due to the presence of the HVDC converter control. The influence of the offshore HVDC converter control gain in the most critical cases is assessed empirically and explained qualitatively....

  2. New Comparison of HVDC and HVAC Transmission system

    Directory of Open Access Journals (Sweden)

    Vahid Behravesh

    2012-06-01

    Full Text Available Alternating current (AC is the main driving force in the industries and residential areas, but for the long transmission line (more than 400 miles AC transmission is more expensive than that of direct current (DC. Technically, AC transmission line control is more complicated because of the frequency. DC transmission does not have these limitations, which has led to build long HVDC transmission lines over the last 40 years. HVDC technology made possible to transfer bulk power over long distances. This paper presents a comparative evaluation of HVDC and HVAC transmission systems .

  3. Site Selection for Hvdc Ground Electrodes

    Science.gov (United States)

    Freire, P. F.; Pereira, S. Y.

    2014-12-01

    High-Voltage Direct Current (HVDC) transmission systems are composed of a bipole transmission line with a converter substation at each end. Each substation may be equipped with a HVDC ground electrode, which is a wide area (up to 1 km Ø) and deep (from 3 to 100m) electrical grounding. When in normal operation, the ground electrode will dissipate in the soil the unbalance of the bipole (~1.5% of the rated current). When in monopolar operation with ground return, the HVDC electrode will inject in the soil the nominal pole continuous current, of about 2000 to 3000 Amperes, continuously for a period up to a few hours. HVDC ground electrodes site selection is a work based on extensive geophysical and geological surveys, in order to attend the desired design requirements established for the electrodes, considering both its operational conditions (maximum soil temperature, working life, local soil voltage gradients etc.) and the interference effects on the installations located up to 50 km away. This poster presents the geophysical investigations conducted primarily for the electrodes site selection, and subsequently for the development of the crust resistivity model, which will be used for the interference studies. A preliminary site selection is conducted, based on general geographical and geological criteria. Subsequently, the geology of each chosen area is surveyed in detail, by means of electromagnetic/electrical geophysical techniques, such as magnetotelluric (deep), TDEM (near-surface) and electroresistivity (shallow). Other complementary geologic and geotechnical surveys are conducted, such as wells drilling (for geotechnical characterization, measurement of the water table depth and water flow, and electromagnetic profiling), and soil and water sampling (for measurement of thermal parameters and evaluation of electrosmosis risk). The site evaluation is a dynamic process along the surveys, and some sites will be discarded. For the two or three final sites, the

  4. Vannevar Bush: Fifty Years Later

    Science.gov (United States)

    Lagowski, J. J.

    1995-12-01

    It is ironic that the 50th anniversary year of Vannevar Bush's Report to President Truman entitled "Science the Endless Frontier", which put into motion the eminently successful current system of education of scientists in this country occurs at a time when serious questions are being asked about the usefulness of that very system. Bush viewed his proposal to establish a national research foundation (later to be called the National Science Foundation) as a "social compact." Judgment of scientific merit would be delegated to expert peers in return for scientific progress, which would ultimately benefit the nation in terms of scientific needs--military security, economic productivity, and enhanced quality of life. Bush wanted the funding of basic research intertwined with training, and preferred to use universities for this purpose rather than industrial or national labs. Bush viewed college and university scientists as teachers and investigators. He believed university-based research would uniquely encourage and engage the next generation of scientists as no other institutional arrangement could. Bush did not trust industry's commitment to basic research, an instinct that proved prophetic. The academic reserve of scientists (PhD's in training and postdoctoral students) that existed before World War II, and upon which the United States could draw for its needs, which were primarily associated with defense efforts, was probably one of the defining factors in Bush's suggested strategy. Currently, that reserve of talent has gotten so large that it is the obvious throttle in the pipeline slowing the continued development of the university research enterprise. Since 1977, the rate at which we have trained new scientists exceeds an average of 4% annually. Since 1987, the "science work force"--PhD's--has grown at three times the rate of the general labor supply. Temporary positions for postdoctoral scientists have grown even faster (over 5% per year since 1989). To compound

  5. 一种新型的高压直流输电技术——MMC-HVDC%New HVDC power transmission technology:MMC-HVDC

    Institute of Scientific and Technical Information of China (English)

    韦延方; 卫志农; 孙国强; 郑玉平; 俞波

    2012-01-01

    The structure,operational principle and technical features of MMC-HVDC are described and the differences between MMC-HVDC and VSC-HVDC are compared. A brief survey is made on the present research statuses and engineering applications of MMC-HVDC. The drawbackes and some possible important trends of MMC-HVDC are analyzed,including:MMC-topology-related research,system design,fault protection, grounding,harmonics,loss,and so on. It is pointed out that the MMC-HVDC model for current research has low precision. For the limit of MMC topology,the mature control methods of VSC-HVDC can not be directly applied to MMC-HVDC. MMC-HVDC system has a strong ability of fault protection. Since current research emphasizes on the simulative analysis of fault protection,further research of MMC-HVDC protection strategy suitable for engineering applications is urgently needed. The implementation of grounding is difficult for high voltage capacitor banks are removed. For the large number of MMC sub-module,the better output voltage waveform is obtained when low switching frequency is used,and the system loss is low. The engineering practice of MMC-HVDC fit for China is discussed.%介绍了模块化多电平换流器型高压直流输电(MMC-HVDC)的基本结构,工作原理和技术特点,比较了MMC-HVDC相对于电压源换流器型高压直流输电(VSC-HVDC)的优势;对MMC-HVDC目前在国内外的研究进展和工程应用情况进行了回顾,分析了MMC-HVDC技术的不足之处和未来发展中可能的重点方向,包括主电路拓扑的相关问题研究、系统设计、故障保护、接地、谐波和损耗等,指出目前研究所采用的MMC-HVDC分析模型精度较低;因自身拓扑限制,目前成熟的VSC-HVDC控制方法无法直接用于MMC-HVDC; MMC-HVDC拥有较强的故障保护能力,当前研究着重于故障仿真分析,亟待探讨适合工程应用的保护策略;由于直流侧无需安装高压电容器组,MMC-HVDC接地实现困难;由于MMC-HVDC

  6. New Progress on Self-Reliant Innovation of HVDC Technology

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    It is an important direction for China's power industry to master the design and the equipment manufacturing core technology of large-capacity HVDC power transmission systems,and to form the sustainable development capability.

  7. A Flexible Power Control Method of VSC-HVDC Link for the Enhancement of Effective Short-Circuit Ratio in a Hybrid Multi-Infeed HVDC System

    DEFF Research Database (Denmark)

    Liu, Yan; Chen, Zhe

    2013-01-01

    With the emerging use of voltage source converter high voltage direct current (VSC-HVDC) links, the hybrid multi-infeed HVDC (HMIDC) system that includes the line commutated converter (LCC) HVDC and the VSC-HVDC links is becoming a promising power transmission structure in the modern power systems....... To evaluate the contribution of the VSC-HVDC link on the voltage stability of HMIDC system, this paper proposes an effective short circuit ratio (ESCR) calculation method. Through the calculation, the voltage support capability of the VSC-HVDC link can be quantitatively represented by the ESCR. Furthermore......, based on the calculation results, a flexible power control strategy for the VSC-HVDC link is developed to provide maximum reactive power support under grid faults. The theoretical analysis of the HMIDC system is based on the Danish transmission grid, evaluated through PSCAD simulations under different...

  8. Hybrid Models of Alternative Current Filter for Hvdc

    Directory of Open Access Journals (Sweden)

    Ufa Ruslan A.

    2017-01-01

    Full Text Available Based on a hybrid simulation concept of HVDC, the developed hybrid AC filter models, providing the sufficiently full and adequate modeling of all single continuous spectrum of quasi-steady-state and transient processes in the filter, are presented. The obtained results suggest that usage of the hybrid simulation approach is carried out a methodically accurate with guaranteed instrumental error solution of differential equation systems of mathematical models of HVDC.

  9. Control of Butterfly Bush with Postemergence Herbicides

    Science.gov (United States)

    Butterfly bush (Buddleja davidii) is classified as invasive in several parts of the United States. Two experiments were conducted to evaluate the effectiveness of four herbicides and two application methods on postemergence butterfly bush control. The four herbicides included: Roundup (glyphosate)...

  10. 33 CFR 117.547 - Bush River.

    Science.gov (United States)

    2010-07-01

    ... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Bush River. 117.547 Section 117.547 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY BRIDGES DRAWBRIDGE OPERATION REGULATIONS Specific Requirements Maryland § 117.547 Bush River. The draw of the Amtrak bridge...

  11. Optimizing the performance of a VSC HVDC control system

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Mau Cuong; Rudion, Krzystof; Styczynski, Zbigniew Antoni [Magdeburg Univ. (Germany). Chair for Electric Power Networks and Renewable Energy Sources

    2011-07-01

    This paper deals with the optimization of the parameters in the various control loops of a voltage source converter based high voltage direct current (VSC HVDC) transmission system connected to a doubly fed induction generator (DFIG) based wind farm. These control loops include a number of proportional-integral (PI) controllers. The performance of VSC HVDC depends on the parameters of these PI controllers. In this paper, the control strategy of each converter of the VSC HVDC is first introduced to investigate a VSC HVDC transmission system that transfers DFIG wind power over a long distance. Secondly, the optimization process, based on the simplex method which is proposed in the literature, is applied with the initial values of the PI controller's parameters, which are obtained by studying the classical frequency response of the open-loop transfer function of the VSC HVDC. The objective is to simultaneously minimize the weighted sum of the integral of the time absolute-error products (ITAE) of the AC voltage, reactive power, DC voltage and inner current controllers of both VSC stations. The effectiveness of the optimized parameters is assessed in the field of requirements of the VSC HVDC control system as mentioned above during voltage down to zero to reduce the generated power from wind farm. (orig.)

  12. Wind Farm Grid Integration Using VSC Based HVDC Transmission - An Overview

    DEFF Research Database (Denmark)

    Chaudhary, Sanjay Kumar; Teodorescu, Remus; Rodriguez, Pedro

    2008-01-01

    The paper gives an overview of HVAC and HVDC connection of wind farm to the grid, with an emphasis on Voltage Source Converter (VSC)-based HVDC for large wind farms requiring long distance cable connection. Flexible control capabilities of a VSC-based HVDC system enables smooth integration of wind...... farm into the power grid network while meeting the Grid Code Requirements (GCR). Operation of a wind farm with VSC-based HVDC connection is described....

  13. Dynamic Performance of an HVDC Link

    Directory of Open Access Journals (Sweden)

    S. A. ZIDI

    2005-09-01

    Full Text Available This paper presents the results of a simulation study on a 12 pulse HVDC (High Voltage Direct Current using a system in Matlab/Simulink. The object of the study is to investigate the steady state and dynamic performance of the system. First we examine response of current regulator after change in current reference in order to see the behavior of the controllers in controlling the desired current. Next, we present the digital simulation of a test system and show the response to a DC fault in the line and the AC fault at inverter side. The results are evaluated to enhance the recovery of the system from the disturbances for a full range of typical disturbances. The presented approach benefits from Simulink’s advantages in modeling and simulating dynamical systems.

  14. Assessment on the influence of resistive superconducting fault current limiter in VSC-HVDC system

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jong-Geon; Khan, Umer Amir; Hwang, Jae-Sang; Seong, Jae-Kyu; Shin, Woo-Ju; Park, Byung-Bae; Lee, Bang-Wook, E-mail: bangwook@hanyang.ac.kr

    2014-09-15

    Highlights: • The role of SFCLs in VSC-HVDC systems was evaluated. • Simulation model based on Korea Jeju-Haenam HVDC power system was designed. • An effect and the feasible locations of resistive SFCLs were evaluated. • DC line-to-line, DC line-to-ground and 3 phase AC faults were imposed and analyzed. - Abstract: Due to fewer risk of commutation failures, harmonic occurrences and reactive power consumptions, Voltage Source Converter (VSC) based HVDC system is known as the optimum solution of HVDC power system for the future power grid. However, the absence of suitable fault protection devices for HVDC system hinders the efficient VSC-HVDC power grid design. In order to enhance the reliability of the VSC-HVDC power grid against the fault current problems, the application of resistive Superconducting Fault Current Limiters (SFCLs) could be considered. Also, SFCLs could be applied to the VSC-HVDC system with integrated AC Power Systems in order to enhance the transient response and the robustness of the system. In this paper, in order to evaluate the role of SFCLs in VSC-HVDC systems and to determine the suitable position of SFCLs in VSC-HVDC power systems integrated with AC power System, a simulation model based on Korea Jeju-Haenam HVDC power system was designed in Matlab Simulink/SimPowerSystems. This designed model was composed of VSC-HVDC system connected with an AC microgrid. Utilizing the designed VSC-HVDC systems, the feasible locations of resistive SFCLs were evaluated when DC line-to-line, DC line-to-ground and three phase AC faults were occurred. Consequently, it was found that the simulation model was effective to evaluate the positive effects of resistive SFCLs for the effective suppression of fault currents in VSC-HVDC systems as well as in integrated AC Systems. Finally, the optimum locations of SFCLs in VSC-HVDC transmission systems were suggested based on the simulation results.

  15. Bush favours research at Pentagon and NIH

    CERN Multimedia

    MacIlwain, C

    2001-01-01

    The first budget from George W. Bush increases funding for military research and the NIH, while environmental work is drastically cut. The rest of civilian science funding is essentially frozen (1 page).

  16. Voltage sensitivity based reactive power control on VSC-HVDC in a wind farm connected hybrid multi-infeed HVDC system

    DEFF Research Database (Denmark)

    Liu, Yan; Chen, Zhe

    2013-01-01

    With increasing application of both Line Commutated Converter based High Voltage Direct Current (LCC-HVDC) systems and Voltage Source Converter based HVDC (VSC-HVDC) links, a new type of system structure named Hybrid Multi-Infeed HVDC (HMIDC) system is formed in the modern power systems. This paper...... presents the operation and control method of the wind farm connected HMIDC system. The wind power fluctuation takes large influence to the system voltages. In order to reduce the voltage fluctuation of LCC-HVDC infeed bus caused by the wind power variation, a voltage sensitivity-based reactive power...... control method is proposed in the paper. According to the calculated sensitivity factors, a reactive power increment is added in the control loop of VSC-HVDC so as to regulate the voltage of the target bus. Dynamic simulations in PSCAD/EMTDC and MATLAB are presented to assess the performance...

  17. Transient analysis of an HTS DC power cable with an HVDC system

    Science.gov (United States)

    Dinh, Minh-Chau; Ju, Chang-Hyeon; Kim, Jin-Geun; Park, Minwon; Yu, In-Keun; Yang, Byeongmo

    2013-11-01

    The operational characteristics of a superconducting DC power cable connected to a highvoltage direct current (HVDC) system are mainly concerned with the HVDC control and protection system. To confirm how the cable operates with the HVDC system, verifications using simulation tools are needed. This paper presents a transient analysis of a high temperature superconducting (HTS) DC power cable in connection with an HVDC system. The study was conducted via the simulation of the HVDC system and a developed model of the HTS DC power cable using a real time digital simulator (RTDS). The simulation was performed with some cases of short circuits that may have caused system damage. The simulation results show that during the faults, the quench did not happen with the HTS DC power cable because the HVDC controller reduced some degree of the fault current. These results could provide useful data for the protection design of a practical HVDC and HTS DC power cable system.

  18. wall

    Directory of Open Access Journals (Sweden)

    Irshad Kashif

    2016-01-01

    Full Text Available Maintaining indoor climatic conditions of buildings compatible with the occupant comfort by consuming minimum energy, especially in a tropical climate becomes a challenging problem for researchers. This paper aims to investigate this problem by evaluating the effect of different kind of Photovoltaic Trombe wall system (PV-TW on thermal comfort, energy consumption and CO2 emission. A detailed simulation model of a single room building integrated with PV-TW was modelled using TRNSYS software. Results show that 14-35% PMV index and 26-38% PPD index reduces as system shifted from SPV-TW to DGPV-TW as compared to normal buildings. Thermal comfort indexes (PMV and PPD lie in the recommended range of ASHARE for both DPV-TW and DGPV-TW except for the few months when RH%, solar radiation intensity and ambient temperature were high. Moreover PVTW system significantly reduces energy consumption and CO2 emission of the building and also 2-4.8 °C of temperature differences between indoor and outdoor climate of building was examined.

  19. Transmission of Power to the Island Using HVDC

    Directory of Open Access Journals (Sweden)

    B. Vijayalakshmi

    2012-09-01

    Full Text Available HVDC transmission is more effective andeconomically cheaper where bulk power is to betransmitted over long distance. Hence the surpluspower from a remote place can be exported to theneedy place at cheaper rate. The HVDC systemrequire only one transmission wire and the groundreturn or seawater can be used as an another line.The Lakshadweep Island is located at faraway placefrom the northeast part of India where the surpluspower is available. The seawater for return path isavailable. The diesel for D.G set is transported fromIndian mainland through ship where lot of economyis lost only for transportation. In this paper thetransmission of HVDC from Indian mainland toLakshadweep is analyzed at economically cheaperrate.

  20. Optimisation of VSC-HVDC Transmission for Wind Power Plants

    DEFF Research Database (Denmark)

    Silva, Rodrigo Da

    Connection of Wind Power Plants (WPP), typically oshore, using VSCHVDC transmission is an emerging solution with many benefits compared to the traditional AC solution, especially concerning the impact on control architecture of the wind farms and the grid. The VSC-HVDC solution is likely to meet...... more stringent grid codes than a conventional AC transmission connection. The purpose of this project is to analyse how HVDC solution, considering the voltage-source converter based technology, for grid connection of large wind power plants can be designed and optimised. By optimisation, the project...... the requirements established by the operators in the multiterminal VSC-HVDC transmission system. Moreover, the possibility in minimising the overall transmission losses can be a solution for small grids and the minimisation in the dispatch error is a new solution for power deliver maximisation. The second study...

  1. Technology Goes Bush: Using Mobile Technologies to Support Learning in a Bush Kinder Program

    Science.gov (United States)

    Masters, Jennifer; Grogan, Leanne

    2015-01-01

    A "bush kinder" is the Australian equivalent of a European forest kindergarten. Although it is not usual for technology to be used in the type of program, the authors suggest that mobile technologies can be used creatively and sensitively to support learning in the bush kinder context. This paper describes an ethnographical case study…

  2. Stability of DC Voltage Droop Controllers in VSC HVDC Systems

    DEFF Research Database (Denmark)

    Thams, Florian; Suul, Jon Are; D’Arco, Salvatore;

    2015-01-01

    Future multi-terminal HVDC systems are expected to utilize dc voltage droop controllers and several control implementations have been proposed in literature. This paper first classifies possible dc droop implementations in a simple framework. Then, the small-signal stability of a VSC-based conver......Future multi-terminal HVDC systems are expected to utilize dc voltage droop controllers and several control implementations have been proposed in literature. This paper first classifies possible dc droop implementations in a simple framework. Then, the small-signal stability of a VSC...

  3. Advanced solutions in power systems HVDC, facts, and artificial intelligence

    CERN Document Server

    Liu, Chen-Ching; Edris, Abdel-Aty

    2016-01-01

    Provides insight on both classical means and new trends in the application of power electronic and artificial intelligence techniques in power system operation and control This book presents advanced solutions for power system controllability improvement, transmission capability enhancement and operation planning. The book is organized into three parts. The first part describes the CSC-HVDC and VSC-HVDC technologies, the second part presents the FACTS devices, and the third part refers to the artificial intelligence techniques. All technologies and tools approached in this book are essential for power system development to comply with the smart grid requirements.

  4. The impact of HVDC innovations on the power industry

    OpenAIRE

    Stenberg, Nikolaos

    2013-01-01

    The purpose of this thesis is to examine the potential impact of High Voltage Direct Current (HVDC) innovations on the power industry. A short historical review is provided on the so-called ‘War of the Currents’, which has placed alternating current (AC) as the dominant platform for power transmission. The revival of DC in high voltage transmission is here examined as a reverse salient, as various indicators show that the role of HVDC in the power industry seems to be constantly growing. In t...

  5. The impact of HVDC innovations on the power industry

    OpenAIRE

    Stenberg, Nikolaos

    2013-01-01

    The purpose of this thesis is to examine the potential impact of High Voltage Direct Current (HVDC) innovations on the power industry. A short historical review is provided on the so-called ‘War of the Currents’, which has placed alternating current (AC) as the dominant platform for power transmission. The revival of DC in high voltage transmission is here examined as a reverse salient, as various indicators show that the role of HVDC in the power industry seems to be constantly growing. In t...

  6. DESIGN OF A BUSH PRESSING MACHINE FOR PUMPS

    Directory of Open Access Journals (Sweden)

    AMITH KALEKAR

    2015-03-01

    Full Text Available Bearings are among the most important components in the vast majority of machines. Bush is an independent plain bearing that is inserted into a housing to provide a bearing surface for rotary applications. Bushes are fitted either by pressing for less interference or by heating the frame or cooling the bushes using dry ice or liquid nitrogen. In the present case, due to uneven cooling using liquid nitrogen or other problems, bush is not fitting easily in some of the pump frames. So there is a need of a bush pressing machine. A ‘C’ frame type hydraulic bush pressing machine is designed in this work.

  7. Assessment on the influence of resistive superconducting fault current limiter in VSC-HVDC system

    Science.gov (United States)

    Lee, Jong-Geon; Khan, Umer Amir; Hwang, Jae-Sang; Seong, Jae-Kyu; Shin, Woo-Ju; Park, Byung-Bae; Lee, Bang-Wook

    2014-09-01

    Due to fewer risk of commutation failures, harmonic occurrences and reactive power consumptions, Voltage Source Converter (VSC) based HVDC system is known as the optimum solution of HVDC power system for the future power grid. However, the absence of suitable fault protection devices for HVDC system hinders the efficient VSC-HVDC power grid design. In order to enhance the reliability of the VSC-HVDC power grid against the fault current problems, the application of resistive Superconducting Fault Current Limiters (SFCLs) could be considered. Also, SFCLs could be applied to the VSC-HVDC system with integrated AC Power Systems in order to enhance the transient response and the robustness of the system. In this paper, in order to evaluate the role of SFCLs in VSC-HVDC systems and to determine the suitable position of SFCLs in VSC-HVDC power systems integrated with AC power System, a simulation model based on Korea Jeju-Haenam HVDC power system was designed in Matlab Simulink/SimPowerSystems. This designed model was composed of VSC-HVDC system connected with an AC microgrid. Utilizing the designed VSC-HVDC systems, the feasible locations of resistive SFCLs were evaluated when DC line-to-line, DC line-to-ground and three phase AC faults were occurred. Consequently, it was found that the simulation model was effective to evaluate the positive effects of resistive SFCLs for the effective suppression of fault currents in VSC-HVDC systems as well as in integrated AC Systems. Finally, the optimum locations of SFCLs in VSC-HVDC transmission systems were suggested based on the simulation results.

  8. Electrical bushing for a superconductor element

    Science.gov (United States)

    Mirebeau, Pierre; Lallouet, Nicolas; Delplace, Sebastien; Lapierre, Regis

    2010-05-04

    The invention relates to an electrical bushing serving to make a connection at ambient temperature to a superconductor element situated in an enclosure at cryogenic temperature. The electrical bushing passes successively through an enclosure at intermediate temperature between ambient temperature and cryogenic temperature, and an enclosure at ambient temperature, and it comprises a central electrical conductor surrounded by an electrically insulating sheath. According to the invention, an electrically conductive screen connected to ground potential surrounds the insulating sheath over a section that extends from the end of the bushing that is in contact with the enclosure at cryogenic temperature at least as far as the junction between the enclosure at intermediate temperature and the enclosure at ambient temperature. The invention is more particularly applicable to making a connection to a superconductor cable.

  9. Grid Integration of Large PV Power Systems Using HVDC Link

    Directory of Open Access Journals (Sweden)

    Gamal Sowilam

    2016-09-01

    Full Text Available This paper explores the interconnection of large scale Photo-Voltaic (PV systems to the grid though a High Voltage Direct Current (HVDC link. HVDC link is recently utilized for transmission lines longer than 50 km. It is usually utilized to interconnect two asynchronous grids with the same or different frequencies while avoiding stability disturbances greatly. A suitable Maximum Power Point Tracking (MPPT techniques is employed to control the performance of the integrated PV system. The system of the HVDC link has two 12-pulse converter using thyristor-bridges. The delay and the extinction angles at the rectifier and the inverter units control the flow and the quantity of the transmitted power from the PV system into the grid. Fixed capacitors and filters are used to provide the AC side with the required reactive power and reduce the harmonic contents. For evaluation purposes, different simulation investigations are carried out with a detailed modeling using the MATLAB. These tests corroborate the efficacy of HVDC link for integrating large PV systems to electrical grids.

  10. Control strategies for VSC-based HVDC transmission system

    DEFF Research Database (Denmark)

    Stan, Ana-Irina; Stroe, Daniel Ioan; Silva, Rodrigo Da

    2011-01-01

    the behavior of the developed VSC-based HVDC transmission system two study cases are carried out using MATLAB/Simulink. The results obtained from simulations show acceptable performances, of the proposed strategies, when changes in the reference parameters are considered. The active power flow between...

  11. The New Breakthrough in Technical Standards for HVDC Transmission Equipments

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    Project Name:12 Standards including GB/T 20838-2007 Technical Parameters and Requirements for HVDC Oil Immersed Convector Transformer Main Participant Units:Economic Research Institute,Xi'an High Voltage Apparatus Research Institute Co.Ltd.,Shenyang Transformer Academy,Xi'an Power Electronics Research Institute,China Electric Power Research Institute,TBEA Shenyang Transformer Group Corporation,China Southern Power Grid Technology Research Center Main Contributors:Fang Xiaoyan,Gou Ruifeng,Zhang Zhonguo,Yu Hongqi,Wang Mingxin,Mi Chuanlong,Wang Jian,Rao Hong,Guo Liping,Liu Jing Award Grade:First Prize Backg round High Voltage Direct Current Transmission (HVDC) is an important means to address issues of high voltage,high power,long distance and asynchronous grid-connection,and has been listed in the national mid-term and long-term science and technology development plan.The world-famous Three Gorges Project (TGP) was designed to use HVDC technology in two-thirds of electric power transmission according to the TGP plan.So it is of significance to develop HVDC in China for improvement of transmission capacity and quality.

  12. Bush's Second-term Foreign Strategy

    Institute of Scientific and Technical Information of China (English)

    Task Force on U.S. Foreign Strategic Review

    2006-01-01

    @@ In 2005, the first year of Bush's second term, the U.S. global strategy entered a new era of adjustment and intensification after four years' practice. As Bush won his reelection with an overwhelming advantage, he was so ambitious that his mind was preoccupied with desire of leaving political and diplomatic heritage to the future. However, a series of challenges and problems popped up and forced him to adapt his foreign strategy to the rapidly changing domestic and international environment. His foreign strategy, ranging from its priorities, means to style, has experienced changes with stronger conservative and realistic flavor.

  13. Dynamic Performance of a Back-to-Back HVDC Station Based on Voltage Source Converters

    Science.gov (United States)

    Khatir, Mohamed; Zidi, Sid-Ahmed; Hadjeri, Samir; Fellah, Mohammed-Karim

    2010-01-01

    The recent developments in semiconductors and control equipment have made the voltage source converter based high voltage direct current (VSC-HVDC) feasible. This new DC transmission is known as "HVDC Light or "HVDC Plus by leading vendors. Due to the use of VSC technology and pulse width modulation (PWM) the VSC-HVDC has a number of potential advantages as compared with classic HVDC. In this paper, the scenario of back-to-back VSC-HVDC link connecting two adjacent asynchronous AC networks is studied. Control strategy is implemented and its dynamic performances during disturbances are investigated in MATLAB/Simulink program. The simulation results have shown good performance of the proposed system under balanced and unbalanced fault conditions.

  14. Study on VSC HVDC Modeling and Control Strategies for Wind Power Integration

    DEFF Research Database (Denmark)

    Korompili, Asimenia; Wu, Qiuwei

    in their applications. The main focus is given in the HVDC transmission systems, since they do not exhibit these disadvantages, whereas they additionally present beneficial attributes. This is the reason for which the applications of HVDC systems have been increased in the latest years. A brief description of different...... application cases is provided in the introduction of this report, while the rest chapters deal with the use of the HVDC technology for the grid connection of offshore wind farms. The main structure of the HVDC system is analysed, by describing the role and operation of its main components. Especially...... is performed, regarding power losses, costs, equipment aspects and control capabilities. It is concluded that the VSC-HVDC system exhibits the most advantageous features for the grid connection of offshore wind farms. In addition, various topologies of the HVDC converter stations are analysed. Furthermore...

  15. HVDC Ground Electrodes - a Source of Geophysical Data

    Science.gov (United States)

    Freire, P. F.; Pereira, S. Y.

    2015-12-01

    The HVDC electrode is a component of a High Voltage Direct Current energy transmission system, and is designed to inject into the ground continuous currents up to 3500 A. The typical HVDC ground electrode is a ring of vertical conductors, 1 km wide, buried a few tens of meters.The design of a HVDC electrode is based on extensive geological, geotechnical and geophysical surveys. Geophysical data are usually electrical (VES) and electromagnetic (TEM/MT) acquisitions, for the modeling of the shallow, near-surface and deep layers of the crust. This survey aims, first, the electrode site selection, and then, at the selected site, this data is combined into a single apparent resistivity curve, which is inverted, allowing for the determination of the layered geoelectric crust model. The injection of electrical continuous current in the electrode is then simulated, with the geoelectric crust model, for the determination of the soil surface potential profile (which is usually asymmetric for different directions, due to non-1D geoelectric models).For the commissioning of a HVDC electrode, field measurements are done, such as electrode grounding resistance, soil surface potentials and metal-to-soil potentials at specific structures (buried pipelines, for instance).The geophysical data acquired during the design phase is a set of data completely independent from the electrical data acquired during the electrode commissioning phase, and both are correlated by the geoelectric model. It happens, therefore, that the geoelectric model can be calibrated based on the electrical data, with the correction of static shifts and other adjustments.This paper suggests that the commissioning of HVDC systems should be associated to a research & development program, with a university or foundation. The idea is to enjoy the opportunity of a more complete field survey, with the acquisition of a wide set of data for a better geological characterization of the area where the electrode was built.

  16. Statistics and Analysis on Reliability of HVDC Transmission Systems of SGCC

    Institute of Scientific and Technical Information of China (English)

    Xu

    2010-01-01

    Reliability level of HVDC power transmission systems becomes an important factor impacting the entire power grid. The author analyzes the reliability of HVDC power transmission systems owned by SGCC since 2003 in respect of forced outage times, forced energy unavailability, scheduled energy unavailability and energy utilization efficiency. The results show that the reliability level of HVDC power transmission systems owned by SGCC is improving. By analyzing different reliability indices of HVDC power transmission system, the maximum asset benefits of power grid can be achieved through building a scientific and reasonable reliability evaluation system.

  17. Coordinated frequency regulation by offshore wind farms and VSC-HVDC transmission

    DEFF Research Database (Denmark)

    Liu, Hongzhi; Chen, Zhe

    2014-01-01

    With the increasing wind penetration, large-scale offshore wind farms exert significant impact on power system security and operation, and thus are required to contribute to system frequency regulation. This paper develops a coordinated control strategy for offshore wind farms with voltage source...... converter-based HVDC (VSC-HVDC) transmission system to participate in power system frequency regulation. The strategy explores the frequency support capability of offshore wind farms and VSC-HVDC. By implementing the proposed coordinated control, the VSCHVDC link is able to provide quick virtual inertial...... are presented to demonstrate the frequency regulation capability of VSC-HVDC and validate the effectiveness of the proposed coordinated control strategy....

  18. Environmental Assessment Colonial Seabird Management on Two Bush Island and Little Two Bush Island, Maine

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This is an environmental assessment that discussed and analyzes the proposed restoration of historical nesting populations of Common and Roseate terns on Two Bush...

  19. President Bush ei kuula esindajatekoda / Tõnis Erilaid

    Index Scriptorium Estoniae

    Erilaid, Tõnis, 1943-

    2007-01-01

    USA kongressi esindajatekoda hääletas juba kolmas kord selle poolt, et hiljemalt nelja kuu pärast hakataks vähendama vägesid Iraagis, samas on president George W. Bush Iraagi sõja suhtes optimistlikult meelestatud ning paneb tõenäoliselt ka sel korral seaduseelnõule veto. Lisa: Iraagis on langenud 3610 ameeriklast

  20. Evaluating the Bush Climate Change Initiative

    NARCIS (Netherlands)

    Moor APG de; Berk MM; Elzen MGJ den; Vuuren DP van; MNV

    2002-01-01

    This report evaluates the Climate Change Initiative as presented by President Bush on February 14, 2002. The President's proposal aims to reduce the greenhouse gas intensity of the US economy by 18 per cent between 2002 and 2012. This policy target can be regarded as being very modest, when compared

  1. Evaluating the Bush Climate Change Initiative

    NARCIS (Netherlands)

    Moor APG de; Berk MM; Elzen MGJ den; Vuuren DP van; MNV

    2002-01-01

    Deze rapportage evalueert het Climate Change Initiative dat President Bush op 14 februari 2002 heeft gepresenteerd. Dit Initiatief beoogt de broeikasgasintensiteit van de Amerikaanse economie tussen 2002 en 2012 met 18 procent te verminderen. Deze beleidsambitie valt als zeer bescheiden te typer

  2. Bush and Gore Focus on Schools.

    Science.gov (United States)

    Joiner, Lottie L.

    2000-01-01

    In the 2000 presidential race, education seems a top priority for Vice-President Al Gore and Texas Governor George W. Bush. Although both candidates are promising billions of federal-aid dollars to raise standards, many believe they are ignoring factors such as student motivation and funding inequities. (MLH)

  3. Bush skazal ne sovsem to, tshto skazal

    Index Scriptorium Estoniae

    2006-01-01

    USA abivälisminister Euroopa ja Euraasia küsimustes Daniel Fried teatas, et NATO riigid toetavad Gruusia, Moldova ja Aserbaidžaani territoriaalset terviklikkust, kuid ei luba neil seda taastada relva abil. Abiminister selgitab, mida pidas USA president George W. Bush silmas, kui ta avaldas Riia tippkohtumisel toetust Gruusiale tema püüdlustes liituda NATO-ga

  4. Bush skazal ne sovsem to, tshto skazal

    Index Scriptorium Estoniae

    2006-01-01

    USA abivälisminister Euroopa ja Euraasia küsimustes Daniel Fried teatas, et NATO riigid toetavad Gruusia, Moldova ja Aserbaidžaani territoriaalset terviklikkust, kuid ei luba neil seda taastada relva abil. Abiminister selgitab, mida pidas USA president George W. Bush silmas, kui ta avaldas Riia tippkohtumisel toetust Gruusiale tema püüdlustes liituda NATO-ga

  5. The Invasive Buddleja Daviddi (Butterfly Bush)

    Science.gov (United States)

    Buddleja davidii Franchet (Synonym. Buddleia davidii; common name butterfly bush) is a perennial, semi-deciduous, multi-stemmed shrub that is resident in gardens and disturbed areas. Since its introduction to the United Kingdom from China in the late 1800s, B. davidii has become...

  6. Experimental validation of prototype high voltage bushing

    Science.gov (United States)

    Shah, Sejal; Tyagi, H.; Sharma, D.; Parmar, D.; M. N., Vishnudev; Joshi, K.; Patel, K.; Yadav, A.; Patel, R.; Bandyopadhyay, M.; Rotti, C.; Chakraborty, A.

    2017-08-01

    Prototype High voltage bushing (PHVB) is a scaled down configuration of DNB High Voltage Bushing (HVB) of ITER. It is designed for operation at 50 kV DC to ensure operational performance and thereby confirming the design configuration of DNB HVB. Two concentric insulators viz. Ceramic and Fiber reinforced polymer (FRP) rings are used as double layered vacuum boundary for 50 kV isolation between grounded and high voltage flanges. Stress shields are designed for smooth electric field distribution. During ceramic to Kovar brazing, spilling cannot be controlled which may lead to high localized electrostatic stress. To understand spilling phenomenon and precise stress calculation, quantitative analysis was performed using Scanning Electron Microscopy (SEM) of brazed sample and similar configuration modeled while performing the Finite Element (FE) analysis. FE analysis of PHVB is performed to find out electrical stresses on different areas of PHVB and are maintained similar to DNB HV Bushing. With this configuration, the experiment is performed considering ITER like vacuum and electrical parameters. Initial HV test is performed by temporary vacuum sealing arrangements using gaskets/O-rings at both ends in order to achieve desired vacuum and keep the system maintainable. During validation test, 50 kV voltage withstand is performed for one hour. Voltage withstand test for 60 kV DC (20% higher rated voltage) have also been performed without any breakdown. Successful operation of PHVB confirms the design of DNB HV Bushing. In this paper, configuration of PHVB with experimental validation data is presented.

  7. Generic Models of Wind Turbine Generators for Advanced Applications in a VSC-based Offshore HVDC Network

    DEFF Research Database (Denmark)

    Zeni, Lorenzo; Margaris, Ioannis; Hansen, Anca Daniela;

    This paper focuses on generic Type 4 wind turbine generators models, their applicability in modern HVDC connections and their capability to provide advanced ancillary services therefrom. A point-to-point HVDC offshore connection is considered. Issues concerning coordinated HVDC and wind farm...... involving the HVDC converters- The performance against frequency disturbances of the two presented configurations is assessed and discussed by means of simulations....

  8. Development of a compact bushing for NBI

    Science.gov (United States)

    de Esch, H. P. L.; Simonin, A.; Grand, C.; Lepetit, B.; Lemoine, D.; Márquez-Mijares, M.; Minea, T.; Caillault, L.; Seznec, B.; Jager, T.; Odic, E.; Kirkpatrick, M. J.; Teste, Ph.; Dessante, Ph.; Almaksour, K.

    2017-08-01

    Research into a novel type of compact bushing is being conducted through the HVIV (High Voltage holding In Vacuum) partnership between CEA-Cadarache1, GeePs-Centralesupélec4, LPGP3 and LCAR2. The bushing aims to concentrate the high electric field inside its interior, rather than in the vacuum tank. Hence the field emission current is also concentrated inside the bushing and it can be attempted to suppress this so-called dark current by conditioning the internal surfaces and by adding gas. LCAR have performed theoretical quantum mechanical studies of electron field emission and the role of adsorbates in changing the work function. LPGP studied the ionization of gas due to field emission current and the behavior of micro particles exposed to emissive electron current in the vacuum gap under high electric fields. Experiments at Geeps have clarified the role of surface conditioning in reducing the dark current. Geeps also found that adding low pressure nitrogen gas to the vacuum is much more effective than helium in reducing the field emission. An interesting observation is the growth of carbon structures after exposure of an electrode to the electric field. Finally, IRFM have performed experiments on a single stage test bushing that features a 36 cm high porcelain insulator and two cylindrical electrode surfaces in vacuum or low-pressure gas. Using 0.1 Pa N2 gas, the voltage holding exceeded 185 kV over a 40 mm "vacuum" gap without dark current. Above this voltage, exterior breakdowns occurred over the insulator, which was in air. The project will finish with the fabrication of a 2-stage compact bushing, capable to withstand 400 kV.

  9. Fuzzy and Multilayer Perceptron for Evaluation of HV Bushings

    CERN Document Server

    Dhlamini, Sizwe M; Majozi, Thokozani

    2007-01-01

    The work proposes the application of fuzzy set theory (FST) to diagnose the condition of high voltage bushings. The diagnosis uses dissolved gas analysis (DGA) data from bushings based on IEC60599 and IEEE C57-104 criteria for oil impregnated paper (OIP) bushings. FST and neural networks are compared in terms of accuracy and computational efficiency. Both FST and NN simulations were able to diagnose the bushings condition with 10% error. By using fuzzy theory, the maintenance department can classify bushings and know the extent of degradation in the component.

  10. Enhanced Dynamic Voltage Stability Support by VSC-HVDC for Offshore Wind Applications using Trajectory Sensitivity Analysis

    DEFF Research Database (Denmark)

    Liu, Hongzhi; Chen, Zhe; Liu, Leo

    2013-01-01

    . In this paper, VSC-HVDC transmission system is used to integrate a large-scale wind power plant into the onshore power grid. For different voltage support strategies of VSC-HVDC, a trajectory sensitivity analysisbased approach is proposed to find the minimum onshore VSC capacity with which the VSC-HVDC can...

  11. Discrete-Time Nonlinear Control of VSC-HVDC System

    Directory of Open Access Journals (Sweden)

    TianTian Qian

    2015-01-01

    Full Text Available Because VSC-HVDC is a kind of strong nonlinear, coupling, and multi-input multioutput (MIMO system, its control problem is always attracting much attention from scholars. And a lot of papers have done research on its control strategy in the continuous-time domain. But the control system is implemented through the computer discrete sampling in practical engineering. It is necessary to study the mathematical model and control algorithm in the discrete-time domain. The discrete mathematical model based on output feedback linearization and discrete sliding mode control algorithm is proposed in this paper. And to ensure the effectiveness of the control system in the quasi sliding mode state, the fast output sampling method is used in the output feedback. The results from simulation experiment in MATLAB/SIMULINK prove that the proposed discrete control algorithm can make the VSC-HVDC system have good static, dynamic, and robust characteristics in discrete-time domain.

  12. Effects of HVDC on power systems small signal angle stability

    Energy Technology Data Exchange (ETDEWEB)

    Custodio, D.T.; Paccini, R.O.; Kopcak, I.; Costa, V.F. da [State University of Campinas (UNICAMP), SP (Brazil). School of Electrical and Computer Engineering. Power Systems Dept.], Emails: totti@dsee.fee.unicamp.br, rodrigo@dsee.fee.unicamp.br, kopcak@dsee.fee.unicamp.br, vivaldo@dsee.fee.unicamp.br

    2009-07-01

    In this paper, a didactic method for parameters tuning of the Power Oscillation Damper (POD) coupled to the HVDC constant current controller is proposed utilizing the MATLAB package with a control system toolbox. First, modal analysis is done from the system state matrix to determine the critical mode and oscillation natural frequency. Input and output linearized matrixes are built to single-input and single-output (SISO) control systems. The phase to be compensated between the active power flow in the parallel AC inter-tie and the current reference signal of the HVDC constant current controller is obtained from the Nyquist theorem. Following, the POD time constants are obtained. Finally, the static gain of the POD is tuned based on the root locus method of the classical control theory. Simulations results prove that the DC power modulation is efficient to damp the AC power oscillations. This method is straightforward because only involves matrix operation. (author)

  13. Subsynchronous torsional interactions with static VAR compensators; Influence of HVDC

    Energy Technology Data Exchange (ETDEWEB)

    Rostamkolai, N.; Piwko, R.J.; Larsen, E.V. (General Electric Co., Schenectady, NY (USA)); Fisher, D.A. (New England Power Service Co., Westborough, MA (USA)); Mobarak, M.A. (New Brunswick Electric Power Commission, Fredericton, NB (Canada)); Poitras, A.E. (Maine Electric Power Co., Augusta, ME (US))

    1991-02-01

    Planning for installation of a static var compensator (SVC) in Chester, Maine, was initiated in 1987. The pre-specification subsynchronous torsional interaction (SSTI) studies showed the SVC might have a negative influence on stability of torsional modes of vibration of the nearby turbine-generators. In a previous paper, the parameters influencing the level of SSTI were identified with the use of a simple system. This paper extends the work to power systems containing an HVDC transmission system. The combined effect of SVC and HVDC on turbine-generator SSTI is investigated with the use of a hypothetical system. Simulation plots for the large machines of New Brunswick and Maine are included to quantify the level of interaction with the Chester SVC. Filtering as a mitigation measure is proposed to eliminate the small level of SSTI attributed to the Chester SVC.

  14. Efficiency of VSC-HVDC System With Various Fuzzy Models

    Directory of Open Access Journals (Sweden)

    Mrs. Sonali R dasgupta,

    2011-05-01

    Full Text Available This paper suggests a Shrinking Span Membership function to be utilized in very fact changing system just like VSC- HVDC system. In this particular work Mamdani controller as well as the Takagi-Sugeno controller are compared with exact same input function(Shrinking Span Membership in simulation as well as on prototype hardware. Simulation result justify the. Takagi-Sugeno Controller gives better dynamic response then the Mamdani controller

  15. Total Magnetic Field Signatures over Submarine HVDC Power Cables

    Science.gov (United States)

    Johnson, R. M.; Tchernychev, M.; Johnston, J. M.; Tryggestad, J.

    2013-12-01

    Mikhail Tchernychev, Geometrics, Inc. Ross Johnson, Geometrics, Inc. Jeff Johnston, Geometrics, Inc. High Voltage Direct Current (HVDC) technology is widely used to transmit electrical power over considerable distances using submarine cables. The most commonly known examples are the HVDC cable between Italy and Greece (160 km), Victoria-Tasmania (300 km), New Jersey - Long Island (82 km) and the Transbay cable (Pittsburg, California - San-Francisco). These cables are inspected periodically and their location and burial depth verified. This inspection applies to live and idle cables; in particular a survey company could be required to locate pieces of a dead cable for subsequent removal from the sea floor. Most HVDC cables produce a constant magnetic field; therefore one of the possible survey tools would be Marine Total Field Magnetometer. We present mathematical expressions of the expected magnetic fields and compare them with fields observed during actual surveys. We also compare these anomalies fields with magnetic fields produced by other long objects, such as submarine pipelines The data processing techniques are discussed. There include the use of Analytic Signal and direct modeling of Total Magnetic Field. The Analytic Signal analysis can be adapted using ground truth where available, but the total field allows better discrimination of the cable parameters, in particular to distinguish between live and idle cable. Use of a Transverse Gradiometer (TVG) allows for easy discrimination between cable and pipe line objects. Considerable magnetic gradient is present in the case of a pipeline whereas there is less gradient for the DC power cable. Thus the TVG is used to validate assumptions made during the data interpretation process. Data obtained during the TVG surveys suggest that the magnetic field of a live HVDC cable is described by an expression for two infinite long wires carrying current in opposite directions.

  16. A New Approach to HVDC Grid Voltage Control Based on Generalized State Feedback

    DEFF Research Database (Denmark)

    Beerten, Jef; Eriksson, Robert; Van Hertem, Dirk

    2014-01-01

    In this paper, a new approach to DC voltage control in a High Voltage Direct Current (HVDC) grid is introduced. In an HVDC grid, the power sharing after a converter outage can be influenced by the droop control values. However, when relying on a local feedback signal, the DC voltage drops...

  17. Transient analysis of an HTS DC power cable with an HVDC system

    Energy Technology Data Exchange (ETDEWEB)

    Dinh, Minh-Chau, E-mail: thanchau7787@gmail.com [Department of Electrical Engineering, Changwon National University, 9 Sarim-Dong, Changwon 641-773 (Korea, Republic of); Ju, Chang-Hyeon; Kim, Jin-Geun; Park, Minwon [Department of Electrical Engineering, Changwon National University, 9 Sarim-Dong, Changwon 641-773 (Korea, Republic of); Yu, In-Keun, E-mail: yuik@cwnu.ac.kr [Department of Electrical Engineering, Changwon National University, 9 Sarim-Dong, Changwon 641-773 (Korea, Republic of); Yang, Byeongmo [Korea Electric Power Research Institute, 105 Munji-Ro, Yuseong-Gu, Daejon 305-760 (Korea, Republic of)

    2013-11-15

    Highlights: •A model of an HTS DC power cable was developed using real time digital simulator. •The simulations of the HTS DC power cable in connection with an HVDC system were performed. •The transient analysis results of the HTS DC power cable were presented. -- Abstract: The operational characteristics of a superconducting DC power cable connected to a highvoltage direct current (HVDC) system are mainly concerned with the HVDC control and protection system. To confirm how the cable operates with the HVDC system, verifications using simulation tools are needed. This paper presents a transient analysis of a high temperature superconducting (HTS) DC power cable in connection with an HVDC system. The study was conducted via the simulation of the HVDC system and a developed model of the HTS DC power cable using a real time digital simulator (RTDS). The simulation was performed with some cases of short circuits that may have caused system damage. The simulation results show that during the faults, the quench did not happen with the HTS DC power cable because the HVDC controller reduced some degree of the fault current. These results could provide useful data for the protection design of a practical HVDC and HTS DC power cable system.

  18. Modeling of HVDC in Dynamic State Estimation Using Unscented Kalman Filter Method

    DEFF Research Database (Denmark)

    Khazraj, Hesam; Silva, Filipe Miguel Faria da; Bak, Claus Leth

    2016-01-01

    HVDC transmission is an integral part of various power system networks. This article presents an Unscented Kalman Filter dynamic state estimator algorithm that considers the presence of HVDC links. The AC - DC power flow analysis, which is implemented as power flow solver for Dynamic State...

  19. Outline of research activity in the HVDC systems

    Energy Technology Data Exchange (ETDEWEB)

    Pigini, A.; Polo Dimel, M.; Testi, G.

    1987-05-01

    The use of HVDC lines in electric power transmission is increasing all over the world. This exceptional increase is the result of the rapid technological development in AC/DC converter stations (power electronics) and of the advantage of HVDC over AC transmission on long distances, submarine connection by means of cables, interconnection of different electric systems, easy control of flowing power, etc. Consequently, also the research and testing activities in this field are under worldwide development. However, research activities imply huge investments and the involment of a lot of personnel. Cooperation agreements such as the one between CESI and CPRI could permit the combination of efforts and the optimization of the results. In this framework, and RandD cooperation programme is on going between the CPRI and CESI (Italy) research facilities. In this paper the facilities available at CESI for carrying out research and tests in the HVDC field are presented and outlines of some studies and tests, already performed, are given. Furthermore, a review of the joint research work which is being carried out by CESI and CPRI is reported.

  20. Waterloo or Milestone of the Bush Administration

    Institute of Scientific and Technical Information of China (English)

    YangHongxi; ChenKaiming; WangWei

    2005-01-01

    In the coming four years, the Middle East will continue to be the strategic focus of the United States. It can be seen in an analysis of the recent years's ituation that the Bush administration rather chose a war in the Middle East to achieve its strategic goals than used non-military measures to do the same thing. In the future the Bush administration might find it difficult to draw back from its policy on the Middle East, which will mean more losses than gains. This will probably continue to cause damage to both the soft and hard power of the U.S., and result in a downward trend of the U.S. power for a certain period of time.

  1. Elecciones en Estados Unidos: Bush contra Kerry

    Directory of Open Access Journals (Sweden)

    Miguel Ángel Valverde Loya

    2004-12-01

    Full Text Available In November 2004, presidential elections took place in the United States. President George W. Bush, a Republican, confronted Democratic candidate John F. Kerry. A very close race was expected, focusing on the economic situation of the country and national security, but it was the latter the one which prevailed during the campaign, even as significant participation was motivated by the issue of “moral values”. It was thought that due to the closeness of the contest, any of the sides could appeal to judicial tribunals, just like four years before. At the end, President Bush achieved a clear victory; both in the popular vote and the electoral college, and his party increased its majorities in both chambers of Congress.

  2. Zinc Oxide Surge Arresters and HVDC 125kV-upgrade 500kV Converter Stations

    Science.gov (United States)

    Shirakawa, Shingo; Kobayashi, Takayuki; Matsushita, Yoshinao; Sakai, Takehisa; Suzuki, Hironori; Ozaki, Yuzo

    Gapless Metal (Zinc) Oxide Surge Arresters for a.c. systems contribute to the insulation co-ordination based on the suppression of lightning surges and switching surges. These gapless metal oxide surge arresters using ZnO elements are effective to HVDC systems. This paper describes basic characteristics of ZnO (zinc oxide) elements for d.c. systems and applications of gapless surge arresters to HVDC 125kV frequency converters, HVDC 250kV, upgrade HVDC 500kV converter stations, and HVDC 500kV cables of Japan through the experience of developments and applications of gapless metal oxide surge arresters.

  3. Coordinated system services from offshore wind power plants connected through HVDC networks

    DEFF Research Database (Denmark)

    Zeni, Lorenzo; Glasdam, Jakob; Hesselbæk, Bo;

    2014-01-01

    This paper presents an overview of power system services in networks involving multiple onshore power systems, a voltage sourced converter (VSC) based high voltage direct current (HVDC) offshore network and an offshore wind power plant (OWPP). A comprehensive list of services regarding onshore...... to their implementation. For example, new findings on onshore AC voltage control are reported, that help the characterisation of potential AC voltage control that a VSC-HVDC station may offer to an onshore AC grid. The HVDC system behind the VSC-HVDC station may connect, through other converters, to another AC power...... system, or an OWPP, or both. Moreover, the implementation of power oscillation damping (POD) and HVDC voltage control into an OWPP controller is proposed, discussing the main challenges related to their efficient design. Dynamic control challenges are assessed, in particular in relation to the inherent...

  4. Contribution of VSC-HVDC to Frequency Regulation of Power Systems With Offshore Wind Generation

    DEFF Research Database (Denmark)

    Liu, Hongzhi; Chen, Zhe

    2015-01-01

    to the onshore system grid through voltage-source converter-based–high voltage direct current (VSC-HVdc) transmission systems. Due to the decoupling of VSC-HVdc and signal transmission delay, offshore wind farms may not be able to respond to the onshore grid frequency excursion in time and, consequently......, the stability and security of the power system will be put at risk, especially for those with high wind penetration. This paper proposes a coordinated control scheme to allow VSC-HVdc link to contribute to the system frequency regulation by adjusting its dc-link voltage. By means of this approach, the dc...... capacitors of VSC-HVdc are controlled to absorb or release energy so as to provide frequency support. To further enhance the system frequency response, the frequency support from VSC-HVdc is also finely coordinated with that from offshore wind farm according to the latency of offshore wind farm responding...

  5. Negative sequence current control in wind power plants with VSC-HVDC connection

    DEFF Research Database (Denmark)

    Chaudhary, Sanjay; Teodorescu, Remus; Rodriguez, Pedro;

    2012-01-01

    Large offshore wind power plants may have multi-MW wind turbine generators (WTG) equipped with full-scale converters (FSC) and voltage source converter (VSC) based high voltaage direct-current (HVDC) transmission for grid connection. The power electronic converters in theWTG-FSC and the VSC-HVDC...... allow fast current control in the offshore grid. This paper presents a method of controlling the negative sequence current injection into the offshore grid from the VSC-HVDC as well as WTG-FSCs. This would minimize the power oscillations and hence reduce the dc voltage overshoots in the VSC-HVDC system...... sequence current control mitigates the power oscillations and therefore limits the dc voltage excursions in the VSC-HVDC system during the asymmetric faults....

  6. Control of a hybrid HVDC link to increase inter-regional power transfer

    DEFF Research Database (Denmark)

    Kotb, Omar; Ghandhari, Mehrdad; Eriksson, Robert

    2016-01-01

    This paper examines the application of a hybrid HVDC link in a two area power system with the purpose of increasing the inter-regional power transfer. A hybrid HVDC system combines both LCCs and VSCs, and hence it is capable of combining the benefits of both converter technologies, such as reduced...... cost and power losses due to the LCCs, and ability to connect to weak AC grids due to the VSCs. The mathematical model of the power system including the HVDC link is presented. The increase in inter-area power transfer is demonstrated and compared to the case when the hybrid HVDC link is not used....... Furthermore, the transient stability of the AC/DC power system was enhanced using auxiliary controllers for Power Oscillation Damping (POD). The results show the ability of the hybrid HVDC link to increase the unidirectional inter-area power transfer, while enhancing the transient stability of the power...

  7. A Two-Dimensional Cloud Model for Condition Assessment of HVDC Converter Transformers

    Directory of Open Access Journals (Sweden)

    Linjie Zhao

    2012-01-01

    Full Text Available Converter transformers are the key and the most important components in high voltage direct current (HVDC power transmission systems. Statistics show that the failure rate of HVDC converter transformers is approximately twice of that of transformers in AC power systems. This paper presents an approach integrated with a two-dimensional cloud model and an entropy-based weight model to evaluate the condition of HVDC converter transformers. The integrated approach can describe the complexity of HVDC converter transformers and achieve an effective assessment of their condition. Data from electrical testing, DGA, oil testing, and visual inspection were chosen to form the double-level assessment index system. Analysis results show that the integrated approach is capable of providing a relevant and effective assessment which in turn, provides valuable information for the maintenance of HVDC converter transformers.

  8. Transient Voltage Stability Analysis and Improvement of A Network with different HVDC Systems

    DEFF Research Database (Denmark)

    Liu, Yan; Chen, Zhe

    2011-01-01

    the theoretical analysis and the improved control method, real time simulation model of a hybrid multi-infeed HVDC system based on western Danish power system is established in RTDS™. Simulation results show that the enhanced transient voltage stability can be achieved.......This paper presents transient voltage stability analysis of an AC system with multi-infeed HVDC links including a traditional LCC HVDC link and a VSC HVDC link. It is found that the voltage supporting capability of the VSC-HVDC link is significantly influenced by the tie-line distance between...... the two links and the size of loads. In order to improve the transient voltage stability, a voltage adjusting method is proposed in this paper. A voltage increment component has been introduced into the outer voltage control loop under emergency situation caused by severe grid faults. In order to verify...

  9. OPF-Based Optimal Location of Two Systems Two Terminal HVDC to Power System Optimal Operation

    Directory of Open Access Journals (Sweden)

    Mehdi Abolfazli

    2013-04-01

    Full Text Available In this paper a suitable mathematical model of the two terminal HVDC system is provided for optimal power flow (OPF and optimal location based on OPF such power injection model. The ability of voltage source converter (VSC-based HVDC to independently control active and reactive power is well represented by the model. The model is used to develop an OPF-based optimal location algorithm of two systems two terminal HVDC to minimize the total fuel cost and active power losses as objective function. The optimization framework is modeled as non-linear programming (NLP and solved by Matlab and GAMS softwares. The proposed algorithm is implemented on the IEEE 14- and 30-bus test systems. The simulation results show ability of two systems two terminal HVDC in improving the power system operation. Furthermore, two systems two terminal HVDC is compared by PST and OUPFC in the power system operation from economical and technical aspects.

  10. Soil microbial communities following bush removal in a Namibian savanna

    Science.gov (United States)

    Buyer, Jeffrey S.; Schmidt-Küntzel, Anne; Nghikembua, Matti; Maul, Jude E.; Marker, Laurie

    2016-03-01

    Savanna ecosystems are subject to desertification and bush encroachment, which reduce the carrying capacity for wildlife and livestock. Bush thinning is a management approach that can, at least temporarily, restore grasslands and raise the grazing value of the land. In this study we examined the soil microbial communities under bush and grass in Namibia. We analyzed the soil through a chronosequence where bush was thinned at 9, 5, or 3 years before sampling. Soil microbial biomass, the biomass of specific taxonomic groups, and overall microbial community structure was determined by phospholipid fatty acid analysis, while the community structure of Bacteria, Archaea, and fungi was determined by multiplex terminal restriction fragment length polymorphism analysis. Soil under bush had higher pH, C, N, and microbial biomass than under grass, and the microbial community structure was also altered under bush compared to grass. A major disturbance to the ecosystem, bush thinning, resulted in an altered microbial community structure compared to control plots, but the magnitude of this perturbation gradually declined with time. Community structure was primarily driven by pH, C, and N, while vegetation type, bush thinning, and time since bush thinning were of secondary importance.

  11. Remarks by president Bush and president Ilves, June 24, 2007 / George W. Bush, Toomas Hendrik Ilves

    Index Scriptorium Estoniae

    Bush, George W., 1946-

    2007-01-01

    Ameerika Ühendriikide president George W. Bush ja Eesti president Toomas Hendrik Ilves annavad lühiülevaateValge Maja ovaalkabinetis peetud kõnelusest, mille põhiteemadeks olid olukord Afganistanis ja Iraagis, viisavabadus ning küberrünnakud. Vabariigi President töövisiidil Ameerika Ühendriikides 25.-26.06.2007

  12. Remarks by president Bush and president Ilves, June 24, 2007 / George W. Bush, Toomas Hendrik Ilves

    Index Scriptorium Estoniae

    Bush, George W., 1946-

    2007-01-01

    Ameerika Ühendriikide president George W. Bush ja Eesti president Toomas Hendrik Ilves annavad lühiülevaateValge Maja ovaalkabinetis peetud kõnelusest, mille põhiteemadeks olid olukord Afganistanis ja Iraagis, viisavabadus ning küberrünnakud. Vabariigi President töövisiidil Ameerika Ühendriikides 25.-26.06.2007

  13. Trend in Bush's China Strategy Adjustment

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    @@ Since the beginning of the year, a debate has been set off on China's rise and China Threat theory is prevailing again in America. Under this background, U.S. Deputy Secretary of State Zoellick delivered a speech on September 21 entitled "Whither China: From Membership to Responsibility?" which systematically elaborated U.S. strategy on China. ① Before and after this speech, many other U.S. politicians and scholars have similar views. This article aims to analyze these relevant expositions in order to explain Bush's China strategy adjustments.

  14. Evaluation of HVDC interconnection models for considering its impact in real-time voltage stability assessment

    DEFF Research Database (Denmark)

    Perez, Angel; Jóhannsson, Hjörtur; Lund, P.;

    2015-01-01

    An approach to evaluate the HVDC interconnectionsmodels to be used in real-time voltage stability assessment is proposed.The existing models for the HVDC interconnections, thatare based on voltage source converter, were studied selecting theones that are suitable for its application in Thevenin...... equivalent ´methods for voltage stability assessment. The proposed methodis to evaluate the validity of the models by using synthetizedPMU measurements from simulations and from PMUs connectedto the danish system. Wide-area measurements are used toestimate the HVDC model parameters which are needed...

  15. An Initial Topology of Multi-terminal HVDC Transmission System in Europe

    DEFF Research Database (Denmark)

    Irnawan, Roni; Silva, Filipe Miguel Faria da; Bak, Claus Leth;

    2016-01-01

    In this paper, technical challenges for realizing offshore multi-terminal HVDC (MTDC) transmission system in Europe is evaluated. An offshore MTDC topology is projected by interconnecting point-to-point HVDC links with the same voltage level and technology found in south-eastern part of North Sea....... Availability analysis is done to evaluate the feasibility of the proposed offshore MTDC topology. As compared to point-to-point (PtP) HVDC link, MTDC operation gives a more secure and reliable system. This paper shows that the proposed MTDC topology can operate 98.36% of the time....

  16. Cluster Control of Offshore Wind Power Plants Connected to a Common HVDC Station

    DEFF Research Database (Denmark)

    Göksu, Ömer; Sakamuri, Jayachandra N.; Rapp, C. Andrea;

    2016-01-01

    In this paper a coordinated control for cluster of offshore WPPs connected to the same HVDC connection is being implemented and analyzed. The study is targeting two cases as; coordination of reactive power flow between HVDC converter and the WPP cluster while providing offshore AC grid voltage...... control, and coordinated closed loop control between the HVDC and the WPPs while the cluster is providing Power Oscillation Damping ( POD) via active power modulation. It is shown that the coordinated cluster control helps to improve the steady-state and dynamic response of the offshore AC grid in case...

  17. Design, control and application of modular multilevel converters for HVDC transmission systems

    CERN Document Server

    Sharifabadi, Kamran; Nee, Hans-Peter; Norrga, Staffan; Teodorescu, Remus

    2016-01-01

    Design, Control and Application of Modular Multilevel Converters for HVDC Transmission Systems is a comprehensive guide to semiconductor technologies applicable for MMC design, component sizing control, modulation, and application of the MMC technology for HVDC transmission. Separated into three distinct parts, the first offers an overview of MMC technology, including information on converter component sizing, Control and Communication, Protection and Fault Management, and Generic Modelling and Simulation. The second covers the applications of MMC in offshore WPP, including planning, technical and economic requirements and optimization options, fault management, dynamic and transient stability. Finally, the third chapter explores the applications of MMC in HVDC transmission and Multi Terminal configurations, including Supergrids.

  18. Grid Code Compliance – Wind farm HVDC connection

    OpenAIRE

    Västermark, Martin

    2013-01-01

    A rapid development of offshore wind power is planned in GB as a part to fulfil the EU2020 targets. 25 GW wind power capacity has been awarded to developers in nine different offshore zones outside the coast of UK. VSC-HVDC transmission is expected to be a both technical and economical favourable solution for transmitting the power into the main grid. This study investigates if such a transmission solution could comply with the regulatory framework in UK. Vattenfall and Scottish Energy Renewa...

  19. HVDC: A key solution in future transmission systems

    Energy Technology Data Exchange (ETDEWEB)

    Heyman, Olof H.; Weimers, Lars; Bohl, Mie-Lotte

    2010-09-15

    With the transition of power grids, based on sustainable generation, HVDC is a key technology with new applications. This includes connection of remote wind parks and strengthening of existing AC grids. In addition, traditional applications, such as bulk hydropower transfer and interconnections between regions, play a major role in our transition to sustainable generation and the associated grids. The technology for regional grids with a limited number of nodes is already in place and commercial projects are commissioned. For extensive grids, development and verification are ongoing in parallel to industry standards being discussed in groups such as ENTSO-E and CIGRE.

  20. Small signal frequency domain model of an HVDC converter

    Energy Technology Data Exchange (ETDEWEB)

    Osauskas, C.M.; Hume, D.J.; Wood, A.R. [UnIversity of Canterbury, Christchurch (New Zealand). Dept. of Electrical and Electronic Engineering

    2001-11-01

    A small-signal analytic frequency domain model of a 6-pulse HVDC converter is presented. The model consists of a set of explicit algebraic equations which relate the transfer of distortion from AC voltage, DC current and firing angle modulation, to AC current and DC voltage. The equations represent the linearisation of the transfers around a base operating point, and are derived from a piecewise linear description of the AC current and DC voltage waveforms. The model provides an understanding of the transfer of distortion by the converter and is in excellent agreement with time domain simulations. (author)

  1. HVDC transmission power conversion applications in power systems

    CERN Document Server

    Kim, Chan-Ki; Jang, Gil-Soo; Lim, Seong-Joo; Lee, Seok-Jin

    2009-01-01

    HVDC is a critical solution to several major problems encountered when trying to maintain systemic links and quality in large-scale renewable energy environments. HDVC can resolve a number of issues, including voltage stability of AC power networks, reducing fault current, and optimal management of electric power, ensuring the technology will play an increasingly important role in the electric power industry. To address the pressing need for an up-to-date and comprehensive treatment of the subject, Kim, Sood, Jang, Lim and Lee have collaborated to produce this key text and reference.  Combin

  2. Coordination Control Strategy for Compound Fault of MMC-HVDC

    OpenAIRE

    Zhang Ming Guang; Zhang Zhao Yu; Qiu Li Jie; Chen Xi

    2016-01-01

    Single-line to ground fault of DC side and sub-module fault are typical faults of MMC-HVDC. When each of the above faults occurs, the system will give a signal for circuit-breaker releasing, this will result in interruption of power delivery, the stability of the system is greatly reduced. When these two faults occur simultaneously, research on control strategy for compound fault will help to improve the reliability of the system. While single-line to ground fault of DC side happens, only the...

  3. Rhetorical and Linguistic Analysis of Bush's Second Inaugural Speech

    Science.gov (United States)

    Sameer, Imad Hayif

    2017-01-01

    This study attempts to analyze Bush's second inaugural speech. It aims at investigating the use of linguistic strategies in it. It resorts to two models which are Aristotle's model while the second is that of Atkinson's (1984) to draw the attention towards linguistic strategies. The analysis shows that Bush's second inaugural speech is successful…

  4. Injection molding of bushes made of tribological PEEK composites

    Directory of Open Access Journals (Sweden)

    2007-12-01

    Full Text Available Polyetheretherketone (PEEK composites have been extensively studied because of the excellent tribological behavior among plastics. However, laboratory specimens and tests are generally discussed, whereas application studies on industrial components are infrequent. In this paper, an injection molded bush made of tribological PEEK was analyzed to correlate wear behavior and molded material structure. Bushes were tested under unlubricated sliding conditions by means of a short wear test. Surface analysis, differential scanning calorimetry (DSC and optical microscopy were used to evaluate the distribution of the different composite fillers (polytetrafluoroethylene, PTFE, graphite particles and carbon microfibers and their effect on the final bush behavior. A significant lack of homogeneity was observed in the molded bush and black bands appeared on the shaft surface after testing due to the sliding. The bush geometry and the injection molding process should be optimized to allow the best tribological behavior of the molded material under working conditions.

  5. Unified active and reactive power modulation of HVDC transmission systems

    Science.gov (United States)

    Grund, C. E.; Pohl, R. V.

    1981-11-01

    The power modulation of a high voltage direct current (HVDC) system for stabilization of an ac/dc network was investigated. It was found that simultaneous modulation of both dc current and voltage was more effective than just current modulation by itself, since the dc voltage modulation could be used to minimize the reactive power changes resulting from a change of the dc current. This helps stabilize the ac busbar voltages at the converters, which reduces undesirable load flow changes to voltage dependent ac loads, thus improving the effectiveness of the dc power modulation. This unified modulation control concept was evaluated by means of digital computer studies as well as a special purpose HVDC simulator. Several combined ac/dc power transmission systems were synthesized for testing of different modulation controller concepts. An optimum controller design incorporating a linear quadratic control algorithm with full state feedback was first studied. This provided a basis for comparison of suboptimal controller designs utilizing reduced state feedback and a Kalman filter state reconstruction technique.

  6. Coordination Control Strategy for Compound Fault of MMC-HVDC

    Directory of Open Access Journals (Sweden)

    Zhang Ming Guang

    2016-01-01

    Full Text Available Single-line to ground fault of DC side and sub-module fault are typical faults of MMC-HVDC. When each of the above faults occurs, the system will give a signal for circuit-breaker releasing, this will result in interruption of power delivery, the stability of the system is greatly reduced. When these two faults occur simultaneously, research on control strategy for compound fault will help to improve the reliability of the system. While single-line to ground fault of DC side happens, only the electric potential auxiliary point of DC side is changed, system’s power transport normally. When sub-module is fault, redundancy fault-tolerated control strategy is presented, which replace the failed sub-modules with equal number of redundant sub-modules, it can restrain the fluctuation of direct current. A double terminals and 21 voltage-level MMC-HVDC system simulation model is set up in PSCAD/EMTDC. From the computation and simulation results, it is concluded that the proposed control strategy is correct for above compound fault, it can achieve rapid recovery after faults, effectively improve fault tolerance of the system, develop the stability and reliability of the system.

  7. Synthesis of a hybrid model of the VSC FACTS devices and HVDC technologies

    Science.gov (United States)

    Borovikov, Yu S.; Gusev, A. S.; Sulaymanov, A. O.; Ufa, R. A.

    2014-10-01

    The motivation of the presented research is based on the need for development of new methods and tools for adequate simulation of FACTS devices and HVDC systems as part of real electric power systems (EPS). The Research object: An alternative hybrid approach for synthesizing VSC-FACTS and -HVDC hybrid model is proposed. The results: the VSC- FACTS and -HVDC hybrid model is designed in accordance with the presented concepts of hybrid simulation. The developed model allows us to carry out adequate simulation in real time of all the processes in HVDC, FACTS devices and EPS as a whole without any decomposition and limitation on their duration, and also use the developed tool for effective solution of a design, operational and research tasks of EPS containing such devices.

  8. Steady-state and transient performance of HVDC link based 3-level ...

    African Journals Online (AJOL)

    Administrateur

    DC (HVDC) transmission systems based on three-level voltage source converters. The study involves ... active AC system at the first end & passive load at the second ..... Simulation of Back-to-Back VSC Transmission System,. Master thesis ...

  9. Power system integration of VSC-HVDC connected offshore wind power plants

    DEFF Research Database (Denmark)

    Zeni, Lorenzo; Kjær, Philip Carne

    . The benefits of not prioritising active power during current-limited operation are demonstrated on a simple system and the possible implications on the control of a WPP potentially connected behind the HVDC converter are discussed. Active power balance control is the second service being analysed......This report presents an overview of challenges and solutions for the integration into the power system of offshore wind power plants (WPPs) connected to onshore grids through a voltage-source converter based high voltage direct current (VSC-HVDC) transmission system. Aspects that are touched upon...... are (i) principles for the control of offshore alternating current (AC) networks behind offshore VSC-HVDC converters, (ii) power system services that could be featured by VSC-HVDC connected WPPs and (iii) clustering of multiple WPPs to co-ordinately provide desired control actions. After a brief...

  10. Power-Hardware-In-the-Loop (PHIL) Test of VSC-based HVDC connection for Offshore Wind Power Plants (WPPs)

    DEFF Research Database (Denmark)

    Sharma, Ranjan; Cha, Seung-Tae; Wu, Qiuwei;

    2011-01-01

    This paper presents a power-hardware-in-the-loop (PHIL) test for an offshore wind power plant (WPP) interconnected to the onshore grid by a VSC-based HVDC connection. The intention of the PHIL test is to verify the control coordination between the plant side converter of the HVDC connection...... the successful control coordination between the WPP and the plant side VSC converter of the HVDC connection of the WPP....

  11. Transporte de energía eléctrica en corriente contínua. Enlaces HVDC-VSC

    OpenAIRE

    Monterrubio Díez, Mario

    2013-01-01

    El proyecto fin de carrera se plantea como un estudio de la tecnología HVDC-VSC, por su carácter novedoso y reciente implantación en los sistemas de transporte de electricidad. Con este trabajo se pretende dar a conocer de modo general la tecnología HVDC y de manera particular la variante HVDC-VSC.

  12. Restoration of Normal Frequency Affected by Small Load Variations Through HVDC link Using Neuro-Fuzzy Approach

    OpenAIRE

    Anil Kumar Sharma,; Dr. G. K. Joshi,; Tarun Kumar De; Shyam Krishan Joshi

    2011-01-01

    HVDC power transmission is coming up with merits to replace the EHV-AC system. The controller inverter operation can successfully regulate the power in HVDC link leading to fulfillment ofpower demand in A.C. networks caused by sudden rise in loading. Since overloading and unloading both lead to the departure of operating frequency below or above normal, its control for normalization isexercised through control of power flow in HVDC Link. Also the same is achieved by adjusting firing delay ang...

  13. HVDC Connected Offshore Wind Power Plants: Review and Outlook of Current Research

    DEFF Research Database (Denmark)

    Glasdam, Jakob Bærholm; Zeni, Lorenzo; Gryning, Mikkel

    2013-01-01

    these challenges through three coordinated PhD projects in close collaboration with leading academia within the field. The overall goal of these projects is to acquire indepth knowledge of relevant operating phenomena in the offshore OWPP grid, rich with power electronics devices (PEDs) such as the HVDC...... of the projects will be developed and validated models of e.g. the HVDC system, methodologies for assessment of control system stability and fault identification in implemented control system....

  14. HVDC Connected Offshore Wind Power Plants: Review and Outlook of Current Research

    DEFF Research Database (Denmark)

    Glasdam, Jakob; Zeni, Lorenzo; Gryning, Mikkel

    2013-01-01

    these challenges through three coordinated PhD projects in close collaboration with leading academia within the field. The overall goal of these projects is to acquire in-depth knowledge of relevant operating phenomena in the offshore OWPP grid, rich with power electronics devices (PEDs) such as the HVDC...... of the projects will be developed and validated models of e.g. the HVDC system, methodologies for assessment of control system stability and fault identification in implemented control system....

  15. Innovation on Energy Power Technology (8)First HVDC Transmission System in Japan

    Science.gov (United States)

    Sampei, Masatoshi

    This paper is an episode concerning the Hokkaido-Honshu HVDC Link that is the first High Voltage DC Current transmission system in Japan. The effort to the commissioning of the first stage of this system is explained. Moreover, it explains the research and development executed to achieve 600MW of this system that is the final stage. In addition, the adoption episode of the frequency control method introduced for Hokkaido-Honshu HVDC Link is explained.

  16. Alternatives for Primary Frequency Control Contribution from Wind Power Plants Connected to VSC-HVDC Intertie

    DEFF Research Database (Denmark)

    Laukhamar, Andreas Grøsvik; Zeni, Lorenzo; Sørensen, Poul Ejnar

    how a large offshore wind power plant (OWPP) with high voltage direct current (HVDC) intertie connection to two asynchronous onshore AC power systems can be part of the solution in providing short-term mutual active power balancing. The primary frequency control is investigated for four different...... in a sharing of the primary reserves and rolling inertia between the two onshore AC power systems connected to the HVDC intertie, whilst also exploiting the OWPP in the primary frequency control scheme....

  17. HVDC System Stability – Analysis, Monitoring and Control in Wide Area Power Systems

    OpenAIRE

    Kuehn, Walter; Vanfretti, Luigi; Fischer, W.

    2014-01-01

    To a great extent future electric power systems will use HVDC technologies, based on either current sourced or voltage sourced converters (CSC, resp. VSC). Both technologies have their merits and range of applications being connected to technical capabilities, costs and operational properties and performance. Voltage stability is an important issue in classical CSC-based HVDC systems, while voltage stability and angle stability (both transmission angle and rotor angle) are of concern in VSC-H...

  18. Power Flow Algorithms for Multi-Terminal VSC-HVDC With Droop Control

    OpenAIRE

    Wang, Wenyuan; Barnes, Mike

    2014-01-01

    This paper addresses the problem posed by complex, nonlinear controllers for power system load flows employing multi-terminal voltage source converter (VSC) HVDC systems. More realistic dc grid control strategies can thus be carefully considered in power flow analysis of ac/dc grids. Power flow methods for multi-terminal VSC-HVDC (MTDC) systems are analyzed for different types of dc voltage control techniques and the weaknesses of present methods are addressed. As distributed voltage control ...

  19. Offshore Wind Park Connection to an HVDC Platform, without using an AC Collector Platform

    OpenAIRE

    Ahmad, Haseeb

    2012-01-01

    This thesis investigates the comparison between two different alternating current topologies of an offshore wind farms connection to an offshore high voltage direct current (HVDC) converter platform. The offshore high voltage direct current converter platform converts alternating current into direct current. Two different topologies will be investigated. In the first topology, the offshore wind farms are connected to an HVDC converter platform through offshore AC collector platform. An offsho...

  20. 交流系统故障时 VSC-HVDC 的保护策略研究

    Institute of Scientific and Technical Information of China (English)

    王帅

    2015-01-01

    本文分析了交流系统电压平衡时 VSC-HVDC 系统的控制策略,阐述了柔性直流输电系统的控制,SC-HVDC 系统的控制策略,内环电流控制器设计,VSC-HVDC 系统仿真与分析,指出交流系统故障时VSC-HVDC 系统的控制策略。

  1. Simulative Study into the Development of a Hybrid HVDC System Through a Comparative Research with HVAC: a Futuristic Approach

    Directory of Open Access Journals (Sweden)

    R. S. Narayan

    2017-06-01

    Full Text Available High Voltage Direct Current Transmission (HVDC is considered a better solution for bulk long distance transmissions. The increased use of HVDC is a result of its advantages over the HVAC systems and especially of its fault stability nature. A better solution is proposed by using a Voltage Source Controlled–HVDC as one of the infeed for the Multi-Infeed HVDC (MIDC or MI-HVDC systems. The main advantage with the VSC converter is its flexible power control which enhances the stability of the MIDC systems. In this paper, the behavior of an HVDC system is compared with that of an HVAC during faults. A Hybrid HVDC system that includes a LCC as a rectifier unit and a VSC converter as the inverter is being proposed. It is considered suitable for MIDC systems and particularly for supplying a weak AC system. The performance of the system during steady state and transient conditions for all the proposed topologies including HVDC, HVAC and Hybrid HVDC are studied in MATLAB/SIMULINK. All of the proposed control strategies are evaluated via a series of simulation case studies.

  2. Coordinated Control Strategies of VSC-HVDC-Based Wind Power Systems for Low Voltage Ride Through

    Directory of Open Access Journals (Sweden)

    Xinyin Zhang

    2015-07-01

    Full Text Available The Voltage Source Converter-HVDC (VSC-HVDC system applied to wind power generation can solve large scale wind farm grid-connection and long distance transmission problems. However, the low voltage ride through (LVRT of the VSC-HVDC connected wind farm is a key technology issue that must be solved, and it is currently lacking an economic and effective solution. In this paper, a LVRT coordinated control strategy is proposed for the VSC-HVDC-based wind power system. In this strategy, the operation and control of VSC-HVDC and wind farm during the grid fault period is improved. The VSC-HVDC system not only provides reactive power support to the grid, but also effectively maintains the power balance and DC voltage stability by reducing wind-farm power output, without increasing the equipment investment. Correspondingly, to eliminate the influence on permanent magnet synchronous generator (PMSG-based wind turbine (WT systems, a hierarchical control strategy is designed. The speed and validity of the proposed LVRT coordinated control strategy and hierarchical control strategy were verified by MATLAB/Simulink simulations.

  3. Mitigation of commutation failures in LCC-HVDC systems based on superconducting fault current limiters

    Science.gov (United States)

    Lee, Jong-Geon; Khan, Umer Amir; Lee, Ho-Yun; Lim, Sung-Woo; Lee, Bang-Wook

    2016-11-01

    Commutation failure in line commutated converter based HVDC systems cause severe damages on the entire power grid system. For LCC-HVDC, thyristor valves are turned on by a firing signal but turn off control is governed by the external applied AC voltage from surrounding network. When the fault occurs in AC system, turn-off control of thyristor valves is unavailable due to the voltage collapse of point of common coupling (PCC), which causes the commutation failure in LCC-HVDC link. Due to the commutation failure, the power transfer interruption, dc voltage drop and severe voltage fluctuation in the AC system could be occurred. In a severe situation, it might cause the protection system to block the valves. In this paper, as a solution to prevent the voltage collapse on PCC and to limit the fault current, the application study of resistive superconducting fault current limiter (SFCL) on LCC-HVDC grid system was performed with mathematical and simulation analyses. The simulation model was designed by Matlab/Simulink considering Haenam-Jeju HVDC power grid in Korea which includes conventional AC system and onshore wind farm and resistive SFCL model. From the result, it was observed that the application of SFCL on LCC-HVDC system is an effective solution to mitigate the commutation failure. And then the process to determine optimum quench resistance of SFCL which enables the recovery of commutation failure was deeply investigated.

  4. Mitigation of commutation failures in LCC–HVDC systems based on superconducting fault current limiters

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jong-Geon; Khan, Umer Amir; Lee, Ho-Yun; Lim, Sung-Woo; Lee, Bang-Wook, E-mail: bangwook@hanyang.ac.kr

    2016-11-15

    Commutation failure in line commutated converter based HVDC systems cause severe damages on the entire power grid system. For LCC–HVDC, thyristor valves are turned on by a firing signal but turn off control is governed by the external applied AC voltage from surrounding network. When the fault occurs in AC system, turn-off control of thyristor valves is unavailable due to the voltage collapse of point of common coupling (PCC), which causes the commutation failure in LCC–HVDC link. Due to the commutation failure, the power transfer interruption, dc voltage drop and severe voltage fluctuation in the AC system could be occurred. In a severe situation, it might cause the protection system to block the valves. In this paper, as a solution to prevent the voltage collapse on PCC and to limit the fault current, the application study of resistive superconducting fault current limiter (SFCL) on LCC–HVDC grid system was performed with mathematical and simulation analyses. The simulation model was designed by Matlab/Simulink considering Haenam-Jeju HVDC power grid in Korea which includes conventional AC system and onshore wind farm and resistive SFCL model. From the result, it was observed that the application of SFCL on LCC–HVDC system is an effective solution to mitigate the commutation failure. And then the process to determine optimum quench resistance of SFCL which enables the recovery of commutation failure was deeply investigated.

  5. Offshore grid transmission planning using approximated HVDC power flows

    Energy Technology Data Exchange (ETDEWEB)

    Torbaghan, Shahab Shariat; Rawn, Barry G.; Gibescu, Madeleine; Meijden, Mart van der [Delft Univ. of Technology (Netherlands). Dept. of Electrical Sustainable Energy

    2012-07-01

    In this paper we introduce an optimization framework which determines a socially optimum design of a HVDC offshore grid, under the assumption of a centralized network expansion planning scheme. This gives the optimum grid topology and interconnections capacity. In addition, the analytical solution to the optimization problem yields a market structure that expresses the relationship between the different regions' electricity prices and congestion charges associated with the interconnections. The optimization model sets the transmission capacities in a way that congestion shadow prices to be collected by the end of the economic lifetime of the project pay off the initial investment capital. We use this framework to study the impact of exercising different dispatching policies on the optimum design of the grid. The framework is applied to a multi-bus test system that functions under 8 different time periods. (orig.)

  6. Aswan HighDam/Cairo proposed HVDC transmission system

    Directory of Open Access Journals (Sweden)

    Ahmed Y.M.R. Salama

    2014-03-01

    The DC lines can carry more much power with two conductors than the power transmitted using an AC lines with three conductors of the same size. For the given power level, a DC line requires simpler and cheaper towers (From economical point of view, already installed towers for AC system can be used. Also reduced conductor sizes and insulator can be used. The power transmission losses also will be reduced to about two-thirds of the comparable AC system. The absence of skin effect with DC is also beneficial in reducing power losses marginally. Due to its fast controllability, HVDC transmission system has full control over transmitted power, an ability to enhance transient and dynamic stability in associated AC networks and can limit fault currents levels in the DC lines.

  7. Improvement of Wind Energy Production through HVDC Systems

    Directory of Open Access Journals (Sweden)

    Morris Brenna

    2017-01-01

    Full Text Available Variable and non-programmable resources, such as solar and wind, have undergone a stunning growth in recent years and are likely to gain even more importance in the future. Their strong presence in the national electricity mix has created issues in many countries regarding the secure operation of the power system. In order to guarantee the stability of the system, several TSOs have resorted to wind energy curtailment, which represents a waste of clean energy and an economic loss. In order to analyze this issue, a model of the Italian power system was developed, a program able to simulate the electricity dispatching mechanism. The model was, then, used to evaluate possible solutions to reduce wind curtailment. In particular, a proposal for the construction of an HVDC line linking Southern and Northern Italy was studied.

  8. Cost estimation of HVDC transmission system of Bangka's NPP candidates

    Science.gov (United States)

    Liun, Edwaren; Suparman

    2014-09-01

    Regarding nuclear power plant development in Bangka Island, it can be estimated that produced power will be oversupply for the Bangka Island and needs to transmit to Sumatra or Java Island. The distance between the regions or islands causing considerable loss of power in transmission by alternating current, and a wide range of technical and economical issues. The objective of this paper addresses to economics analysis of direct current transmission system to overcome those technical problem. Direct current transmission has a stable characteristic, so that the power delivery from Bangka to Sumatra or Java in a large scale efficiently and reliably can be done. HVDC system costs depend on the power capacity applied to the system and length of the transmission line in addition to other variables that may be different.

  9. Limiting electric fields of HVDC overhead power lines.

    Science.gov (United States)

    Leitgeb, N

    2014-05-01

    As a consequence of the increased use of renewable energy and the now long distances between energy generation and consumption, in Europe, electric power transfer by high-voltage (HV) direct current (DC) overhead power lines gains increasing importance. Thousands of kilometers of them are going to be built within the next years. However, existing guidelines and regulations do not yet contain recommendations to limit static electric fields, which are one of the most important criteria for HVDC overhead power lines in terms of tower design, span width and ground clearance. Based on theoretical and experimental data, in this article, static electric fields associated with adverse health effects are analysed and various criteria are derived for limiting static electric field strengths.

  10. Coordinated control of wind power plants in offshore HVDC grids

    DEFF Research Database (Denmark)

    Sakamuri, Jayachandra N.

    2017-01-01

    During the recent years, there has been a significant penetration of offshore wind power into the power system and this trend is expected to continue in the future. The North Sea in Europe has higher potential for offshore wind power; therefore, the North Seas Countries' Offshore Grid initiative...... power between different countries, and different synchronous areas. It is very likely that they will then be combined with offshore wind power plant (OWPP) connections in the North Sea, transforming it in a multi terminal DC (MTDC) grid and, therefore, in a fully meshed offshore DC grid in near future...... was formed among nine North Sea countries. They agreed on closer energy cooperation to enable development of an efficient and economic offshore grid infrastructure for advantages, interconnectors based on the voltage source converter based high voltage DC (HVDC) transmission system is being used to exchange...

  11. Lifetime Estimation of MMC for Offshore Wind Power HVDC Application

    DEFF Research Database (Denmark)

    Liu, Hui; Ma, Ke; Qin, Zian;

    2016-01-01

    Due to a series of unique merits, Modular Multilevel Converters (MMCs) have been developing dramatically in the last decade. However in some applications like offshore power transmission the MMC modules are subjected to a variety of tough temperature profiles with adverse working condition, all......) application for offshore wind power. The mission profiles as well as the topology of the MMC are first analyzed in order to better understand the loading characteristics of MMC. Then the power loss calculation along with the electro-thermal simulation is conducted to uncover the thermal loading of MMC...... of these could lead to thermomechanical fatigues in the components and joints of the power modules and thereby causing reliability challenge. This study focuses on the lifetime evaluation of MMC based on power cycling and thermal cycling considering the mission profiles in the High Voltage Direct Current (HVDC...

  12. Lifetime Estimation of MMC for Offshore Wind Power HVDC Application

    DEFF Research Database (Denmark)

    Liu, Hui; Ma, Ke; Loh, Poh Chiang

    2014-01-01

    Due to a series of unique merits, Modular Multilevel Converters (MMCs) have been developing dramatically in the last decade. However in some applications like offshore power transmission the MMC modules are subjected to a variety of tough temperature profiles with adverse working condition, all...... of these could lead to thermo-mechanical fatigues in the components and joints of the power modules and thereby causing reliability challenge. This study focuses on the lifetime evaluation of MMC based on power cycling and thermal cycling considering the mission profiles in the High Voltage Direct Current (HVDC......) application for offshore wind power. The mission profiles as well as the topology of the MMC are first analyzed in order to better understand the loading profiles of MMC. Then the power loss calculation along with the electro-thermal simulation is conducted to uncover the thermal loading of MMC. At last...

  13. Bush asub uue Iraagi-poliitikaga vigu parandama / Kaivo Kopli

    Index Scriptorium Estoniae

    Kopli, Kaivo

    2007-01-01

    USA president George W. Bush tutvustas uut Iraagi-strateegiat. Iraaki saadetakse paarkümmend tuhat USA sõdurit, küsitluse andmeil on 61% ameeriklastest lisasõdurite saatmise vastu. Lisa: USA plaanid Iraagis ja Iraagiga

  14. Bush asub uue Iraagi-poliitikaga vigu parandama / Kaivo Kopli

    Index Scriptorium Estoniae

    Kopli, Kaivo

    2007-01-01

    USA president George W. Bush tutvustas uut Iraagi-strateegiat. Iraaki saadetakse paarkümmend tuhat USA sõdurit, küsitluse andmeil on 61% ameeriklastest lisasõdurite saatmise vastu. Lisa: USA plaanid Iraagis ja Iraagiga

  15. Insulation Characteristics of Bushing Shed at Cryogenic Temperature

    Science.gov (United States)

    Kim, W. J.; Kim, Y. J.; Kim, S. H.

    2014-05-01

    In the development of high-Tc superconducting(HTS) devices, the bushing for HTS devices (HTS bushing) is the core technology, the need to because of supply high voltage to the cable or the winding of the transformer. The lower part of the bushing is exposed to the liquid nitrogen (LN2), and it has many sheds. In particular, the insulation body with sheds and electrical insulation at cryogenic temperature have attracted a great deal of interest from the view point of the size, weight and efficiency of bushing. This study has mainly investigated the shed and insulation body by comparing glass fiber reinforced plastics (GFRP) in LN2. We investigated the surface discharge characteristics according to insulating materials, width and height of the shed.

  16. Baltic leaders jockey with Bush to get their message across

    Index Scriptorium Estoniae

    2005-01-01

    USA president George Bush lubas pärast kõnelemist Mart Laari ning Vaira Vike-Freibergaga arutada kohtumisel president Vladimir Putiniga suhteid Venemaa ja Balti riikide vahel. Lisa: Vladimir Putini arvamus Molotovi-Ribbentropi pakti kohta

  17. Allergenic sesquiterpene lactones from cushion bush (Leucophyta brownii Cass.)

    DEFF Research Database (Denmark)

    Paulsen, Evy; Gade Hyldgaard, Mette; Andersen, Klaus E.

    2017-01-01

    BACKGROUND: The Australian cushion bush (Leucophyta brownii) of the Compositae family of plants has become a popular pot and container plant. The plant produces the sesquiterpene lactone allergen calocephalin. OBJECTIVES: To assess the sensitizing potential of sesquiterpene lactones from cushion ...

  18. Bush võitleb tugeva presidendi maine nimel / Neeme Raud

    Index Scriptorium Estoniae

    Raud, Neeme, 1969-

    2007-01-01

    Ilmunud ka: Postimees : na russkom jazõke, 13. juuni 2007, lk. 5. USA president George W. Bush pidi sekkuma immigratsioonireformi debatti. Vt. samas: Malta ja Rootsi nõuavad sisserändajate jagamist

  19. Election Watch: Buchanan Candidacy Dismays Pro-Israel Bush Bashers

    National Research Council Canada - National Science Library

    Barnes, Lucille

    1992-01-01

    ...]...The dual threat has rallied Jewish Republicans to the president's banner. `The presence of these men has accelerated the mobilization of Jewish Republicans behind Bush in the primaries,' said a leading Jewish Republican activist...

  20. Bush jätkab maailma dirigeerimist / Neeme Raud

    Index Scriptorium Estoniae

    Raud, Neeme, 1969-

    2004-01-01

    USA president George W. Bush peab oma tagasivalimise kindlustajaks elluviidud välispoliitikat. Autori hinnangul on Bush varasematest presidentidest jõulisemalt muutmas USA-d kapitalismi lipulaevaks, Bushi USA vastandab end euroopalikule mudelile, kus riik tagab kodanikele turvatunde. Kavandatavatest muudatustest USA sisepoliitikas. Vt. samas: Arko Olesk. Verine aasta Iraagi sõjas; Aivar Reinap. USA majandus mustas augus; Andres Keil. Tsivilisatsiooni häirekell

  1. Contributions on Computer Aided Manufacturing of Drill-Jig Bushings

    Directory of Open Access Journals (Sweden)

    Vasile Cojocaru

    2009-01-01

    Full Text Available The paper presents the steps for computer aided manufacturing (CAMof the bushings technological class parts: design of the part in CADsoftware; generation of the parametrical link with MSExcel files; extract of the useful information for the technological design (mass, volume, surfaces; setting of the CNC lathe and necessary tools; programming of the CNC code for manufacturing. Given the large variety of the bushingsshapes and dimensions, the application focused on the jig bushings used in drilling processes.

  2. The Bush administration climate proposal: rhetoric and reality

    Energy Technology Data Exchange (ETDEWEB)

    Blanchard, O.

    2003-03-01

    This paper examines the Bush administration proposal and subsequent actions in terms of the United Nations Framework Convention on Climate Change (UNFCCC). It has four sections. Section one describes the main features of the Bush Administration climate proposal. Section 2 identifies the main underlying factors that shape this proposal. Section 3 rebuts the Administration critique in deciding to reject the Kyoto protocol. Section 4 explores the prospects of the US climate mitigation actions over the next few years. (A.L.B.)

  3. Performance analysis of a model-sized superconducting DC transmission system based VSC-HVDC transmission technologies using RTDS

    Science.gov (United States)

    Dinh, Minh-Chau; Ju, Chang-Hyeon; Kim, Sung-Kyu; Kim, Jin-Geun; Park, Minwon; Yu, In-Keun

    2012-08-01

    The combination of a high temperature superconducting DC power cable and a voltage source converter based HVDC (VSC-HVDC) creates a new option for transmitting power with multiple collection and distribution points for long distance and bulk power transmissions. It offers some greater advantages compared with HVAC or conventional HVDC transmission systems, and it is well suited for the grid integration of renewable energy sources in existing distribution or transmission systems. For this reason, a superconducting DC transmission system based HVDC transmission technologies is planned to be set up in the Jeju power system, Korea. Before applying this system to a real power system on Jeju Island, system analysis should be performed through a real time test. In this paper, a model-sized superconducting VSC-HVDC system, which consists of a small model-sized VSC-HVDC connected to a 2 m YBCO HTS DC model cable, is implemented. The authors have performed the real-time simulation method that incorporates the model-sized superconducting VSC-HVDC system into the simulated Jeju power system using Real Time Digital Simulator (RTDS). The performance analysis of the superconducting VSC-HVDC systems has been verified by the proposed test platform and the results were discussed in detail.

  4. Modular VSC converter based HVDC power transmission from offshore wind power plant: Compared to the conventional HVAC system

    DEFF Research Database (Denmark)

    Sharma, Ranjan; Rasmussen, Tonny Wederberg; Jensen, Kim Høj;

    2010-01-01

    power transmission options with HVDC systems are under consideration. In this paper, a comparison between a conventional HVAC transmission system and a HVDC system equipped with modular voltage source converters is provided. The comparison is based on the total energy transmission capability...

  5. Steady-state operational range evolution from a two-terminal to a multiterminal HVDC transmission system

    DEFF Research Database (Denmark)

    Irnawan, Roni; Silva, Filipe Miguel Faria da; Bak, Claus Leth;

    2017-01-01

    DC grids are anticipated to grow organically with one possible initial configuration being formed by interconnecting an additional HVDC converter into an existing shore-to-shore (StS) HVDC link. In order to ensure the performance of this MTDC system, the DC voltage at each converter terminal within...

  6. Cooperative control of VSC-HVDC connected offshore wind farm with Low-Voltage Ride-Through capability

    DEFF Research Database (Denmark)

    Liu, Yan; Wang, Xiongfei; Chen, Zhe

    2012-01-01

    The Low-Voltage Ride-Through (LVRT) has become an important grid requirement for offshore wind farms connecting with Voltage Source Converter based High Voltage Direct Current (VSC-HVDC) links. In this paper, a cooperative control strategy with LVRT ability is proposed for a VSC-HVDC connected va...

  7. Modelling and Simulation of SVPWM Based Vector Controlled HVDC Light Systems

    Directory of Open Access Journals (Sweden)

    Ajay Kumar MOODADLA

    2012-11-01

    Full Text Available Recent upgrades in power electronics technology have lead to the improvements of insulated gate bipolar transistor (IGBT based Voltage source converter High voltage direct current (VSC HVDC transmission systems. These are also commercially known as HVDC Light systems, which are popular in renewable, micro grid, and electric power systems. Out of different pulse width modulation (PWM schemes, Space vector PWM (SVPWM control scheme finds growing importance in power system applications because of its better dc bus utilization. In this paper, modelling of the converter is described, and SVPWM scheme is utilized to control the HVDC Light system in order to achieve better DC bus utilization, harmonic reduction, and for reduced power fluctuations. The simulations are carried out in the MATLAB/SIMULINK environment and the results are provided for steady state and dynamic conditions. Finally, the performance of SVPWM based vector controlled HVDC Light transmission system is compared with sinusoidal pulse width modulation (SPWM based HVDC Light system in terms of output voltage and total harmonic distortion (THD.

  8. Transmission of Power to the Island Using HVDC (From Indian continent to Lakshadweep island

    Directory of Open Access Journals (Sweden)

    B. Vijayalakshmi

    2012-09-01

    Full Text Available HVDC transmission is more effective and economically cheaper where bulk power is to be transmitted over long distance. Hence the surplus power from a remote place can be exported to the needy place at cheaper rate. The HVDC system require only one transmission wire and the ground return or seawater can be used as an another line. The Lakshadweep Island is located at faraway place from the northeast part of India where the surplus power is available. The seawater for return path is available. The diesel for D.G set is transported from Indian mainland through ship where lot of economy is lost only for transportation. In this paper the transmission of HVDC from Indian mainland to Lakshadweep is analyzed at economically cheaper rate.

  9. Fault Ride-Through Capability Enhancement of VSC HVDC connected Offshore Wind Power Plants

    DEFF Research Database (Denmark)

    Sharma, Ranjan; Wu, Qiuwei; Cha, Seung-Tae;

    2015-01-01

    This paper presents a feed forward direct current (DC) voltage control based fault ride-through (FRT) scheme for voltage source converter (VSC) high voltage DC (HVDC) connected offshore wind power plants (WPPs) in order to achieve active control of the WPP collector network AC voltage magnitude......, and to improve the FRT capability. During steady state operation, an open loop AC voltage control is implemented at the WPP side VSC of the HVDC system such that any possible control interactions between the WPP side VSC and the wind turbine VSC are minimized. Whereas during any grid faults, a dynamic AC voltage...... reference is applied based on both the DC voltage error and the AC active-current from the WPP collector system which ensures fast and robust FRT of the VSC HVDC connected offshore WPPs. Under unbalanced fault conditions in the host power system, the resulting oscillatory DC voltage is directly used...

  10. Voltage Stability Bifurcation Analysis for AC/DC Systems with VSC-HVDC

    Directory of Open Access Journals (Sweden)

    Yanfang Wei

    2013-01-01

    Full Text Available A voltage stability bifurcation analysis approach for modeling AC/DC systems with VSC-HVDC is presented. The steady power model and control modes of VSC-HVDC are briefly presented firstly. Based on the steady model of VSC-HVDC, a new improved sequential iterative power flow algorithm is proposed. Then, by use of continuation power flow algorithm with the new sequential method, the voltage stability bifurcation of the system is discussed. The trace of the P-V curves and the computation of the saddle node bifurcation point of the system can be obtained. At last, the modified IEEE test systems are adopted to illustrate the effectiveness of the proposed method.

  11. Real power regulation design for multi-terminal VSC-HVDC systems

    Science.gov (United States)

    Li, Guo-Jie; Ruan, Si-Ye; Lie, Tek

    2013-06-01

    A multi-terminal voltage-source-converter (VSC) based high voltage direct current (HVDC) system is concerned for its flexibility and reliability. In this study, a control strategy for multiple VSCs is proposed to auto-share the real power variation without changing control mode, which is based on "dc voltage droop" power regulation functions. With the proposed power regulation design, the multiple VSCs automatically share the real power change and the VSC-HVDC system is stable even under loss of any one converter while there is no overloading for any individual converter. Simulation results show that it is effective to balance real power for power disturbance and thus improves operation reliability for the multi-terminal VSC-HVDC system by the proposed control strategy.

  12. Centrally Coordinated Control of Multiple HVDC Links for Power Oscillation Damping

    Science.gov (United States)

    Eriksson, Robert; Söder, Lennart

    2010-06-01

    This paper presents a method of how to design a centrally coordinated controller for several HVDC links. The controller increases the damping of the power oscillations by modulating the current through the HVDC links coordinately. To design a centrally coordinated controller a reduced order open system model is estimated. The open system model of the power system is developed by using black-box system identifications techniques. The current setpoint change through the HVDC links is the set of input signals and, the speeds of the generators are the set of outputs. Numerical Algorithms for Subspace State-Space System Identification (N4SID) is used to identify a model. This controller design method increases the damping significantly which is shown for a small power system.

  13. Detailed Equivalent VSC-HVDC Modelling for Time Domain Harmonic Stability Studies in Wind Power Plants

    DEFF Research Database (Denmark)

    Glasdam, Jakob Bærholm; Bak, Claus Leth; Kocewiak, Lukasz Hubert;

    2017-01-01

    This paper presents a detailed equivalent modelling approach of the modular multi-level cascaded converter (MMCC) voltage source converter high voltage direct current (VSC-HVDC) in electromagnetic transient programs (EMTPs). The presented MMCC model will be evaluated based on comparison with the ......This paper presents a detailed equivalent modelling approach of the modular multi-level cascaded converter (MMCC) voltage source converter high voltage direct current (VSC-HVDC) in electromagnetic transient programs (EMTPs). The presented MMCC model will be evaluated based on comparison...... generators in service, as this is known to influence the harmonic stability in OWPPs. The paper demonstrates the necessity of the inclusion of a detailed equivalent model of the HVDC converter for harmonic stability studies in the time domain. By implementation of active filtering in the converters...

  14. DC breakdown characteristics of silicone polymer composites for HVDC insulator applications

    Science.gov (United States)

    Han, Byung-Jo; Seo, In-Jin; Seong, Jae-Kyu; Hwang, Young-Ho; Yang, Hai-Won

    2015-11-01

    Critical components for HVDC transmission systems are polymer insulators, which have stricter requirements that are more difficult to achieve compared to those of HVAC insulators. In this study, we investigated the optimal design of HVDC polymer insulators by using a DC electric field analysis and experiments. The physical properties of the polymer specimens were analyzed to develop an optimal HVDC polymer material, and four polymer specimens were prepared for DC breakdown experiments. Single and reverse polarity breakdown tests were conducted to analyze the effect of temperature on the breakdown strength of the polymer. In addition, electric fields were analyzed via simulations, in which a small-scale polymer insulator model was applied to prevent dielectric breakdown due to electric field concentration, with four DC operating conditions taken into consideration. The experimental results show that the electrical breakdown strength and the electric field distribution exhibit significant differences in relation to different DC polarity transition procedures.

  15. Grid-connection of large offshore windfarms utilizing VSC-HVDC: Modeling and grid impact

    DEFF Research Database (Denmark)

    Xue, Yijing; Akhmatov, Vladislav

    2009-01-01

    Utilization of Voltage Source Converter (VSC) – High Voltage Direct Current (HVDC) systems for grid-connection of large offshore windfarms becomes relevant as installed power capacities as well as distances to the connection points of the on-land transmission systems increase. At the same time......, the grid code requirements of the Transmission System Operators (TSO), including ancillary system services and Low-Voltage Fault-Ride-Through (LVFRT) capability of large offshore windfarms, become more demanding. This paper presents a general-level model of and a LVFRT solution for a VSC-HVDC system...... for grid-connection of large offshore windfarms. The VSC-HVDC model is implemented using a general approach of independent control of active and reactive power in normal operation situations. The on-land VSC inverter, which is also called a grid-side inverter, provides voltage support to the transmission...

  16. Application of VSC-HVDC with Shunt Connected SMES for Compensation of Power Fluctuation

    Science.gov (United States)

    Linn, Zarchi; Kakigano, Hiroaki; Miura, Yushi; Ise, Toshifumi

    This paper describes the application of VSC-HVDC (High Voltage DC Transmission using Voltage Source Converter) with shunt connected SMES (Superconducting Magnetic Energy Storage) for compensation of power fluctuation caused by fluctuating power source such as photovoltaics and wind turbines. The objectives of this proposed system is to smooth out fluctuating power in one terminal side of HVDC in order to avoid causing power system instability and frequency deviation by absorbing or providing power according to the system requirement while another terminal side power is fluctuated. The shunt connected SMES charges and discharges the energy to and from the dc side and it compensates required power of fluctuation to obtain constant power flow in one terminal side of VSC-HVDC system. This system configuration has ability for power system stabilization in the case of power fluctuation from natural energy source. PSCAD/EMTDC simulation is used to evaluate the performance of applied system configuration and control method.

  17. Simulation of offshore wind farm integrated into power grid using VSC HVDC system

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Hui; Nguyen, Mau Cuong; Rudion, Krzystof; Styczynski, Zbigniew Antoni [Magdeburg Univ. (Germany). Chair for Electric Power Networks and Renewable Energy Sources

    2011-07-01

    In this paper, the integration of an offshore wind farm into a power grid is studied based on the simulation of a developed test system including an aggregated DFIG wind farm model and VSC HVDC transmission system model. This paper concentrates on the transient stability and system performance with an applied controller for DFIG and HVDC converter stations. The results are obtained by simulation of the test system subjected to severe grid disturbance, e.g. three-phase short circuit fault at the point of common coupling (PCC). Furthermore, the conformity of the system performance with the current grid code, e.g. fault-ride through capability is investigated and confirmed from the simulation results. In addition, a DC-chopper circuit is modeled to protect the HVDC-link from the overvoltage without disconnection during grid faults. Different time delays of the DC-chopper are considered and simulated to investigate its influence on the system dynamics and performance. (orig.)

  18. A robust adaptive control with unmodeled dynamic for HVDC transmission systems

    Institute of Scientific and Technical Information of China (English)

    YAN Quan; LI Xing-yuan; WANG Lu; LIU Hong-chao; CHEN Shu-beng

    2006-01-01

    Utilizing the feature of quick response of HVDC to improve the performance of AC/DC system has become the emphasis to be researched.This paper introduces firstly the principle of the robust adaptive control of nonlinear systems with unmodeled dynamics,then developed the robust adaptive additional control of HVDC with unmodeled dynamics of generator in order to improve stability of power system.The additional control of HVDC with unmodeled dynamics only uses the local signals and its design is simple,furthermore it can obviously improve the stability of power system in different operational conditions.Experimental results using the presented concepts obtained on single machine infinite bus model are also included.These results prove the efficiency of the control scheme.The design process of controller provided a new idea to design controller by use of simplified model.

  19. Time domain responses of hydraulic bushing with two flow passages

    Science.gov (United States)

    Chai, Tan; Dreyer, Jason T.; Singh, Rajendra

    2014-02-01

    Hydraulic bushings are commonly employed in vehicle suspension and body sub-frame systems to control motion, vibration, and structure-borne noise. Since literature on this topic is sparse, a controlled bushing prototype which accommodates a combination of long and short flow passages and flow restriction elements is first designed, constructed and instrumented. Step-up and step-down responses of several typical fluid-filled bushing configurations are measured along with steady harmonic time histories of transmitted force and internal pressures. To analyze the experimental results and gain physical insights into the hydraulic bushing system, lumped system models of bushings with different design features are developed, and analytical expressions of transmitted force and internal pressure responses are derived by using the convolution method. Parametric studies are also conducted to examine the effect of hydraulic element parameters. System parameters are successfully estimated for both harmonic and step responses using theory and measurements, and the dynamic force measurements are analyzed using analytical predictions. Finally, some nonlinearities of the system are also observed, and the fluid resistance of flow passage is found to be the most nonlinear element.

  20. Digital controller for hybrid filter in HVDC based on approximate inverse system

    Institute of Scientific and Technical Information of China (English)

    SU Ling; ZHAO Dong-yuan; CHEN Jian-ye; WANG Zan-ji

    2006-01-01

    In order to eliminate the characteristic harmonics in high voltage direct current (HVDC) transmission systems and to simplify the analog controller structure,this paper proposes a new digital controller by adopting an approximate inverse system control strategy according to the frequency response characteristic of the hybrid power filter.The proposed digital controller is implemented with a TMS320C32 DSP,including a series of parallel digital band-pass filters,phase shifters and amplifiers.The results of both simulations based on PSCAD and experiments on a 30 kVA HVDC system prove that the proposed digital control system is stable and efficient for eliminating the harmonics.

  1. Small Signal Model for VSC-HVDC Connected DFIG-Based Offshore Wind Farms

    Directory of Open Access Journals (Sweden)

    Kai Liao

    2014-01-01

    Full Text Available Large-scale offshore wind farms are integrated with onshore ac grids through the voltage source converter based high voltage direct current (VSC-HVDC transmission system. The impact on the stability of the ac grids will be significant. The small signal model of a wind farm connected with voltage source converter based dc transmission system is studied in this paper. A suitable model for small signal stability analysis is presented. The control system of wind generator and the HVDC system has also been modeled in this model for small signal stability analysis. The impact of the control parameters on the network stability is investigated.

  2. Review of fault diagnosis and fault-tolerant control for modular multilevel converter of HVDC

    DEFF Research Database (Denmark)

    Liu, Hui; Loh, Poh Chiang; Blaabjerg, Frede

    2013-01-01

    This review focuses on faults in Modular Multilevel Converter (MMC) for use in high voltage direct current (HVDC) systems by analyzing the vulnerable spots and failure mechanism from device to system and illustrating the control & protection methods under failure condition. At the beginning......, several typical topologies of MMC-HVDC systems are presented. Then fault types such as capacitor voltage unbalance, unbalance between upper and lower arm voltage are analyzed and the corresponding fault detection and diagnosis approaches are explained. In addition, more attention is dedicated to control...

  3. Loss evaluation of HVAC and HVDC transmission solutions for large offshore wind farms

    Energy Technology Data Exchange (ETDEWEB)

    Negra, N. Barberis [Politecnico of Turin, Department of Electrical Engineering (Italy); Todorovic, J. [ELEKTROPRENOS, Banja Luka (Bosnia and Herzegovina); Ackermann, T. [Royal Institute of Technology, Teknikringen 33, 10044 Stockholm (Sweden)

    2006-07-15

    This paper presents a comparison of transmission losses for different technical transmission solutions for large offshore wind farms. Three technical solutions are analyzed, i.e. HVAC, HVDC Line Commutated Converter (LCC) and HVDC Voltage Source Converter (VSC). The losses for each technology are calculated for wind farms with different ratings and various distances to shore. In addition, solutions with combinations of two and the three different transmission technologies are analyzed and compared. Based on this comparison, further analysis regarding the economical feasibility can be performed in order to determine the most economic solutions for the transmission system of an offshore wind farm. (author)

  4. Power Flow Analysis of HVAC and HVDC Transmission Systems for Offshore WindParks

    DEFF Research Database (Denmark)

    da Silva, Filipe Miguel Faria; Castro, Rui

    2009-01-01

    As the onshore wind resource is running shorter, wind power promoters are paying attention to the offshore resources. As in most cases there is no load offshore, wind power must be transmitted to the main land. To do so, two options are available: HVAC and HVDC transmission systems. In this paper...... that HVAC solution is limited by the distance to shore and by the wind transmitted power. HVDC options do not show these limitations, but are more expensive and more delicate to deal with, because there is a lack of operational experience, so far....

  5. HVDC Solution for Offshore Wind Park Comprising Turbines Equipped with Full-Range Converters

    DEFF Research Database (Denmark)

    Sharma, Ranjan; Rasmussen, Tonny Wederberg; Jensen, Kim Høj

    2010-01-01

    of a HVDC transmission system. The power system under study includes an offshore wind farm comprising turbines equipped with full range converters. The collection network is a local AC grid. Power transmission is done through HVDC system. The grid side VSC (voltage source converter) controls the DC voltage...... a voltage drop is created at the collection grid, the wind turbines go into fault-ride-through mode. The power output from each of the wind turbines is thus reduced to balance the system power. The detailed explanation of the strategy is presented in the paper. Matlab simulation model was prepared and some...

  6. Operational characteristics analysis of a 8 mH class HTS DC reactor for an LCC type HVDC system

    Energy Technology Data Exchange (ETDEWEB)

    Kim, S. K.; Go, B. S.; Dinh, M. C.; Park, M.; Yu, I. K. [Changwon National University, Changwon (Korea, Republic of); Kim, J. H. [Daejeon University, Daejeon (Korea, Republic of)

    2015-03-15

    Many kinds of high temperature superconducting (HTS) devices are being developed due to its several advantages. In particular, the advantages of HTS devices are maximized under the DC condition. A line commutated converter (LCC) type high voltage direct current (HVDC) transmission system requires large capacity of DC reactors to protect the converters from faults. However, conventional DC reactor made of copper causes a lot of electrical losses. Thus, it is being attempted to apply the HTS DC reactor to an HVDC transmission system. The authors have developed a 8 mH class HTS DC reactor and a model-sized LCC type HVDC system. The HTS DC reactor was operated to analyze its operational characteristics in connection with the HVDC system. The voltage at both ends of the HTS DC reactor was measured to investigate the stability of the reactor. The voltages and currents at the AC and DC side of the system were measured to confirm the influence of the HTS DC reactor on the system. Two 5 mH copper DC reactors were connected to the HVDC system and investigated to compare the operational characteristics. In this paper, the operational characteristics of the HVDC system with the HTS DC reactor according to firing angle are described. The voltage and current characteristics of the system according to the types of DC reactors and harmonic characteristics are analyzed. Through the results, the applicability of an HTS DC reactor in an HVDC system is confirmed.

  7. Improved Power Flow Algorithm for VSC-HVDC System Based on High-Order Newton-Type Method

    Directory of Open Access Journals (Sweden)

    Yanfang Wei

    2013-01-01

    Full Text Available Voltage source converter (VSC based high-voltage direct-current (HVDC system is a new transmission technique, which has the most promising applications in the fields of power systems and power electronics. Considering the importance of power flow analysis of the VSC-HVDC system for its utilization and exploitation, the improved power flow algorithms for VSC-HVDC system based on third-order and sixth-order Newton-type method are presented. The steady power model of VSC-HVDC system is introduced firstly. Then the derivation solving formats of multivariable matrix for third-order and sixth-order Newton-type power flow method of VSC-HVDC system are given. The formats have the feature of third-order and sixth-order convergence based on Newton method. Further, based on the automatic differentiation technology and third-order Newton method, a new improved algorithm is given, which will help in improving the program development, computation efficiency, maintainability, and flexibility of the power flow. Simulations of AC/DC power systems in two-terminal, multi-terminal, and multi-infeed DC with VSC-HVDC are carried out for the modified IEEE bus systems, which show the effectiveness and practicality of the presented algorithms for VSC-HVDC system.

  8. 70 Bush Meat Trading in the Oban Hills Region of South-Eastern ...

    African Journals Online (AJOL)

    Choice-Academy

    2008-03-01

    Mar 1, 2008 ... and conservation of wildlife among the operators of bush meat trade and consumptive ... investigative carcass examination and bargaining to inspect and price bush meat. Results ..... are not matched with on the ground action.

  9. An Assessment of Converter Modelling Needs for Offshore Wind Power Plants Connected via VSC-HVDC Networks

    DEFF Research Database (Denmark)

    Glasdam, Jakob; Zeni, Lorenzo; Hjerrild, Jesper

    2013-01-01

    Modular multilevel cascaded converter (MMCC) based high voltage direct current (HVDC) transmission is technically superior to other technologies, especially in case of connection of offshore wind power plants (OWPPs). Modelling challenges are faced by OWPP developers, who are not acquainted...... with detailed information regarding the internal behaviour of such complex devices. This paper presents an investigation of the modelling requirements of the MMCC HVDC system, based on comparison between simulation results using a detailed HVDC representation in PSCAD/EMTDC and two less detailed models realised...

  10. L’économie américaine sous l’Administration Bush The US Economy under the Bush Administration

    Directory of Open Access Journals (Sweden)

    Frédéric Lambert

    2010-03-01

    Full Text Available Cet article dresse un bilan de la performance économique américaine au cours des huit années de la présidence Bush. Sous l’Administration Bush, et après une année de récession consécutive à l’éclatement de la « bulle internet », l’économie américaine a connu six années d’expansion. Cette expansion a été plus forte que dans les autres économies du G7, grâce notamment à une croissance plus élevée de la productivité et à une politique monétaire accommodante. Elle s’est néanmoins accompagnée d’un certain nombre de déséquilibres qui pesaient sur la situation dans les derniers mois de la présidence Bush.This article surveys the performance of the US economy over the eight years of the Bush Presidency. Under the Bush Administration and after a year of recession following the bursting of the internet bubble, the American economy enjoyed six years of expansion. This expansion was stronger than in the other G7 economies, thanks in particular to higher productivity growth and a very supportive monetary policy. However, it was the source of several imbalances which weighed on the situation as the Bush Presidency was drawing to a close.

  11. The Study on Hybrid Multi-Infeed HVDC System Connecting with Offshore Wind Farm

    DEFF Research Database (Denmark)

    Liu, Yan

    , a cooperative control of the VSC-HVDC system and a variable speed Squirrel Cage Induction Generator (SCIG)-based offshore wind farm is proposed. In the approach, an active power-frequency droop control is developed to achieve an autonomous reduction of the generated active powers from wind turbines, which thus...

  12. Frequency Regulation Strategies in Grid Integrated Offshore Wind Turbines via VSC-HVDC Technology: A Review

    Directory of Open Access Journals (Sweden)

    Jafar Jallad

    2017-08-01

    Full Text Available The inclusion of wind energy in a power system network is currently seeing a significant increase. However, this inclusion has resulted in degradation of the inertia response, which in turn seriously affects the stability of the power system’s frequency. This problem can be solved by using an active power reserve to stabilize the frequency within an allowable limit in the event of a sudden load increment or the loss of generators. Active power reserves can be utilized via three approaches: (1 de-loading method (pitching or over-speeding by a variable speed wind turbine (VSWT; (2 stored energy in the capacitors of voltage source converter-high voltage direct current (VSC-HVDC transmission; and (3 coordination of frequency regulation between the offshore wind farms and the VSC-HVDC transmission. This paper reviews the solutions that can be used to overcome problems related to the frequency stability of grid- integrated offshore wind turbines. It also details the permanent magnet synchronous generator (PMSG with full-scale back to back (B2B converters, its corresponding control strategies, and a typical VSC-HVDC system with an associated control system. The control methods, both on the levels of a wind turbine and the VSC-HVDC system that participate in a system’s primary frequency control and emulation inertia, are discussed.

  13. Investigation of multimodule buck–boost inverter-based HVDC transmission system

    Directory of Open Access Journals (Sweden)

    Ahmed A. Elserougi

    2015-01-01

    Full Text Available In high voltage direct current (HVDC systems, the semiconductor devices have to be connected in series to obtain the required high-voltage ratings. This study proposes a new HVDC configuration, namely, multimodule buck–boost inverter for HVDC transmission applications which avoids series connection of large number of semiconductor switches. In addition, it provides a blocking capability against DC side faults. The proposed configuration consists of several simple buck–boost converters which are assembled together to meet the requirements of high-voltage high-power applications. This paper studies the dynamic performance of the proposed system under different operating conditions, and the results were satisfactory. The main advantages of the proposed configuration are: (i pure sinusoidal output which minimises/eliminates the requirements for supplementary AC filters and offers an inherent suppression to the common mode voltages, (ii very low dv/dt stresses and (iii complete blocking capability of AC side contributions during DC side faults. This study discusses the system architecture, passive components selections, voltage and current ratings of its semiconductor devices and the required controllers. A comparison between the proposed configuration and other existing HVDC technologies is also presented in this study.

  14. Impacts of large-scale offshore wind farm integration on power systems through VSC-HVDC

    DEFF Research Database (Denmark)

    Liu, Hongzhi; Chen, Zhe

    2013-01-01

    the impacts of integrating a large-scale offshore wind farm into the transmission system of a power grid through VSC-HVDC connection. The concerns are focused on steady-state voltage stability, dynamic voltage stability and transient angle stability. Simulation results based on an exemplary power system...

  15. A generic inertia emulation controller for multi-terminal VSC-HVDC systems

    DEFF Research Database (Denmark)

    Zhu, Jiebei; Guerrero, Josep M.; Booth, Campbell;

    2013-01-01

    A generic Inertia Emulation Controller (INEC) for Multi-Terminal Voltage-source-converter based HVDC (VSC-MTDC) is proposed in this paper. The proposed INEC can be incorporated in any grid-side-voltage-source-converter (GVSC) station, allowing the MTDC terminal to contribute an inertial response...

  16. Design, Control, and Modeling of a New Voltage Source Converter for HVDC System

    Science.gov (United States)

    Mohan, Madhan; Singh, Bhim; Ketan Panigrahi, Bijaya

    2013-05-01

    Abstract: A New Voltage Source Converter (VSC) based on neutral clamped three-level circuit is proposed for High Voltage DC (HVDC) system. The proposed VSC is designed in a multipulse configuration. The converter is operated by Fundamental Frequency Switching (FFS). A new control method is developed for achieving all the necessary control aspects of HVDC system such as independent real and reactive power control, bidirectional real and reactive power control. The basic of the control method is varying the pulse width and by keeping the dc link voltage constant. The steady state and dynamic performances of HVDC system interconnecting two different frequencies network are demonstrated for active and reactive power control. Total number of transformers used in this system are reduced to half in comparison with the two-level VSCs for both active and reactive power control. The performance of the HVDC system is improved in terms of reduced harmonics level even at fundamental frequency switching. The harmonic performance of the designed converter is also studied for different value of the dead angle (β), and the optimized range of the dead angle is achieved for varying reactive power requirement. Simulation results are presented for the designed three level multipulse voltage source converters with the proposed control algorithm.

  17. Influence of current limitation on voltage stability with voltage sourced converter HVDC

    DEFF Research Database (Denmark)

    Zeni, Lorenzo; Jóhannsson, Hjörtur; Hansen, Anca Daniela;

    2013-01-01

    A first study of voltage stability with relevant amount of Voltage Sourced Converter based High Voltage Direct Current (VSC-HVDC) transmission is presented, with particular focus on the converters’ behaviour when reaching their rated current. The detrimental effect of entering the current...

  18. Connection of OWPPs to HVDC networks using VSCs and Diode Rectifiers: an Overview

    DEFF Research Database (Denmark)

    Saborío-Romano, Oscar; Bidadfar, Ali; Göksu, Ömer;

    This paper provides an overview of two technologies for connecting offshore wind power plants (offshore WPPs, OWPPs) to high-voltage direct current (HVDC) networks: voltage source converters (VSCs) and diode rectifiers (DRs). Current grid code requirements for the connection of such power plants...

  19. Coordinated Voltage Control in Offshore HVDC Connected Cluster of Wind Power Plants

    DEFF Research Database (Denmark)

    Sakamuri, Jayachandra N.; Rather, Zakir Hussain; Rimez, Johan;

    2016-01-01

    This paper presents a coordinated voltage control scheme (CVCS) for a cluster of offshore wind power plants (OWPPs) connected to a VSC HVDC system. The primary control point of the proposed voltage control scheme is the introduced Pilot bus, which is having the highest short circuit capacity...

  20. Dynamic Reactive Power Control in Offshore HVDC Connected Wind Power Plants

    DEFF Research Database (Denmark)

    Sakamuri, Jayachandra N.; Cutululis, Nicolaos Antonio; Rather, Zakir Hussain;

    2016-01-01

    This paper presents a coordinated reactive power control for a HVDC connected cluster of offshore wind power plants (WPPs). The reactive power reference for the WPP cluster is estimated by an optimization algorithm aiming at minimum active power losses in the offshore AC Grid. For each optimal...

  1. A Hybrid LCC-VSC HVDC Transmission System Supplying a Passive Load

    Science.gov (United States)

    Kotb, Omar

    High Voltage Direct Current (HVDC) transmission systems continue to be an excellent asset in modern power systems, mainly for their ability to overcome the problems of AC transmission, such as the interconnection of asynchronous grids, stability of long transmission lines, and use of long cables for power transmission. In the past 20 years, Voltage Source Converter (VSC)-HVDC transmission systems were developed and installed in many projects, thereby adding more operational benefits to DC transmission option, such as high controllability, ability to supply weak networks, and reduced converter reactive power demand. Nevertheless, VSC-HVDC transmission suffers from the disadvantages of high losses and cost. In this research, a hybrid HVDC employing a Line Commutated Converter (LCC) as rectifier and a VSC as inverter is used to supply a passive network through a DC cable. The hybrid system is best suited for unidirectional power transmission scenarios, such as power transmission to islands and remote load centers, where the construction of new transmission lines is prohibitively expensive. Control modes for the rectifier and inverter are selected and implemented using Proportional Integral (PI) controllers. Special control schemes are developed for abnormal operating conditions such as starting at light load and recovering from AC network faults. The system performance under steady state and transient conditions is investigated by EMTP-RV simulations. The results show the feasibility of the hybrid system.

  2. Fault Ride-through Capability Enhancement of VSC-HVDC-connected Offshore Wind Power Plants

    Institute of Scientific and Technical Information of China (English)

    Ranjan SHARMA; Qiuwei WU; Seung Tae CHA; Kim Høj ENSEN; Tony Wederberg RASMUSSEN; Jacob ØSTERGAARD

    2015-01-01

    To achieve active control of the AC voltage magnitude of wind power plant(WPP) collector network and improve the fault ride-through (FRT) capability,an FRT scheme based on feed forward DC voltage control is presented for voltage source converter-high voltage direct current(VSC-HVDC) connected offshore WPPs.During steady state operation,an open loop AC voltage control is implemented at the WPP-side VSC of the HVDC system so that any possible control interactions between WPP-side VSC and VSC of wind turbine are minimized.Whereas during any grid fault,a dynamic AC voltage reference is made according to both the DC voltage error and AC active current from the WPP collector system,thus ensuring fast and robust FRT of the VSC-HVDC-connected offshore WPPs.Under the unbalanced fault condition in the host power system,the resulting oscillatory DC voltage is directly used in the VSC AC voltage controller at the WPP side so that the WPP collector system voltage also reflects the unbalance in the main grid.Time domain simulations are performed to verify the efficacy of the FRT scheme based on the proposed feed forward DC voltage control.Simulation results show satisfactory FRT responses of the VSC-HVDC-connected offshore WPP under balanced and unbalanced faults in the host power system,as is shown under a serious fault in the WPP collector network.

  3. PowerFactory model for multi-terminal HVDC network with DC voltage droop control

    DEFF Research Database (Denmark)

    Korompili, Asimenia; Wu, Qiuwei

    Nowadays, most of the installed HVDC systems are based on line commutated converters (LCC), since this technology offers a series of advantages, mainly low costs and losses. However, voltage source converters (VSCs) have recently drawn more and more attention, due to their high controllability...

  4. A novel synthetic test system for thyristor level in the converter valve of HVDC power transmission

    Directory of Open Access Journals (Sweden)

    Liu Longchen

    2016-01-01

    Full Text Available The converter valve is the core equipment in the HVDC power transmission system, a+-nd its performance has a direct effect on the reliability, stability and efficiency of the whole power system. As the basic unit of HVDC converter valve, the thyristor level needs to be test routinely in order to grasp the state of the converter valve equipment. Therefore, it is urgent to develop a novel synthetic test system for the thyristor level with thyristor control unit (TCU. However, currently there is no specific test scheme for the thyristor level of HVDC converter valve. In this paper, the synthetic test principle, content and methods for the thyristor level with TCU are presented based on the analysis of the thyristor reverse recovery characteristic and the IEC technology standard. And a transient high-voltage pulse is applied to the thyristor level during its reverse recovery period in order to test the characteristics of thyristor level. Then, the synthetic test system for the thyristor level is applied to the converter valve test of ±800 kV HVDC power transmission project, and the practical test result verifies the reasonability and validity of the proposed synthetic test system.

  5. Modelling and Simulation of VSC-HVDC Connection for Offshore Wind Power Plants

    DEFF Research Database (Denmark)

    Chaudhary, Sanjay Kumar; Teodorescu, Remus; Rodriguez, Pedro

    2010-01-01

    Several large offshore wind power plants (WPP) are planned in the seas around Europe. VSC-HVDC is a suitable means of integrating such large and distant offshore WPP which need long submarine cable transmission to the onshore grid. Recent trend is to use large wind turbine generators with full...

  6. Automatic Generation Control in Multi Area Interconnected Power System by using HVDC Links

    Directory of Open Access Journals (Sweden)

    Yogendra Arya

    2012-01-01

    Full Text Available This paper investigates the effects of HVDC link in parallel with HVAC link on automatic generation control (AGC problem for a multi-area power system taking into consideration system parameter variations. A fuzzy logic controller is proposed for four area power system interconnected via parallel HVAC/HVDC transmission link which is also referred as asynchronous tie-lines. The linear model of HVAC/HVDC link is developed and the system responses to sudden load change are studied. The simulation studies are carried out for a four area interconnected thermal power system. Suitable solution for automatic generation control problem of four area electrical power system is obtained by means of improving the dynamic performance of power system under study. Robustness of controller is also checked by varying parameters. Simulation results indicate that the scheme works well. The dynamic analyses have been done with and without HVDC link using fuzzy logic controller in Matlab-Simulink. Further a comparison between the two is presented and it has been shown that the performance of the proposed scheme is superior in terms of overshoot and settling time.

  7. Modern Travelling Wave Based Fault Location Techniques for HVDC Transmission Lines

    Institute of Scientific and Technical Information of China (English)

    CHEN Ping; XU Bingyin; LI Jing; GE Yaozhong

    2008-01-01

    The modern travelling wave based fault location principles for transmission lines are ana-lyzed. In order to apply the travelling wave principles to HVDC transmission lines, the special tech-nical problems are studied. Based on this, a fault locating system for HVDC transmission lines is developed. The system can support modern double ended and single ended travelling wave princi-ples simultaneously, and it is composed of three different parts: travelling wave data acquisition and processing system, communication network and PC based master station. In the system, the fault generated transients are induced from the ground leads of the over-voltage suppression ca-pacitors of an HVDC line through specially developed travelling wave couplers.The system was applied to 500 Kv Gezhouba-Nanqiao(Shanghai)HVDC transmission line in China. Some field op- eration experiences are summarized, showing that the system has very high reliability and accu- racy,and the maximum location error is about 3 km(not more than 0.3% of the total line length). Obviously, the application of the system is successful, and the fault location problem has finally been solved completely since the line operation.

  8. 500-kV HVDC air-blast circuit breaker. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Bachman, B.; Ruoss, E.

    1986-08-01

    This report describes the first HVDC circuit breaker to be tested on a full-scale utility system. Modular in construction to ensure economic feasibility, this breaker has a standard ac air-blast breaker as its main component and interrupts current up to 2200-A dc.

  9. Harmonic Stability Studies in VSC-HVDC Grid Connected Offshore Wind Power Plants

    DEFF Research Database (Denmark)

    Glasdam, Jakob Bærholm; Gevorgian, Vahan; Bak, Claus Leth

    2017-01-01

    the harmonic instability phenomena in HVDC grid connected OWPPs using both frequency and time domain simulations. A good correlation at lower frequencies between the two domains is observed. However, the frequency domain is insufficient at higher frequencies (i.e. in the vicinity of the switching frequency...

  10. Novel control strategies of HVDC system with self-commutated converter. Jireishiki henkanki wo tekiyoshita HVDC sytem ni okeru tanshi seigyo to kyocho seigyo

    Energy Technology Data Exchange (ETDEWEB)

    Tokiwa, Y.; Ichikawa, F.; Suzuki, K. (Tokyo Electric Power Co. Inc., Tokyo (Japan)); Inokuchi, H.; Hirose, S.; Kimura, K. (Toshiba Corp., Tokyo (Japan))

    1992-01-20

    This report describes new control strategies of a self -commutated converter applied to the HVDC systems; that is, the cooperative control for a two-terminal transmission system and the terminal control which is applicable to a multi-terminal system. The DC voltage control with an upper and lower power-limiter showed excellent characteristics when applied to the two- terminal transmission system. A voltage margin method was also introduced as a power flow reversal method. These terminal control methods, if required, are able to change interchange power at the receiving end in the case of fault in the communication system. Moreover, the DC voltage control with two-stage voltage control characteristics was proposed for the multi-terminal HVDC system. with this mehtod, the DC transmission system can be operated continuously and stably cooperating electric power at each terminal even when one terminal is collapsed. The terminal control performance in the above two-terminal HVDC system was tested with a simulator. The result showed favorable performance characteristics at the time of power flow reversal and one terminal start-up during other terminal operation. 5 refs., 16 figs.

  11. The Invasive Shrub, Buddleja davidii (Butterfl y Bush)

    Science.gov (United States)

    Buddleja davidii Franchet (Synonym. Buddleia davidii; common name Butterfly bush) is a perennial, semi-deciduous shrub or small multi-stemmed tree that is resident in gardens and disturbed areas in temperate locations worldwide. Since its introduction to the United Kingdom from c...

  12. Hyperelastic Modelling and Finite Element Analysing of Rubber Bushing

    Directory of Open Access Journals (Sweden)

    Merve Yavuz ERKEK

    2015-03-01

    Full Text Available The objective of this paper is to obtain stiffness curves of rubber bushings which are used in automotive industry with hyperelastic finite element model. Hyperelastic material models were obtained with different material tests. Stress and strain values and static stiffness curves were determined. It is shown that, static stiffness curves are nonlinear. The level of stiffness affects the vehicle dynamics behaviour.

  13. Bush annab kinga kindralitele Iraagis, vahetub ka luurejuht / Kaivo Kopli

    Index Scriptorium Estoniae

    Kopli, Kaivo

    2007-01-01

    Vaatlejate hinnangul esitab president Bush uue Iraagi-strateegia, mis näeb ette lisaks kuni 20 000 sõjaväelase Iraaki saatmist ning muudatusi sõjalises juhtkonnas. Ametist lahkuvad Iraagis vägesid juhatav kindral George Casey ning Iraagi ja Afganistani operatsioonide üldjuht John Abizaid

  14. Bush kutsub ühte hoidma / Kaivo Kopli

    Index Scriptorium Estoniae

    Kopli, Kaivo

    2004-01-01

    USA president George W. Bush kutsus liitlasriike hoidma oma väeüksusi Iraagis. Hispaania tulevane peaminister Jose Luis Rodriquez Zapatero lubas Hispaania sõjaväelased Iraagist ära tuua, kui operatsioonide juhtimine ei lähe USA-lt üle ÜRO-le. Vt. samas: Rumsfeld: hispaanlaste asemele tulevad teised

  15. Budgets come first as Bush chooses NASA head

    CERN Multimedia

    Schrope, M

    2001-01-01

    President Bush has nominated a budget expert with no aerospace or scientific background as the agency's administrator. Sean O'Keefe, formerly scrutinized overspending in the International Space Station programme. If appointed, he will have to implement reforms he himself recommended (1/2 page).

  16. President Bush: A Friend of Higher Education after All?

    Science.gov (United States)

    Basken, Paul

    2008-01-01

    President Bush's proposals on such topics as toughening accreditation standards and limiting the use of human embryonic stem cells in research may not have made him popular in academe over his two terms. This article reports that the president's willingness to spend federal money on many of colleges' top priorities might improve the perception of…

  17. The Gore/Bush Records on Higher Education.

    Science.gov (United States)

    Walters, Ronald

    2000-01-01

    Compares the records of presidential candidates George W. Bush and Al Gore on higher education issues and, specifically, those of interest to the Black community. Concludes that Al Gore's record makes him an overall better choice in the 2000 campaign. (DB)

  18. Bush kutsub ühte hoidma / Kaivo Kopli

    Index Scriptorium Estoniae

    Kopli, Kaivo

    2004-01-01

    USA president George W. Bush kutsus liitlasriike hoidma oma väeüksusi Iraagis. Hispaania tulevane peaminister Jose Luis Rodriquez Zapatero lubas Hispaania sõjaväelased Iraagist ära tuua, kui operatsioonide juhtimine ei lähe USA-lt üle ÜRO-le. Vt. samas: Rumsfeld: hispaanlaste asemele tulevad teised

  19. BUDDLEJA DAVIDII (BUTTERFLY BUSH): A GROWING THREAT TO RIPARIA?

    Science.gov (United States)

    Buddleja davidii, an Asian shrub or small tree (family Buddlejaceae; commonly referred to as Butterfly bush) is found in the United States, New Zealand, Australia, and Europe as a popular ornamental and an aggressive invasive that has become widespread in floodplains, riverbeds, ...

  20. Expanding the Black Woman's Horizon: Picking From a Higher Bush ...

    African Journals Online (AJOL)

    Expanding the Black Woman's Horizon: Picking From a Higher Bush Motif in Zora ... While bringing up Janie, Nanny overprotects her and shields her from the ... In her quest, Janie discovers that it is not comfort or money that brings about love ...

  1. Naftahind tõusis ja Bush langes / Heiki Suurkask

    Index Scriptorium Estoniae

    Suurkask, Heiki, 1972-

    2005-01-01

    Tagasivaates 2005. aastale nimetab autor aasta tõusjad: need on naftahind, heategevus ja annetamine loodusõnnetustes kannatanutele, revolutsioonid. Aasta langejad on tema hinnangul USA president George W. Bush ning Vene hävitaja allakukkumine Leedu kohal. Ka on tema sõnul pisut pidurdunud EL-i hoog

  2. Oliver Stone : "Bush oli paadialune!" / Oliver Stone ; interv. Margit Tõnson

    Index Scriptorium Estoniae

    Stone, Oliver

    2008-01-01

    Kreekas, Thessaloniki filmifestivalil antud intervjuu. Festivalil linastus režissööri mängufilm "W", mille peaosas George Bush jun. (mängib Josh Brolin). Lisaks filmist : ""W" - ümbersündinud mehe kentsakas portree"

  3. Oliver Stone : "Bush oli paadialune!" / Oliver Stone ; interv. Margit Tõnson

    Index Scriptorium Estoniae

    Stone, Oliver

    2008-01-01

    Kreekas, Thessaloniki filmifestivalil antud intervjuu. Festivalil linastus režissööri mängufilm "W", mille peaosas George Bush jun. (mängib Josh Brolin). Lisaks filmist : ""W" - ümbersündinud mehe kentsakas portree"

  4. Parasitoid pressure and the radiation of a gallforming group (Cecidomyiidae: Asphondylia spp.) on creosote bush (Larrea tridentata).

    Science.gov (United States)

    Waring, G L; Price, P W

    1989-05-01

    We tested the Enemy Impact Hypothesis, which predicts that communities of one tropic level are organized by the tropic level above. In the case of gallforming insect communities, the hypothesis predicts that gall morphology will diverge, minimizing the number of parasitoids shared among species. We used the monophyletic group of gallforming cecidomyiids (Asphondylia spp.) on creosote bush (Larrea tridentata) to test this hypothesis, predicting that species with thicker gall walls should exclude species of parasitoids with shorter ovipositors and have lower levels of parasitism. Of 17 parasitoid species reared from Asphondylia galls on creosote bush, 9 accounted for over 98% of parasitism. Seven of these 9 species had ovipositors long enough to penetrate 10 of 13 gall morphs measured. There was no significant relationship between gall wall thickness and number of associated parasitoid species (r (2)=0.01, P>0.05, n=13). There was no relationship between gall wall thickness and types of parasitoid species colonizing galls: parasitoids with the shortest ovipositors colonized all types of gall morphs and were dominant members of the parasitoid assemblages in galls with the thickest walls. Ultimately, there were no significant differences in percent parasitism among Asphondylia species, regardless of gall wall thickness. We found no difference in numbers of associated parasitoids or percent parasitism in galls with different textures (e.g. hairy versus smooth), different locations on the plant or different phenologies. Our results suggest that enemy impact has not influenced the diversity of this gall community. Gall wall thickness, phenology, location on the plant and surface structure do not appear to influence the distribution of parasitoid species. Other explanations are offered to account for diversity in gall morphology among these species.

  5. Power Hardware In The Loop Validation of Fault Ride Through of VSC HVDC Connected Offshore Wind Power Plants

    DEFF Research Database (Denmark)

    Sharma, Ranjan; Wu, Qiuwei; Cha, Seung-Tae;

    2014-01-01

    This paper presents the power hardware in the loop (PHIL) validation of a feed forward DC voltage control scheme for the fault ride through (FTR) of voltage source converter (VSC) high voltage DC (HVDC) connected offshore wind power plants (WPPs). In the proposed FRT scheme, the WPP collector...... network AC voltage is actively controlled by considering both the DC voltage error and the AC current from the WPP AC collector system which ensures fast and robust FRT of the VSC HVDC connected offshore WPPs. The PHIL tests were carried out in order to verify the efficacy of the proposed feed forward DC...... voltage control scheme for enhancing the FRT capability of the VSC HVDC connected WPPs. The PHIL test results have demonstrated the proper control coordination between the offshore WPP and the WPP side VSC and the efficient FRT of the VSC HVDC connected WPPs....

  6. Sliding Mode Control of Three Levels Back-To-Back VSC-HVDC System Using Space Vector Modulation

    Directory of Open Access Journals (Sweden)

    Bouafia Saber

    2014-03-01

    Full Text Available In this study, a sliding mode strategy proposed to control a three levels Back-to-Back High Voltage Direct Current (HVDC system based on the three-level voltage source converter (VSC. The voltage-balancing control of two split DC capacitors of the VSC-HVDC system is achieved using three-level space vector modulation with balancing strategy based on the effective use of the redundant switching states of the inverter voltage vectors. Finally, a complete simulation of the VSC-HVDC system validates the efficiency of the proposed strategy law. Compared to the conventional control, Sliding Mode Control scheme for the VSC-HVDC system shows the attractive advantages such as offering high tracking accuracy, fast dynamic response and good robustness.

  7. Application of the Finite Element Method in the Glass Fiber Bushing Research

    Institute of Scientific and Technical Information of China (English)

    CHEN Song; LU Jiansheng; GUAN Weiming; ZHANG Kunhua; PAN Yong; TAN Zhilong; XIA Lu

    2012-01-01

    Design and optimization of bushing at present mainly use the traditional experience method.The relevant research that adopts computer simulation to carry on the operation behavior of the bushing has appeared in recent years.How to use the finite element method to research bushing was introduced in the article.Physics fields and many relevant parameters of one real bushing were calculated.Through the results of calculation,it indicate that the finite element method is very useful in bushing research of designing and optimizing.

  8. Bush doctrine in the Middle East; The US foreign policy towards the Middle East during the George W. Bush presidency

    Directory of Open Access Journals (Sweden)

    Lukáš Hoder

    2011-06-01

    Full Text Available The article is focused at the most important elements of the US foreign policy towards the Middle East during the administration of George W. Bush (2001 – 2009. The text has two parts. The first part shows three important influences on creation and formulation of the US foreign policy towards the region. At the first place it was an effort to preserve unipolar character of the international system, hegemonic possition of the USA and its dominance in all regions. The second source was specific decision-making process set up by president Bush and the third source of the Bush strategy was a partial transformation of the US longtime policy towards the Middle East. The second part of the article discuss results of the Bush doctrine in the region. The text is focused at five most important consequences of the US foreign policy, which are the fight against proliferation of weapons of mass destruction, the pursuit of the democratization throughout the region, the Israel-Palestinian conflict, regional “cold war” between Iran and Saudi Arabia and finally the struggle to stabilize the post-conflict Iraq.

  9. The Impact Study of a Statcom on Commutation Failures in an HVDC Inverter Feeding a Weak AC System

    Science.gov (United States)

    Khatir, Mohamed; Zidi, Sid-Ahmed; Fellah, Mohammed-Karim; Hadjeri, Samir; Flitti, Mohamed

    2012-03-01

    The Static Synchronous Compensator (STATCOM) devices are pure power electronics devices that use voltage source, IGBT, IGCT or GTO based converters to generate reactive current. This paper illustrates the effect of STATCOM connected whit an HVDC inverter feeding a weak AC network, on the recovery from commutation failures following AC side disturbances. MATLAB/SIMULINK simulation results have demonstrated the robust performance of the proposed system based on the first CIGRÉ HVDC Benchmark model against commutation failures.

  10. Comparative study of high voltage bushing designs suitable for apparatus containing cryogenic helium gas

    Science.gov (United States)

    Rodrigo, H.; Graber, L.; Kwag, D. S.; Crook, D. G.; Trociewitz, B.

    2013-10-01

    The high voltage bushing forms a critical part of any termination on cables, transformers and other power system devices. Cryogenic entities such as superconducting cables or fault current limiters add more complexity to the design of the bushing. Even more complex are bushings designed for superconducting devices which are cooled by high pressure helium gas. When looking for a bushing suitable for dielectric cable tests in a helium gas cryostat no appropriate device could be found that fulfilled the criterion regarding partial discharge inception voltage level. Therefore we decided to design and manufacture a bushing in-house. In the present work we describe the dielectric tests and operational experience on three types of bushings: One was a modified commercially available ceramics feed through which we adopted for our special need. The second bushing was made of an epoxy resin, with an embedded copper squirrel cage arrangement at the flange, extending down about 30 cm into the cold end of the bushing. This feature reduced the electric field on the surface of the bushing to a negligible value. The third bushing was based on a hollow body consisting of glass fiber reinforced polymer and stainless steel filled with liquid nitrogen. The measurements showed that the dielectric quality of all three bushings exceeded the requirements for the intended purpose. The partial discharge (PD) data from these studies will be used for the design and fabrication of a cable termination for a specialized application on board a US Navy ship.

  11. Anisotropy in Alpedrete granite cutting (Rift, Grain and Hardway directions) and effect on bush hammered heritage ashlars

    Science.gov (United States)

    Freire-Lista, David Martin; Fort, Rafael

    2015-04-01

    has been used preferably as wall façades in heritage building ashlars. That is, the ashlars exposed surface. In other words, the exfoliation microcracks are oriented vertically in heritage ashlars. R planes bush hammering produces many new microcracks and propagation of exfoliation microcracks, generating significant decay with parallel and oblique microcracks to the bush hammered surface to a depth of more than 10 mm. G and H planes bush hammering generates coalescence and increased length of intra-crystalline exfoliation microcracks in the R plane; although, with less generation of new microcracks and less surface decay. To understand the decay in bush hammered granite ashlars and sculptures it is essential to study the orientation and distribution of exfoliations microcracks, which follow the R orientation stone in the quarry. This orientation should be reproduced when performing artificial accelerated ageing tests, especially with stones used in heritage buildings. Acknowledgements This study was funded by the Community of Madrid under the GEOMATERIALS 2 project (S2013/MIT-2914). The authors are members of the Complutense University of Madrid's Research Group: 'Alteración y Conservación de los Materiales Pétreos del Patrimonio' (ref. 921349)

  12. A novel power control strategy of Modular Multi-level Converter in HVDC-AC hybrid transmission systems for passive networks

    DEFF Research Database (Denmark)

    Hu, Zhenda; Wu, Rui; Yang, Xiaodong;

    2014-01-01

    With the development of High Voltage DC Transmission (HVDC) technology, there will be more and more HVDC-AC hybrid transmission system in the world. A basic challenge in HVDC-AC hybrid transmission systems is to optimize the power sharing between DC and AC lines, which become more severe when...... supplying power for passive networks, as the surplus power can only flow back to power grids through the AC lines. To deal with this issue, it demands not only accurate system capability design but also flexible power control strategy of power converters in VSC-HVDC. This paper proposes a novel power...

  13. Feasibility analysis of a novel hybrid-type superconducting circuit breaker in multi-terminal HVDC networks

    Science.gov (United States)

    Khan, Umer Amir; Lee, Jong-Geon; Seo, In-Jin; Amir, Faisal; Lee, Bang-Wook

    2015-11-01

    Voltage source converter-based HVDC systems (VSC-HVDC) are a better alternative than conventional thyristor-based HVDC systems, especially for developing multi-terminal HVDC systems (MTDC). However, one of the key obstacles in developing MTDC is the absence of an adequate protection system that can quickly detect faults, locate the faulty line and trip the HVDC circuit breakers (DCCBs) to interrupt the DC fault current. In this paper, a novel hybrid-type superconducting circuit breaker (SDCCB) is proposed and feasibility analyses of its application in MTDC are presented. The SDCCB has a superconducting fault current limiter (SFCL) located in the main current path to limit fault currents until the final trip signal is received. After the trip signal the IGBT located in the main line commutates the current into a parallel line where DC current is forced to zero by the combination of IGBTs and surge arresters. Fault simulations for three-, four- and five-terminal MTDC were performed and SDCCB performance was evaluated in these MTDC. Passive current limitation by SFCL caused a significant reduction of fault current interruption stress in the SDCCB. It was observed that the DC current could change direction in MTDC after a fault and the SDCCB was modified to break the DC current in both the forward and reverse directions. The simulation results suggest that the proposed SDCCB could successfully suppress the DC fault current, cause a timely interruption, and isolate the faulty HVDC line in MTDC.

  14. 混合双馈入直流系统中VSC-HVDC对LCC-HVDC受端系统强度的影响%The Effects of VSC-HVDC on the System Strength of LCC-HVDC in Dual-infeed Hybrid HVDC System

    Institute of Scientific and Technical Information of China (English)

    倪晓军; 赵成勇; 郭春义; 刘羽超

    2015-01-01

    为了准确评估混合双馈入直流系统中电网换相换流器高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)子系统的受端系统强度,对LCC-HVDC 子系统的有效短路比进行研究。第一,基于牛顿最优潮流算法,分析混合双馈入直流系统中电压源换流器高压直流输电(voltage source converter based HVDC, VSC-HVDC)子系统采用不同的功率输送方向和控制方式时,对LCC-HVDC子系统的交流系统电压支撑强度的影响关系。第二,计算VSC-HVDC子系统的等效阻抗,提出能够有效评估混合双馈入系统中LCC-HVDC子系统有效短路比的等值有效短路比指标。利用该指标可将混合双馈入直流系统中LCC-HVDC子系统等效为受端交流系统电压支撑强度与之相同的单馈入直流输电系统。最后,基于 PSCAD/ EMTDC进行仿真分析,仿真结果证明了VSC-HVDC对LCC-HVDC 子系统影响关系的正确性以及等值有效短路比指标的有效性。%The effective short circuit ratio of line commutated converter based high voltage direct current (LCC-HVDC) sub-system in dual-infeed hybrid HVDC system was investigated to evaluate the system strength of LCC-HVDC. Firstly, the voltage support strength of AC system was analyzed when different power flow directions and different controled strategies were adopted in voltage source converter (VSC) based on optimal power flow by Newton approach. Secondly, the equivalent impedance of VSC-HVDC was calculated, and the effective short circuit ratio of the LCC-HVDC was quantified by a proposed “equivalent effective short circuit ratio” index. The LCC-HVDC in dual-infeed hybrid HVDC system could be equivalent to a single-infeed HVDC system which had the same voltage support strength by the index. Simulation results in PSCAD/EMTDC show that the analysis on the effects of VSC-HVDC to LCC-HVDC proved to be accurate and the “equivalent effective short circuit ratio” index is

  15. Diversity of intersegmental auditory neurons in a bush cricket.

    Science.gov (United States)

    Stumpner, Andreas; Molina, Jorge

    2006-12-01

    Various auditory interneurons of the duetting bush cricket Ancistrura nigrovittata with axons ascending to the brain are presented. In this species, more intersegmental sound-activated neurons have been identified than in any other bush cricket so far, among them a new type of ascending neuron with posterior soma in the prothoracic ganglion (AN4). These interneurons show not only morphological differences in the prothoracic ganglion and the brain, but also respond differently to carrier frequencies, intensity and direction. As a set of neurons, they show graded differences for all of these parameters. A response type not described among intersegmental neurons of crickets and other bush crickets so far is found in the AN3 neuron with a tonic response, broad frequency tuning and little directional dependence. All neurons, with the exception of AN3, respond in a relatively similar manner to the temporal patterns of the male song: phasically to high syllable repetitions and rhythmically to low syllable repetitions. The strongest coupling to the temporal pattern is found in TN1. In contrast to behavior the neuronal responses depend little on syllable duration. AN4, AN5 and TN1 respond well to the female song. AN4 (at higher intensities) and TN1 respond well to a complete duet.

  16. Feasibility analysis of a novel hybrid-type superconducting circuit breaker in multi-terminal HVDC networks

    Energy Technology Data Exchange (ETDEWEB)

    Khan, Umer Amir [Hanyang University, Sa-3dong, Sangrok-gu, Ansan 426-791 (Korea, Republic of); National University of Sciences and Technology, PNEC Campus, Habib Rehmatullah Road, Karachi (Pakistan); Lee, Jong-Geon; Seo, In-Jin [Hanyang University, Sa-3dong, Sangrok-gu, Ansan 426-791 (Korea, Republic of); Amir, Faisal [National University of Sciences and Technology, PNEC Campus, Habib Rehmatullah Road, Karachi (Pakistan); Lee, Bang-Wook, E-mail: bangwook@hanyang.ac.kr [Hanyang University, Sa-3dong, Sangrok-gu, Ansan 426-791 (Korea, Republic of)

    2015-11-15

    Highlights: • A novel hybrid-type superconducting circuit breaker (SDCCB) is proposed. • SDCCB has SFCL located in the main current path to limit the fault current until the final trip signal. • SFCL in SDCCB suppressed the fast rising DC fault current for a predefined time. • SFCL significantly reduced the DC current breaking stress on SDCCB components. • SDCCB isolated the HVDC faulty line in three, four, and five converter stations MTDC. - Abstract: Voltage source converter-based HVDC systems (VSC-HVDC) are a better alternative than conventional thyristor-based HVDC systems, especially for developing multi-terminal HVDC systems (MTDC). However, one of the key obstacles in developing MTDC is the absence of an adequate protection system that can quickly detect faults, locate the faulty line and trip the HVDC circuit breakers (DCCBs) to interrupt the DC fault current. In this paper, a novel hybrid-type superconducting circuit breaker (SDCCB) is proposed and feasibility analyses of its application in MTDC are presented. The SDCCB has a superconducting fault current limiter (SFCL) located in the main current path to limit fault currents until the final trip signal is received. After the trip signal the IGBT located in the main line commutates the current into a parallel line where DC current is forced to zero by the combination of IGBTs and surge arresters. Fault simulations for three-, four- and five-terminal MTDC were performed and SDCCB performance was evaluated in these MTDC. Passive current limitation by SFCL caused a significant reduction of fault current interruption stress in the SDCCB. It was observed that the DC current could change direction in MTDC after a fault and the SDCCB was modified to break the DC current in both the forward and reverse directions. The simulation results suggest that the proposed SDCCB could successfully suppress the DC fault current, cause a timely interruption, and isolate the faulty HVDC line in MTDC.

  17. Grid Integration of Offshore Wind Farms via VSC-HVDC – Dynamic Stability Study

    DEFF Research Database (Denmark)

    Liu, Hongzhi

    -HVDC transmission are addressed. The main objectives have been to study the dynamic interactions between offshore wind farms and interconnected power systems, pinpoint the impact on the electrical grid while integrating large-scale offshore wind farms via VSC-HVDC link and propose potential solutions to improve......, may not be able to respond to the onshore grid frequency excursion in time. Consequently, the stability and security of power system will be put at risk, especially for those with high wind penetration. A coordinated frequency control scheme is developed not only to reduce the responding latency...... fluctuation mitigation. A new converter rating evaluation approach as well as a new power management strategy is proposed to enable the BESS to enhance the system frequency response on the basis of wind power fluctuation mitigation....

  18. Research of Bipolar HVDC Transmission Lines Based on Traveling Wave Differential Protection

    Directory of Open Access Journals (Sweden)

    Baina He

    2013-07-01

    Full Text Available The principle of the traveling wave based differential protection for bipolar HVDC transmission lines is proposed in the paper. Unlike the traditional current differential protection, the quantity of current is replaced by the quantity of the traveling wave for comparison. The traveling wave at the remote end is transferred to the local end for comparison to the local traveling wave. For the bipolar DC transmission lines, the polar-mode (aerial mode traveling waves are employed to establish the discriminative criterion. The ground-mode traveling waves are utilized for faulty line detector for bipolar operation modes. The entire protection scheme is simulated in PSCAD/EMTDC associated with the standard ±500kV HVDC transmission system. The simulation results show that the new protection has the advantages of higher sensitivity, reliability and security. The fault resistance can be coverd by the traveling wave based differential protection reaches to 500 Ohm.    

  19. Robust Global Control Strategies for Improvement of Angular Stability using FACTS and HVDC Devices

    Science.gov (United States)

    Agnihotri, P.; Kulkarni, A. M.; Gole, A. M.

    2013-05-01

    System-wide feedback signals made available by Wide-Area Measurement Systems technology can be used in FACTS/HVDC based controllers for the improvement of angular stability. These global signals can facilitate the efficient use of controller effort to stabilize critical swing modes. This paper introduces a restricted global strategy which involves the use of specific global feedback signals which are available at the HVDC/FACTS locations. The strategy is expected to be robust to changes in the power grid as well as communication uncertainties. This paper presents a heuristic introduction to this strategy using a circuit analogy of a simplified model of a power system. Preliminary results on a small system are also presented.

  20. Wide-Area Robust Decentralized Coordinated Control of HVDC Power System Based on Polytopic System Theory

    Directory of Open Access Journals (Sweden)

    Shiyun Xu

    2015-01-01

    Full Text Available The present study proposes a hierarchical wide-area decentralized coordinated control framework for HVDC power system that is robust to multiple operating conditions. The upper level wide-area coordinated controller is designed in the form of dynamic output feedback control that coordinates the lower level HVDC supplementary controller, PSS, and SVC. In order to enhance the robustness of the designed controller under various operating conditions, the polytopic model is introduced such that the closed-loop control system can be operated under strong damping mode in virtue of the stability criterion based on damping ratio. Simulation results demonstrate that the proposed controller design algorithm is capable of enhancing the system damping over four different conditions.

  1. Tailored sPP/Silica Nanocomposite for Ecofriendly Insulation of Extruded HVDC Cable

    Directory of Open Access Journals (Sweden)

    Bin Dang

    2015-01-01

    Full Text Available Cross-linked polyethylene (XLPE is a thermosetting material that cannot be recycled at the end of its lifetime. This study investigated the potential of syndiotactic polypropylene (sPP/silica as an ecofriendly extruded insulation system for HVDC cables. We investigated the morphology, Fourier transform infrared, and thermal, thermomechanical, and electrical behaviors of sPP modified with 0.5–3% nanosilica. We found that the silica/sPP nanocomposite without cross-linking offered a suitable mechanical modulus at room temperature and sufficient intensity at high temperatures, and adding nanosilica modified by a silane coupling agent to the sPP resulted in significant DC resistivity and space charge improvement. The optimal nanosilica content in the sPP was determined by balancing the mechanical and thermomechanical characteristics and the DC resistivity. The sPP/silica nanocomposite reported here shows great potential as a candidate insulation material for future ecofriendly extruded HVDC cables.

  2. Harmonic Analysis of VSC-HVDC%VSC-HVDC的谐波分析

    Institute of Scientific and Technical Information of China (English)

    胡弢

    2009-01-01

    基于电压源换流器的高压直流输电技术(VSC-HVDC)已经在电力系统中得到了应用.针对采用双闭环解耦控制的VSC-HVDC,对其谐渡产生机理进行了详细的理论分析和数学推导,并针对分析结果提出了变调制度的谐波抑制措施:通过Matlab/Simulink(建立了VSC-HVDC供电有源系统的仿真模型,仿真结果验证了理论分析的正确性和谐波抑制措施的有效性.

  3. Power system analysis of Hanlim superconducting HVDC system using real time digital simulator

    Science.gov (United States)

    Won, Y. J.; Kim, J. G.; Kim, A. R.; Kim, G. H.; Park, M.; Yu, I. K.; Sim, K. D.; Cho, J.; Lee, S.; Jeong, K. W.; Watanabe, K.

    2011-11-01

    Jeju island is located approximately 100 km south from the mainland of Korea, and had a peak load of about 553 MW in 2008. The demand increases 7.2% a year over the last 5 years. Since the wind profiles of Jeju island are more favorable than mainland of Korea, many companies have shown interest in the wind power business at the Jeju island. Moreover KEPCO has a plan for renewable energy test too whose power will be delivered by HVDC system. One kilometer length of total 8 km was designed as superconducting DC cable. Rest 7 km will be the conventional overhead line. In this paper, the authors have developed a simulation model of the power network around 8 km HVDC system using real time digital simulator (RTDS).

  4. Dynamic modelling of VSC-HVDC for connection of offshore wind farms

    DEFF Research Database (Denmark)

    Rios, Bardo; Garcia-Valle, Rodrigo

    2011-01-01

    A VSC-HVDC (Voltage Source Converter – High Voltage Direct Current) dynamic model with a set of control strategies is developed in DIgSILENT Power-Factory with the objective of analyzing the converter’s operating capability for grid support during grid faults. The investigation is carried out based...... on a 165 MW offshore wind farm with induction generators and a Low Voltage Ride-Through solution of the offshore wind turbines and Static Voltage Compensator units in the point of connection with a grid represented by a reduced four-generator power grid model. VSC-HVDC promises to be a reliable alternative...... solution for interconnection with off-shore wind farms as they become larger, with a higher installed power capacity, increased number of wind turbines, and geographically situated at larger distances from suitable connection points in the transmission grids....

  5. Modelling and Simulation of VSC-HVDC Connection for Wind Power Plants

    DEFF Research Database (Denmark)

    Chaudhary, Sanjay Kumar; Teodorescu, Remus; Rodriguez, Pedro;

    2009-01-01

    This paper describes the modelling and simulation of offshore wind power plants (WPP) connected to the onshore power system grid by VSC based HVDC transmission. Offshore wind power plant is modelled with several wind turbine generators connected to two separate collector buses with their own plant...... step-up transformers. VSC's are modelled using ideal IGBT switches supplied by the gate pulses from their respective controllers. A sequence of operation has been simulated from the starting up of the VSC-HVDC transmission, energizing the offshore grid and subsequent synchronization of the individual...... wind turbines. Simulation of power ramping up and down as well as steady state operation has been demonstrated. As an additional case, the primary reserve control logic has been implemented and simulated in PSCAD model....

  6. Power Flow Analysis of HVAC and HVDC Transmission Systems for Offshore WindParks

    DEFF Research Database (Denmark)

    da Silva, Filipe Miguel Faria; Castro, Rui

    2009-01-01

    , the two options are analysed from a power flow point of view. The influence in the voltage regulation of the onshore connection busbar is investigated in a 57 bus test power system. The simulation results obtained for each one of the above mentioned transmission system configurations allow the conclusion......As the onshore wind resource is running shorter, wind power promoters are paying attention to the offshore resources. As in most cases there is no load offshore, wind power must be transmitted to the main land. To do so, two options are available: HVAC and HVDC transmission systems. In this paper...... that HVAC solution is limited by the distance to shore and by the wind transmitted power. HVDC options do not show these limitations, but are more expensive and more delicate to deal with, because there is a lack of operational experience, so far....

  7. Design of protective inductors for HVDC transmission line within DC grid offshore wind farms

    DEFF Research Database (Denmark)

    Deng, Fujin; Chen, Zhe

    2013-01-01

    This paper presents fault analysis and protective inductors design for an offshore wind farm, where the power collection system in the wind farm and the power transmission link to the grid adopt high-voltage direct-current (HVDC) technology. This paper focuses on dealing with short-circuit faults...... in the HVDC link between the offshore station and the onshore station. The transient characteristics of the transmission system are analyzed in detail. The criteria of selecting protective inductors are proposed to effectively limit the short-circuit current and avoid the damage to the converters. A dc grid...... offshore wind farm is simulated, and the results demonstrate the effectiveness of the proposed protective inductors design....

  8. Coordinated system services from offshore wind power plants connected through HVDC networks

    DEFF Research Database (Denmark)

    Zeni, L.; Glasdam, Jakob Bærholm; Hesselbæk, B.

    2014-01-01

    This paper presents an overview of power system services in networks involving multiple onshore power systems, a voltage sourced converter (VSC) based high voltage direct current (HVDC) offshore network and an offshore wind power plant (OWPP). A comprehensive list of services regarding onshore...... control and communication delays of OWPPs, and their influence on the successful delivery of the targeted services. Furthermore, it is shown that as an HVDC network increases in size from the point-to-point, the handling of onshore short circuits calls for the proper combination of DC chopper(s) and fast...... as well as offshore network operation – both AC and DC – will be discussed from a state of the art perspective. Among them, the most interesting have been selected and will be treated in more detail and the main contribution of this paper will be to shed light on the most relevant aspects related...

  9. Like Father, Like Son? A Comparison of the Foreign Policies of George H.W. Bush and George W. Bush

    Directory of Open Access Journals (Sweden)

    Marc J. O'Reilly

    2009-12-01

    Full Text Available Este artículo aplica aproximaciones cognitivas (por ejemplo, la del liderazgo y poliheurísticas a la toma de decisiones en política exterior para explicar las variaciones en las políticas de George H. W. Bush y George W. Bush. Yuxtaponer estos enfoques relacionados ilustra el cómo y el por qué del proceso  de toma de decisiones de los presidentes estadounidenses, proporcionando un sintético pero más trabajado, análisis en la comprensión de la política exterior, especialmente cuando ésta afecta a las presidencias. La sección inicial del artículo confronta las dos teorías. La siguiente sección examina decisiones importantes a través de estudios de caso (uno por cada administración. La sección final analiza las decisiones dentro del contexto teórico. Mientras que el artículo enfatiza el nivel individual de análisis, factores tanto estructurales como doméstico también serán tenidos en cuenta._______________________ABSTRACT:This article applies cognitive (i.e., leadership and poliheuristic approaches to foreign-policy decision making to explain variances in the policies of George H.W. Bush and George W. Bush. Juxtaposing these related approaches highlights the how and why of presidential decision making, providing a synthetic, though more cogent, understanding of foreign-policy analysis -- especially as it pertains to presidencies. The initial section of the article discusses the two theories. The following section examines important decisions via case studies – one for each administration. The final section analyzes the decisions in the context of the theories. While this article emphasizes the individual level of analysis, structural as well as domestic factors will also be discussed.

  10. George Bush peab sõjalist jõudu viimaseks valikuks / George W. Bush ; interv. Kaarel Kaas

    Index Scriptorium Estoniae

    Bush, George W., 1946-

    2005-01-01

    Ilmunud ka: Põhjarannik 7. mai 2005, lk. 2, Severnoje Poberezhje 7. mai, 2005, lk. 2. USA president George Bush andis 5. mail Valges Majas intervjuu kuuele Euroopa ajakirjanikule. 9. mai pidustustest Moskvas, USA-Läti, Venemaa-Balti riikide suhetest, demokraatiast Venemaal, Ameerika Ühendriikide ning Baltimaade viisarežiimist, vabaduse mõistestst, kinnipeetavate kohtlemisest Guantanamo sõjaväebaasis, relvade kasutamise vajadusest, terrorismist. Vt. samas: Kuidas usutlus võimalikuks sai

  11. George Bush peab sõjalist jõudu viimaseks valikuks / George W. Bush ; interv. Kaarel Kaas

    Index Scriptorium Estoniae

    Bush, George W., 1946-

    2005-01-01

    Ilmunud ka: Põhjarannik 7. mai 2005, lk. 2, Severnoje Poberezhje 7. mai, 2005, lk. 2. USA president George Bush andis 5. mail Valges Majas intervjuu kuuele Euroopa ajakirjanikule. 9. mai pidustustest Moskvas, USA-Läti, Venemaa-Balti riikide suhetest, demokraatiast Venemaal, Ameerika Ühendriikide ning Baltimaade viisarežiimist, vabaduse mõistestst, kinnipeetavate kohtlemisest Guantanamo sõjaväebaasis, relvade kasutamise vajadusest, terrorismist. Vt. samas: Kuidas usutlus võimalikuks sai

  12. A Solid-State Fault Current Limiting Device for VSC-HVDC Systems

    Science.gov (United States)

    Larruskain, D. Marene; Zamora, Inmaculada; Abarrategui, , Oihane; Iturregi, Araitz

    2013-08-01

    Faults in the DC circuit constitute one of the main limitations of voltage source converter VSC-HVDC systems, as the high fault currents can damage seriously the converters. In this article, a new design for a fault current limiter (FCL) is proposed, which is capable of limiting the fault current as well as interrupting it, isolating the DC grid. The operation of the proposed FCL is analysed and verified with the most usual faults that can occur in overhead lines.

  13. 自激式SVC在HVDC中的应用%Auto-Excitation Type SVC Applied in HVDC

    Institute of Scientific and Technical Information of China (English)

    陈玉安; 李燕平

    2002-01-01

    @@ 1问题的提出 直流输电(HVDC)以其易于联网、系统稳定、宜大功率远距离输电一系列优点正被世界各国所采用.目前,HVDC的换流装置所使用的是换相关断型晶闸管构成的它激式换流器.

  14. Simulation Model of the Future Nordic Power Grid Considering the Impact of HVDC Links

    OpenAIRE

    Aas, Even Strand

    2016-01-01

    As Europe is shifting to an increasingly larger share of non-dispatchable renewable energy sources, the cross-border power flow changes. This thesis considers further development of an existing PowerFactory simulation model designed to fit with new power flow situations influencing the Nordic power system. Today, there are many HVDC links connecting Europe to the Nordic grid, and there are several new links being built and planned. The thesis work is a continuation of an earlier specialisatio...

  15. Multilevel Modular Converter for VSC-HVDC Transmission Applications: Control and Operational Aspects

    DEFF Research Database (Denmark)

    Gnanarathna, Udana N.; Gole, Aniruddha M.; Chaudhary, Sanjay Kumar

    2010-01-01

    Control methods for a new class of converter, the multilevel modular converter (MMC), recently introduced for HVDC transmission are discussed. The paper discusses converter-level controls including firing pulse generation and capacitor voltage balancing. It also covers higher level controls...... for incorporating the converter into a larger power network, with a weak ac receiving end. The performance behavior is studied using electromagnetic transients simulation....

  16. HVDC-System-Interaction Assessment through Line-Flow Change-Distribution Factor and Transient-Stability Analysis at Planning Stage

    Directory of Open Access Journals (Sweden)

    Sungchul Hwang

    2016-12-01

    Full Text Available Many of the recent projects for new transmission line have considered the high-voltage direct current (HVDC system, owing to the many advantages of the direct current (DC system. The most noteworthy advantage is that a cable can serve as a substitute for the overhead transmission line in residential areas; therefore, the HVDC system application is increasing, and as the number of DC systems in the power system increases, the interaction assessment regarding the HVDC system gains importance. An index named multi-infeed interaction factor (MIIF is commonly used to estimate the interaction between power converters; however, the HVDC system is composed of two converters and a transmission line. The MIIF represents the interaction between the rectifiers and inverters, but not for the whole system. In this work, a method to assess the interaction of the whole system was therefore studied. To decide on the location of the new HVDC transmission system at the planning stage, in consideration of the interaction of the existing DC system, the line flow change distribution factor, according to the HVDC-transmission capacity change, was examined. Also, a power system transient -stability analysis was performed with different HVDC system locations, depending on the distribution factor. The simulation results indicate that when the factor is higher, two HVDC systems have a stronger interaction and are less stable in the transient state.

  17. Reprint of “Performance analysis of a model-sized superconducting DC transmission system based VSC-HVDC transmission technologies using RTDS”

    Science.gov (United States)

    Dinh, Minh-Chau; Ju, Chang-Hyeon; Kim, Sung-Kyu; Kim, Jin-Geun; Park, Minwon; Yu, In-Keun

    2013-01-01

    The combination of a high temperature superconducting DC power cable and a voltage source converter based HVDC (VSC-HVDC) creates a new option for transmitting power with multiple collection and distribution points for long distance and bulk power transmissions. It offers some greater advantages compared with HVAC or conventional HVDC transmission systems, and it is well suited for the grid integration of renewable energy sources in existing distribution or transmission systems. For this reason, a superconducting DC transmission system based HVDC transmission technologies is planned to be set up in the Jeju power system, Korea. Before applying this system to a real power system on Jeju Island, system analysis should be performed through a real time test. In this paper, a model-sized superconducting VSC-HVDC system, which consists of a small model-sized VSC-HVDC connected to a 2 m YBCO HTS DC model cable, is implemented. The authors have performed the real-time simulation method that incorporates the model-sized superconducting VSC-HVDC system into the simulated Jeju power system using Real Time Digital Simulator (RTDS). The performance analysis of the superconducting VSC-HVDC systems has been verified by the proposed test platform and the results were discussed in detail.

  18. Modelisation et simulation d'une liaison HVDC de type VSC-MMC

    Science.gov (United States)

    Saad, Hani Aziz

    High-voltage direct current transmission systems (HVDC) are rapidly expanding in the world. Two main factors are responsible for this expansion. The first is related to the difficulty of building new overhead lines to ensure the development of high-voltage AC grids, which makes the usage of underground cables more common. However, the use of such cables is limited in length to a few tens of km because of the capacitive current generated by the cable itself. Beyond this length limit, the solution is usually to transmit in DC. The second factor is related to the development of offshore wind power plants that require connecting powers of several hundred of MW to the mainland grid by cables whose lengths can reach several hundreds of km and consequently require HVDC transmission system. Several HVDC projects are currently planned and developed by the French transmission system operator RTE. One of such projects is the INELFE interconnection project, with a capacity of 2,000 MW, between France and Spain. This thesis has been funded by RTE, in order to model and simulate in off-line and real time modes, modern HVDC interconnections. The delivered simulation means are used to examine targeted HVDC system performances and risks of abnormal interactions with surrounding power systems. The particularity of the INELFE HVDC system is the usage of a dedicated control system that will largely determine the dynamic behaviour of the system for both large disturbances (faults on the network) and small perturbations (power step changes). Various VSC topologies, including the conventional two-level, multi-level diode-clamped and floating capacitor multi-level converters, have been proposed and reported in the literature. However, due to the complexity of controls and practical limitations, the VSC-HVDC system installations have been limited to the two-level and three-level diode-clamped converters. Recently, the development of modular technology called MMC (Modular Multilevel

  19. Restoration of Normal Frequency Affected by Small Load Variations Through HVDC link Using Neuro-Fuzzy Approach

    Directory of Open Access Journals (Sweden)

    Anil Kumar Sharma,

    2011-03-01

    Full Text Available HVDC power transmission is coming up with merits to replace the EHV-AC system. The controller inverter operation can successfully regulate the power in HVDC link leading to fulfillment ofpower demand in A.C. networks caused by sudden rise in loading. Since overloading and unloading both lead to the departure of operating frequency below or above normal, its control for normalization isexercised through control of power flow in HVDC Link. Also the same is achieved by adjusting firing delay angle intelligently. This paper aims at providing automation to frequency normalization after it hasundergone changes from normal value of 50 Hz, due to sudden and sustained increase in load or due to working of generations at increased loads in H.V.D.C transmission systems. It is planned to automate the restoration of departed frequency to normal value by arranging the change in firing delay angle i.e. α of the converter of H.V.D.C. link till the increased load demand is met with. An adaptive control system has been devised which controls the firing delay angle on the basis of decisions given by a fuzzy controller. Also the fuzzy controls are decided by the departure in frequency from normal. The results have been found to be encouraging.

  20. Vibration and Audible Noise of Filter Capacitors in HVDC Converter Stations%Vibration and Audible Noise of Filter Capacitors in HVDC Converter Stations

    Institute of Scientific and Technical Information of China (English)

    ZHU Ling-yu; JI Sheng-chang

    2011-01-01

    The filter capacitor stack is one of the main acoustic noise sources in high-voltage DC (HVDC) converter stations. As HVDC systems are built more and more recently, it is significant to research the audible noise of filter capacitors. In this paper, the current situation of research on vibration and audible noise of filter capacitors in HVDC converter stations, which is departed into three parts--generation mechanism, prediction methods, and reduction measures, is presented and the research achievements are discussed. Scholars have built the model that the alternating electric force caused by the voltage conduces to the vibration, which propagates to the enclosure and radiates audible noise. As a result, the parts contributing most to the generation of audible noise are the top and the bottom of capacitors. In the noise level prediction respect, several methods have been prospected including impact hammer, sweep frequency, impact current, monopole and Kirchhoff formula method, which are suitable for single capacitors or capacitors stacks individually. However, the sweep frequency method is restricted by experiment condition, and the impact current method needs further research and verified. On the other hand, CIGRE WG14.26 provides three sound reduction measures, but all of them are not so practicable, while MPP absorber and compressible space absorber prospected by Dr. Wu Peng are proved to be effective. The sound barriers are also considered by scholars, and the acoustic directivity performance of capacitors is also researched. Besides, the developing direction of each research field is prospected in corresponding part.

  1. 风电场向孤岛输电的VSC-HVDC Light的建模与仿真%Modelling and Simulation of VSC-HVDC Light for Electricity Transmission from Wind Farm to Solitary Island

    Institute of Scientific and Technical Information of China (English)

    谢海良; 王爱花; 赵君亮

    2014-01-01

    We introduced the operating principle and system of HVDC Light,which is based on the controlling of VSC. The simulation model of VSC-HVDC Light for electricity transmission from wind farm to solitary island by MATLAB is founded and simulated. The simulation result showed that system DC voltage value corresponds with the set value. The both ends of voltage value achieve coordination. Coordination control and self-banlancing transmission of active power are actualized. All quantities of states meet the theoretical value. The model accurately simulates the steady working condition of VSC-HVDC Light system,and offers the scientific basis for practical engineering.%介绍了以VSC控制为基础的HVDC Light的系统结构和工作原理,在MATLAB中创建了风电场向孤岛输电的VSC-HVDC Light系统仿真模型,并对其进行了稳态仿真研究。对仿真结果进行分析可知,系统直流电压基本稳定在给定的电压值,两端直流电压实现了协调配合,有功功率实现了协调控制和自动平衡传输,各状态量都符合理论值,模型准确模拟出了VSC-HVDC Light系统的稳态工作状况,为实际工程提供了科学的理论依据。

  2. Taxonomy Icon Data: thick-tailed bush baby [Taxonomy Icon

    Lifescience Database Archive (English)

    Full Text Available thick-tailed bush baby Otolemur crassicaudatus Chordata/Vertebrata/Mammalia/Theria/Eutheria/Primate Otolemur..._crassicaudatus_L.png Otolemur_crassicaudatus_NL.png Otolemur_crassicaudatus_S.png Otolemur..._crassicaudatus_NS.png http://biosciencedbc.jp/taxonomy_icon/icon.cgi?i=Otolemur+crassicaudatus&t=L ...http://biosciencedbc.jp/taxonomy_icon/icon.cgi?i=Otolemur+crassicaudatus&t=NL htt...p://biosciencedbc.jp/taxonomy_icon/icon.cgi?i=Otolemur+crassicaudatus&t=S http://biosciencedbc.jp/taxonomy_icon/icon.cgi?i=Otolemur+crassicaudatus&t=NS ...

  3. Taxonomy Icon Data: Japanese Bush Warbler [Taxonomy Icon

    Lifescience Database Archive (English)

    Full Text Available Japanese Bush Warbler Cettia diphone Chordata/Vertebrata/Aves Cettia_diphone_L.png Cettia_diphone..._NL.png Cettia_diphone_S.png Cettia_diphone_NS.png http://biosciencedbc.jp/taxonomy_icon/icon.cgi?i=Cettia+diphone...&t=L http://biosciencedbc.jp/taxonomy_icon/icon.cgi?i=Cettia+diphone&t=NL http://bioscie...ncedbc.jp/taxonomy_icon/icon.cgi?i=Cettia+diphone&t=S http://biosciencedbc.jp/tax...onomy_icon/icon.cgi?i=Cettia+diphone&t=NS http://togodb.biosciencedbc.jp/togodb/view/taxonomy_icon_comment_en?species_id=26 ...

  4. A New Coordinated Voltage Control Scheme for Offshore AC Grid of HVDC Connected Offshore Wind Power Plants

    DEFF Research Database (Denmark)

    Sakamuri, Jayachandra N.; Cutululis, Nicolaos Antonio; Rather, Zakir Hussain;

    2015-01-01

    This paper proposes a coordinated voltage control scheme (CVCS) which enhances the voltage ride through (VRT) capability of an offshore AC grid comprised of a cluster of offshore wind power plants (WPP) connected through AC cables to the offshore voltage source converter based high voltage DC (VSC-HVDC......) converter station. Due to limited short circuit power contribution from power electronic interfaced variable speed wind generators and with the onshore main grid decoupled by the HVDC link, the offshore AC grid becomes more vulnerable to dynamic voltage events. Therefore, a short circuit fault...... in the offshore AC Grid is likely to have significant implications on the voltage of the offshore AC grid, hence on the power flow to the onshore mainland grid. The proposed CVCS integrates individual local reactive power control of wind turbines and of the HVDC converter with the secondary voltage controller...

  5. Research Status of HVDC XLPE Cable%高压直流XLPE电缆研究现状

    Institute of Scientific and Technical Information of China (English)

    王亚; 吕泽鹏; 吴锴; 王霞; 刘通; 李锐海

    2014-01-01

    The international application of high voltage direct current(HVDC) transmission cable was pre-sented. The research situation of space charge and test methods of the HVDC cable was summarized, and the development direction of the HVDC cable materials and test methods were prospected.%介绍了国际高压直流输电电缆绝缘的应用情况,概述了高压直流电缆的空间电荷与直流电缆测试方法的研究情况,展望了高压直流电缆材料及测试技术的发展方向。

  6. Field tests of Sub-Synchronous Oscillation damping and frequency controllers of the Rihand-Delhi HVDC bipole

    Energy Technology Data Exchange (ETDEWEB)

    Prasad, Mata [ABB, New Delhi (India); Rao, L.V.; Chakravorty, S.; Moni, R.S.; Dass, R. [National Thermal Power Corporation Ltd., New Delhi (India); Mishra, R.B.; Tripathi, D.B. [Powergrid (India); Bjorklund, Hans; Duchen, Hugo; Westling, Soren [ABB Power Systems, Ludvika (Sweden)

    1994-12-31

    The Rihand-Delhi Hvdc transmission system comprises of two poles in bipolar mode, each of 750 MW nominal capacity. The length of the transmission line is 814 km and the main objective of the link is the transmission of bulk power from the Singrauli/Rihand thermal generating complex to the major load centers near the National Capital region. As in all major Hvdc schemes, the Rihand-Delhi Hvdc project has also been provided with a SSO damping controller which was extensively tested in the simulator prior to installation. This paper describes some of the important field tests conducted to ascertain actual performance and compares the same with corresponding simulator cases. Also covered is the performance of the frequency controller. (author) 3 refs., 9 figs.

  7. Electromechanical Transient Modeling and Simulation for Voltage Source Converter Based HVDC Power Transmission%VSC-HVDC机电暂态仿真建模及仿真

    Institute of Scientific and Technical Information of China (English)

    刘昇; 徐政; 唐庚; 华文; 薛英林

    2013-01-01

    Based on the fundamental frequency mathematical model of VSC-HVDC power transmission in d-q rotating dq rotary coordinate system, the electromechanical transient mathematical equations of VSC-HVDC power transmission are summarized, afterwards a electromechanical transient model for VSC-HVDC power transmission is achieved based on user-defined function of PSS/E and the achieved model is compared with the precise electromagnetic transient model for VSC-HVDC power transmission in PSCAD, and simulation results show that the steady state power flows from the two models are very similar and their dynamic characteristics are highly consistent each other, thus the effectiveness and accuracy of the achieved electromechanical transient model for VSC-HVDC power transmission are verified. Finally, using the achieved model the application of VSC-HVDC power transmission in actual large-scale multi-infeed HVDC power transmission system is researched, and research results show that using VSC-HVDC power transmission technology the commutation failure occurred in traditional HVDC power transmission system can be radically resolved.%  以VSC-HVDC在dq旋转坐标系下的基频数学模型为基础,总结了 VSC-HVDC 的机电暂态数学方程。之后基于 PSS/E 自定义模型功能实现了 VSC-HVDC 机电暂态模型,并将该模型和PSCAD中VSC-HVDC电磁暂态精确模型进行了对比,仿真结果表明两者的稳态潮流十分接近,动态特性具有很好的一致性,从而验证了VSC-HVDC机电暂态模型的有效性和准确性。最后基于该模型对VSC-HVDC 在实际大规模多直流馈入系统中的应用进行了研究,结果表明 VSC-HVDC 从根本上解决了传统直流输电的换相失败问题。

  8. Suggested Methods for Preventing Core Saturation Instability in HVDC Transmission Systems

    Energy Technology Data Exchange (ETDEWEB)

    Norheim, Ian

    2002-07-01

    In this thesis a study of the HVDC related phenomenon core saturation instability and methods to prevent this phenomenon is performed. It is reason to believe that this phenomenon caused disconnection of the Skagerrak HVDC link 10 August 1993. Internationally, core saturation instability has been reported at several HVDC schemes and thorough complex studies of the phenomenon has been performed. This thesis gives a detailed description of the phenomenon and suggest some interesting methods to prevent the development of it. Core saturation instability and its consequences can be described in a simplified way as follows: It is now assumed that a fundamental harmonic component is present in the DC side current. Due to the coupling between the AC side and the DC side of the HVDC converter, a subsequent second harmonic positive-sequence current and DC currents will be generated on the AC side. The DC currents will cause saturation in the converter transformers. This will cause the magnetizing current to also have a second harmonic positive-sequence component. If a high second harmonic impedance is seen from the commutation bus, a high positive-sequence second harmonic component will be present in the commutation voltages. This will result in a relatively high fundamental frequency component in the DC side voltage. If the fundamental frequency impedance at the DC side is relatively low the fundamental component in the DC side current may become larger than it originally was. In addition the HVDC control system may contribute to the fundamental frequency component in the DC side voltage, and in this way cause a system even more sensitive to core saturation instability. The large magnetizing currents that eventually will flow on the AC side cause large zero-sequence currents in the neutral conductors of the AC transmission lines connected to the HVDC link. This may result in disconnection of the lines. Alternatively, the harmonics in the large magnetizing currents may cause

  9. Suggested Methods for Preventing Core Saturation Instability in HVDC Transmission Systems

    Energy Technology Data Exchange (ETDEWEB)

    Norheim, Ian

    2002-07-01

    In this thesis a study of the HVDC related phenomenon core saturation instability and methods to prevent this phenomenon is performed. It is reason to believe that this phenomenon caused disconnection of the Skagerrak HVDC link 10 August 1993. Internationally, core saturation instability has been reported at several HVDC schemes and thorough complex studies of the phenomenon has been performed. This thesis gives a detailed description of the phenomenon and suggest some interesting methods to prevent the development of it. Core saturation instability and its consequences can be described in a simplified way as follows: It is now assumed that a fundamental harmonic component is present in the DC side current. Due to the coupling between the AC side and the DC side of the HVDC converter, a subsequent second harmonic positive-sequence current and DC currents will be generated on the AC side. The DC currents will cause saturation in the converter transformers. This will cause the magnetizing current to also have a second harmonic positive-sequence component. If a high second harmonic impedance is seen from the commutation bus, a high positive-sequence second harmonic component will be present in the commutation voltages. This will result in a relatively high fundamental frequency component in the DC side voltage. If the fundamental frequency impedance at the DC side is relatively low the fundamental component in the DC side current may become larger than it originally was. In addition the HVDC control system may contribute to the fundamental frequency component in the DC side voltage, and in this way cause a system even more sensitive to core saturation instability. The large magnetizing currents that eventually will flow on the AC side cause large zero-sequence currents in the neutral conductors of the AC transmission lines connected to the HVDC link. This may result in disconnection of the lines. Alternatively, the harmonics in the large magnetizing currents may cause

  10. President Bush's Pre-War Rhetoric on Iraq: Paranoid Style in Action

    Science.gov (United States)

    Nikolaev, Alexander G.; Porpora, Douglas V.

    2006-01-01

    The focus of this article is on the war rhetoric of the Bush administration as reflected in the speeches of President Bush. What was explored is how presidential speeches drew on a variety of rhetorical techniques, from role-taking and punctuation to the adoption of the paranoid style. The purpose of these techniques is to nullify voices of…

  11. Assessing the Debt: George W. Bush's Legacy and the Future of Public Education under Barack Obama

    Science.gov (United States)

    Means, Alex; Taylor, Kendall

    2010-01-01

    This article utilizes Gloria Ladson-Billings' notion of educational debt in order to explore the historical, economic, and cultural politics of education reform under George W. Bush and Barack Obama. It tracks the No Child Left Behind Act across a number of fields in order to claim that Bush's expansion of the educational debt should be understood…

  12. Does phenology distinguish bitter and sweet African bush mango trees (Irvingia spp., Irvingiaceae)?

    NARCIS (Netherlands)

    Vihotogbe, R.; Berg, van den R.G.; Bongers, F.; Sinsin, B.; Sosef, M.S.M.

    2014-01-01

    Key message This phenological analysis of bitter and sweet bush mango trees is part of their biosystematics. It supports the species distinction hypothesis postulated by Harris (Bull J Bot Nat Belg 65(1-2):143-196, 1996 ) and Lowe et al. (Mol Ecol 9:831-841, 2000 ). African Bush Mango trees are

  13. Does phenology distinguish bitter and sweet African bush mango trees (Irvingia spp., Irvingiaceae)?

    NARCIS (Netherlands)

    Vihotogbe, R.; Berg, van den R.G.; Bongers, F.; Sinsin, B.; Sosef, M.S.M.

    2014-01-01

    Key message This phenological analysis of bitter and sweet bush mango trees is part of their biosystematics. It supports the species distinction hypothesis postulated by Harris (Bull J Bot Nat Belg 65(1-2):143-196, 1996 ) and Lowe et al. (Mol Ecol 9:831-841, 2000 ). African Bush Mango trees are prio

  14. Fatigue Analysis of an Outer Bearing Bush of a Kaplan Turbine

    Directory of Open Access Journals (Sweden)

    Doina Frunzaverde

    2011-01-01

    Full Text Available The paper presents the fatigue analysis of an outer bearing bush of aKaplan turbine. This outer bush, together with an inner one, bear thepin lever - trunion - blade subassembly of the runner blade operatingmechanism. For modeling and simulation, SolidWorks software is used.

  15. Morphological Characterization of African Bush Mango trees (Irvingia species) in the Dahomey Gap (West Africa)

    NARCIS (Netherlands)

    Vihotogbe, R.; Berg, van den R.G.; Sosef, M.S.M.

    2013-01-01

    The variation of the morphological characters of bitter and sweet African bush mango trees (Irvingia species) was investigated in the Dahomey Gap which is the West African savannah woodland area separating the Upper and the Lower Guinean rain forest blocks. African bush mangoes have been rated as th

  16. Renewable Energy in Eastern North Africa in Terms of Patterns of Coupling to Czisch European HVDC Super Grid

    Directory of Open Access Journals (Sweden)

    K Boubaker

    2013-06-01

    Full Text Available In this study, wind energy potential and perspectives in the eastern North Africa region (Tunisia have been investigated in terms of connectivity to the projected Czisch European HVDC super grid. A simplified extracted scheme of this grid has been used as a guide to optimize transportation efficiency through the whole net. Wind, as an available and easily exploitable renewable energy was showing to have a promising future for 2025 horizon in the context of a connected net with the European Union, despite local sub-grids disparities. This is also to emphasis HVDC technology adequacy for economical power transmission over very long distances andconnection between differently established grids.

  17. Second Order Cone Programming (SOCP) Relaxation Based Optimal Power Flow with Hybrid VSC-HVDC Transmission and Active Distribution Networks

    DEFF Research Database (Denmark)

    Ding, Tao; Li, Cheng; Yang, Yongheng

    2017-01-01

    The detailed topology of renewable resource bases may have the impact on the optimal power flow of the VSC-HVDC transmission network. To address this issue, this paper develops an optimal power flow with the hybrid VSC-HVDC transmission and active distribution networks to optimally schedule...... the generation output and voltage regulation of both networks, which leads to a non-convex programming model. Furthermore, the non-convex power flow equations are based on the Second Order Cone Programming (SOCP) relaxation approach. Thus, the proposed model can be relaxed to a SOCP that can be tractably solved...

  18. Indigenous Methods in Preserving Bush Mango Kernels in Cameroon

    Directory of Open Access Journals (Sweden)

    Zac Tchoundjeu

    2005-01-01

    Full Text Available Traditional practices for preserving Irvingia wombolu and Irvingia gabonensis (bush mango kernels were assessed in a survey covering twelve villages (Dongo, Bouno, Gribi [East], Elig-Nkouma, Nkom I, Ngoumou [Centre], Bidjap, Nko’ovos, Ondodo [South], Besong-Abang, Ossing and Kembong [Southwest], in the humid lowland forest zone of Cameroon. All the interviewed households that own trees of species were found to preserve kernels in periods of abundance, excluding Elig-Nkouma (87.5%. Eighty nine and 85% did so in periods of scarcity for I. wombolu and I. gabonensis respectively. Seventeen and twenty-nine kernel preservation practices were recorded for I. wombolu and I. gabonensis respectively. Most were based on continuous heating of the kernels or kernel by-products (cakes. The most commonly involved keeping the sun-dried kernels in a plastic bag on a bamboo rack hung above the fireplace in the kitchen. A 78% of interviews households reported preserving I. wombolu kernels for less than one year while 22% preserved it for more than one year with 1.9% for two years, the normal length of the off-season period for trees in the wild. Cakes wrapped with leaves and kept on a bamboo rack hung over the fireplace were reported by households in the East and South provinces to store Irvingia gabonensis longer (more than one year. Further studies on the utilization of heat for preserving and canning bush mango kernels are recommended.

  19. Environmental geophysics, offshore Bush River Peninsula, Aberdeen Proving Ground, Maryland

    Energy Technology Data Exchange (ETDEWEB)

    Miller, S.F.; Kuecher, G.J.; Davies, B.E. [and others

    1995-11-01

    Geophysical studies in shallow waters adjacent to the Bush River Peninsula, Edgewood Area of Aberdeen Proving Ground, Maryland, have delineated the extent of waste disposal sites and established a hydrogeologic framework, which may control contaminant transport offshore. These studies indicate that during the Pleistocene Epoch, alternating stands of high and low sea levels resulted in a complex pattern of shallow channel-fill deposits around the Bush River Peninsula. Ground-penetrating radar studies reveal paleochannels greater than 50 ft deep. Some of the paleochannels are also imaged with marine seismic reflection. Conductivity highs measured with the EM-31 are also indicative of paleochannels. This paleochannel depositional system is environmentally significant because it may control the shallow groundwater flow regime beneath the peninsula. Magnetic, conductivity, and side-scan sonar anomalies outline anthropogenic anomalies in the study area. On the basis of geophysical data, underwater anthropogenic materials do exist in some isolated areas, but large-scale offshore dumping has not occurred in the area studied.

  20. Vibration monitoring via nano-composite piezoelectric foam bushings

    Science.gov (United States)

    Bird, Evan T.; Merrell, A. Jake; Anderson, Brady K.; Newton, Cory N.; Rosquist, Parker G.; Fullwood, David T.; Bowden, Anton E.; Seeley, Matthew K.

    2016-11-01

    Most mechanical systems produce vibrations as an inherent side effect of operation. Though some vibrations are acceptable in operation, others can cause damage or signal a machine’s imminent failure. These vibrations would optimally be monitored in real-time, without human supervision to prevent failure and excessive wear in machinery. This paper explores a new alternative to currently-used machine-monitoring equipment, namely a piezoelectric foam sensor system. These sensors are made of a silicone-based foam embedded with nano- and micro-scale conductive particles. Upon impact, they emit an electric response that is directly correlated with impact energy, with no electrical power input. In the present work, we investigated their utility as self-sensing bushings on machinery. These sensors were found to accurately detect both the amplitude and frequency of typical machine vibrations. The bushings could potentially save time and money over other vibration sensing mechanisms, while simultaneously providing a potential control input that could be utilized for correcting vibrational imbalance.

  1. Electrical insulation design and evaluation of 60 kV prototype condenser cone bushing for the superconducting equipment

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Woo-Ju, E-mail: shinwooju@hanyang.ac.kr; Lee, Jong-Geon; Hwang, Jae-Sang; Seong, Jae-Kyu; Lee, Bang-Wook, E-mail: bangwook@hanyang.ac.kr

    2013-11-15

    Highlights: •The optimum design of condenser cone cryogenic bushing was investigated. •Multi-layer aluminum foils in the bushing insulation body was designed and analyzed. •The optimum electric field distribution was selected by simulation. •The 60 kV FRP condenser cone cryogenic bushing was fabricated and tested. •BIL test corresponding to IEC 60137 was successfully performed for the bushing. -- Abstract: A cryogenic bushing is an essential component to be developed for commercial applications of high voltage (HV) superconducting devices. Due to the steep temperature gradient of the ambient of cryogenic bushing, general gas bushing adopting SF6 gas as an insulating media could not be directly used due to the freezing of SF6 gas. Therefore, condenser type bushing with special material considering cryogenic environment would be better choice for superconducting equipment. Considering these circumstance, we focused on the design of condenser bushing made of fiber reinforced plastic (FRP). In case of the design of the condenser bushing, it is very important to reduce the electric field intensification on the mounted flange part of the cryostat, which is the most vulnerable part of bushings. In this paper, design factors of cryogenic bushing were analyzed, and finally 60 kV condenser bushing was fabricated and tested. In order to achieve optimal electric field configuration, the configuration of condenser cone was determined using 2D electric field simulation results. Based on the experimental and the analytical works, 60 kV FRP condenser bushing was fabricated. Finally, the fabricated condenser bushing has been tested by applying lightning impulse and AC overvoltage test. From the test results, it was possible to get satisfactory results which confirm the design of cryogenic bushing in cryogenic environment.

  2. Characteristics and Application of VSC-HVDC Transmission System%VSC-HVDC输电系统的特点与应用

    Institute of Scientific and Technical Information of China (English)

    唐博; 王鹏

    2014-01-01

    轻型直流输电系统是基于VSC技术的新型直流输电技术。介绍轻型直流输电基本原理,对比轻型直流输电技术与传统直流输电技术在结构和功能方面的区别,阐述轻型直流输电的优点,并对其应用进行总结和展望,以期为轻型直流输电技术在我国的应用和发展提供一定参考。%With the development of semiconductors and renewable generation, a new HVDC technology-HVDC Light based on VSC (Voltage Sourced Converters) arises. The principle of HVDC Light technology is presented in this paper and then a comparison of config-uration as well as function is made between HVDC Light and conventional HVDC, and the merits of HVDC Light are clarified. At last, the application of HVDC Light is summarized and prospected.

  3. Bush Encroachment Mapping for Africa - Multi-Scale Analysis with Remote Sensing and GIS

    Science.gov (United States)

    Graw, V. A. M.; Oldenburg, C.; Dubovyk, O.

    2015-12-01

    Bush encroachment describes a global problem which is especially facing the savanna ecosystem in Africa. Livestock is directly affected by decreasing grasslands and inedible invasive species which defines the process of bush encroachment. For many small scale farmers in developing countries livestock represents a type of insurance in times of crop failure or drought. Among that bush encroachment is also a problem for crop production. Studies on the mapping of bush encroachment so far focus on small scales using high-resolution data and rarely provide information beyond the national level. Therefore a process chain was developed using a multi-scale approach to detect bush encroachment for whole Africa. The bush encroachment map is calibrated with ground truth data provided by experts in Southern, Eastern and Western Africa. By up-scaling location specific information on different levels of remote sensing imagery - 30m with Landsat images and 250m with MODIS data - a map is created showing potential and actual areas of bush encroachment on the African continent and thereby provides an innovative approach to map bush encroachment on the regional scale. A classification approach links location data based on GPS information from experts to the respective pixel in the remote sensing imagery. Supervised classification is used while actual bush encroachment information represents the training samples for the up-scaling. The classification technique is based on Random Forests and regression trees, a machine learning classification approach. Working on multiple scales and with the help of field data an innovative approach can be presented showing areas affected by bush encroachment on the African continent. This information can help to prevent further grassland decrease and identify those regions where land management strategies are of high importance to sustain livestock keeping and thereby also secure livelihoods in rural areas.

  4. Are Our President Learning? Unpacking the Enthymematic Connections in the Speech Mistakes of President George W. Bush

    Science.gov (United States)

    Quinlan, Margaret M.; Bates, Benjamin R.

    2010-01-01

    The purpose of this paper is to explore public interpretations of President George W. Bush's speaking errors. One interpretation of Bush's speech mistakes offered in the media is that he may have dyslexia. Therefore, we explore how an enthymeme using markers of dyslexia as a sign of bad leadership has been used to frame Bush's speaking errors. We…

  5. Variable Frequency Operations of an Offshore Wind Power Plant with HVDC-VSC: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Gevorgian, V.; Singh, M.; Muljadi, E.

    2011-12-01

    In this paper, a constant Volt/Hz operation applied to the Type 1 wind turbine generator. Various control aspects of Type 1 generators at the plant level and at the turbine level will be investigated. Based on DOE study, wind power generation may reach 330 GW by 2030 at the level of penetration of 20% of the total energy production. From this amount of wind power, 54 GW of wind power will be generated at offshore wind power plants. The deployment of offshore wind power plants requires power transmission from the plant to the load center inland. Since this power transmission requires submarine cable, there is a need to use High-Voltage Direct Current (HVDC) transmission. Otherwise, if the power is transmitted via alternating current, the reactive power generated by the cable capacitance may cause an excessive over voltage in the middle of the transmission distance which requires unnecessary oversized cable voltage breakdown capability. The use of HVDC is usually required for transmission distance longer than 50 kilometers of submarine cables to be economical. The use of HVDC brings another advantage; it is capable of operating at variable frequency. The inland substation will be operated to 60 Hz synched with the grid, the offshore substation can be operated at variable frequency, thus allowing the wind power plant to be operated at constant Volt/Hz. In this paper, a constant Volt/Hz operation applied to the Type 1 wind turbine generator. Various control aspects of Type 1 generators at the plant level and at the turbine level will be investigated.

  6. Fault ride-through and grid support of permanent magnet synchronous generator-based wind farms with HVAC and VSC-HVDC transmission systems

    DEFF Research Database (Denmark)

    Liu, Hongzhi; Chen, Zhe

    2012-01-01

    This paper describes fault ride-through and grid support of offshore wind farms based on permanent magnet synchronous generator (PMSG) wind turbines connected to the onshore AC network through two alternative transmission systems: high voltage AC (HVAC) or high voltage DC (HVDC) based on voltage...... source converters (VSC). The proposed configurations of the PMSG-based offshore wind farm and VSC-based HVDC are given as well as their control strategies under both steady state and fault state. The PMSG-based offshore wind farm is integrated into a test power transmission system via either HVAC or VSC-HVDC...

  7. Analysis on Electric Field Around HVAC-HVDC Hybrid Transmission Lines%Analysis on Electric Field Around HVAC-HVDC Hybrid Transmission Lines

    Institute of Scientific and Technical Information of China (English)

    LI Qian; LIU Jun-xiang; LI Hua; LIN Fu-chang

    2011-01-01

    As the transmission line corridors become more and more rare in China, it is now inevitable for people to construct HVAC-HVDC hybrid transmission lines. The research on the electric field around the transmission lines plays an important role in evaluating the electromagnetic environment nearby. However, few existing research now considered the mutual effect of HVAC-HVDC hybrid transmission lines. Thus, this research designed a program based on windows, which calculated the surface voltage gradient on the transmission lines and the electric field at ground level respectively. This research calculated the surface voltage gradient on the transmission lines by applying the improved method of successive images. For the electric field at ground level under AC transmission line, simula- tion charge method is used, while for the electric field at the ground level under DC transmission lines, deutsch as- sumption method is used. Comparing the results generated by the calculation with those in published literature, the program is reliable. Taking 500 kV transmission lines as an example, when considering the mutual effect of the HVAC-HVDC'lines, the amplitude of the surface voltage gradient will increase by about 10% and the amplitude of the electric field at ground level will increase by about 8%, making the mutual effect of the AC and DC lines unneglectable. Larger part of the electric field at ground level under hybrid lines is produced by the DC line. Thus, in order to control the electric field at ground level under hybrid lines, it should pay more attention on that produced by the DC line.

  8. Inertial Response of an Offshore Wind Power Plant with HVDC-VSC

    Energy Technology Data Exchange (ETDEWEB)

    Preciado, V.; Gevorgian, Vahan; Muljadi, Eduard; Madrigal, M.

    2017-01-05

    This paper analyzes the inertial response of an offshore wind power plant (WPP) to provide ancillary services to the power system grid. The WPP is connected to a high-voltage direct-current voltage source converter HVDC-VSC to deliver the power to the onshore substation. The wind turbine generator (WTG) used is a doubly-fed induction generator (Type 3 WTG). In this paper we analyze a control method for the WTGs in an offshore WPP to support the grid and contribute ancillary services to the power system network. Detailed time domain simulations will be conducted to show the transient behavior of the inertial response of an offshore WPP.

  9. Rats avoid exposure to HVdc electric fields: a dose response study.

    Science.gov (United States)

    Creim, J A; Lovely, R H; Weigel, R J; Forsythe, W C; Anderson, L E

    1993-01-01

    Rats, given the choice, avoid exposure to alternating current (ac) 60-Hz electric fields at intensities > or = 75 kV/m. This study investigated the generality of this behavior by studying the response of rats when exposed to high voltage direct current (HVdc) electric fields. Three hundred eighty male Long Evans rats were studied in 9 experiments with 40 rats per experiment and in one experiment with 20 rats to determine 1) if rats avoid exposure to HVdc electric fields of varying field strengths, and 2) if avoidance did occur, what role, if any, the concentration of air ions would have on the avoidance behavior. In all experiments a three-compartment glass shuttlebox was used; either the left or right compartment could be exposed to a combination of HVdc electric fields and air ions while the other compartment remained sham-exposed. The third, center compartment was a transition zone between exposure and sham-exposure. In each experiment, the rats were individually assessed in 1-h sessions where half of the rats (n = 20) had the choice to locomote between the two sides being exposed or sham-exposed, while the other half of the rats (n = 20) were sham-exposed regardless of their location, except in one experiment where there was no sham-exposed group. The exposure levels for the first six experiments were 80, 55, 42.5, 30, -36, and -55 kV/m, respectively. The air ion concentration was constant at 1.4 x 10(6) ions/cc for the four positive exposure levels and -1.4 x 10(6) ions/cc for the two negative exposure levels. Rats having a choice between exposure and non-exposure relative to always sham-exposed control animals significantly reduced the amount of time spent on the exposed side at 80 kV/m (P HVdc exposure level was held constant at either -55 kV/m (for three experiments) or -55 kV/m (for 1 experiment) while the air ion concentration was varied between experiments at 2.5 x 10(5) ions/cc, 1.0 x 10(4) for two of the experiments and was below the measurement limit

  10. Numerical analysis of ionized fields associated with HVDC transmission lines including effect of wind

    Energy Technology Data Exchange (ETDEWEB)

    Li, X.

    1998-12-31

    The effects of corona discharge on the conductor surface of HVDC power transmission lines were studied. Corona discharges generate ion flow and can cause power losses and environmental concerns. Solving the problem of the ion flow field is difficult because of its nonlinearity and the effect of wind. The following two numerical algorithms were presented which address the problem associated with strong wind or bundled lines: (1) the finite element method (FEM) based optimization algorithm, and (2) the upwind FVM based relaxation algorithm. Both were successfully tested on a coaxial cylindrical configuration and on a unipolar line model in the presence of wind.

  11. Improvement of Power System Stability using Artificial Neural Network based HVDC Controls

    Directory of Open Access Journals (Sweden)

    Nagu Bhookya

    2013-06-01

    Full Text Available In this paper, investigation is carried out for the improvement of power system stability by utilizing auxiliary controls for controlling HVDC power flow. The current controller model and the line dynamics are considered in the stability analysis. Transient stability analysis is done on a multi-machine system, where, a neural network controller is developed to improve the stability of the power system and to improve the response time of the controller to the changing conditions in power system. The results show the application of the neural network controller in AC-DC power systems.

  12. HVDC Connected Offshore Wind Power Plants: Review and Outlook of Current Research

    DEFF Research Database (Denmark)

    Glasdam, Jakob; Zeni, Lorenzo; Gryning, Mikkel;

    2013-01-01

    This paper presents a state-of-the-art review on grid integration of large offshore wind power plants (OWPPs) using high voltage direct voltage (HVDC) for grid connection. The paper describes in detail selected challenges hereto and presents how DONG Energy Wind Power (DEWP) is addressing...... and the PED widely used in the wind turbine generators (WTGs). Challenges hereto include PED control system interaction (from a stability point of view), assessment of the quality of vendor supplied control systems and their robustness against e.g. short circuits and load rejection. Furthermore, the outcome...

  13. A Primary and Backup Protection Algorithm based on Voltage and Current Measurements for HVDC Grids

    OpenAIRE

    Abedrabbo, Mudar; Van Hertem, Dirk

    2016-01-01

    DC grids are susceptible to DC side faults, which lead to a rapid rise of the DC side currents. DC side faults should be detected in a very short time before fault currents cause damage to the system or equipment, e.g., exceed the maximum interruptible limits of DC circuit breaker. This paper presents a primary and backup protective data-based algorithm. The proposed algorithm depends on the local voltage and current measurements to detect and identify various kinds of faults in the HVDC grid...

  14. An Optoelectronic High-voltage Probe for Measuring Impulse Voltage Distribution of HVDC Converter Valve

    Institute of Scientific and Technical Information of China (English)

    方志; 邱毓昌

    2007-01-01

    A high-voltage optoelectronic probe is developed for measuring impulse voltage distribution along thyristor units in the HVDC converter valve. The dimension of the resistive voltage divider is optimized by means of numerical compttation of electric field. A pulse frequency modulation (PFM) mode is adopted for the data transmission link because of its immunity to high-intensity electromagnetic interference. Experimental results indicate that the linearity deviation for the whole measuring system is within ± 0.15 %, and therefore it can meet requirements specified by IEC60700-1.

  15. The first three 800 MW wind park grid connection projects with XLPE HVDC cables

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Dongping; Lebioda, Thomas Jan; Koochack-Zadeh, Masoumeh; Jung, Jochen [TenneT Offshore GmbH, Bayreuth (Germany). Asset Management Offshore

    2011-07-01

    This paper presents the first three wind grid connection projects in class of 800 MW by TenneT Offshore in the German North Sea. According to the requirements of transmission capacity, distance and other technical and environmental constraints, the HVDC-VSC-technology and XLPE-cable are chosen to fulfill the task of grid connection. To time of this publication, these three projects are in project implementation phase and under construction. In this paper the detailed information about those three projects will be introduced and the first experiences and challenges will be reviewed from the stand point of the coastal TSO. (orig.)

  16. Development of a remote bushing for actinide vitrification

    Energy Technology Data Exchange (ETDEWEB)

    Schumacher, R.F.; Ramsey, W.G.; Johnson, F.M. [and others

    1996-12-31

    The Savannah River Site (SRS) and the Savannah River Technology Center (SRTC) are combining their existing experience in handling highly radioactive, special nuclear materials with commercial glass fiberization technology in order to assemble a small vitrification system for radioactive actinide solutions. The vitrification system or {open_quotes}brushing{close_quotes}, is fabricated from platinum-rhodium alloy and is based on early marble remelt fiberization technology. Advantages of this unique system include its relatively small size, reliable operation, geometrical safety (nuclear criticality), and high temperature capability. The bushing design should be capable of vitrifying a number of the actinide nuclear materials, including solutions of americium/curium, neptunium, and possibly plutonium. State of the art, mathematical and oil model studies are being combined with basic engineering evaluations to verify and improve the thermal and mechanical design concepts.

  17. Comparison of PI and PR current controllers applied on two-level VSC-HVDC transmission system

    DEFF Research Database (Denmark)

    Manoloiu, A.; Pereria, H.A.; Teodorescu, Remus;

    2015-01-01

    This paper analyzes differences between αβ and dq reference frames regarding the control of two-level VSC-HVDC current loop and dc-link voltage outer loop. In the first part, voltage feedforward effect is considered with PI and PR controllers. In the second part, the feedforward effect is removed...

  18. An Examination of AC/HVDC Power Circuits for Interconnecting Bulk Wind Generation with the Electric Grid

    Directory of Open Access Journals (Sweden)

    Daniel Ludois

    2010-06-01

    Full Text Available The application of high voltage dc (HVDC transmission for integrating large scale and/or off-shore wind generation systems with the electric grid is attractive in comparison to extra high voltage (EHV ac transmission due to a variety of reasons. While the technology of classical current sourced converters (CSC using thyristors is well established for realization of large HVDC systems, the technology of voltage sourced converters (VSC is emerging to be an alternative approach, particularly suitable for multi-terminal interconnections. More recently, a more modular scheme that may be termed ‘bridge of bridge’ converters (BoBC has been introduced to realize HVDC systems. While all these three approaches are functionally capable of realizing HVDC systems, the converter power circuit design trade-offs between these alternatives are not readily apparent. This paper presents an examination of these topologies from the point of view of power semiconductor requirements, reactive component requirements, operating losses, fault tolerance, multi-terminal operation, modularity, complexity, etc. Detailed analytical models will be used along with a benchmark application to develop a comparative evaluation of the alternatives that maybe used by wind energy/bulk transmission developers for performing engineering trade-off studies.

  19. An examination of AC/HVDC power circuits for interconnecting bulk wind generation with the electric grid

    Energy Technology Data Exchange (ETDEWEB)

    Ludois, D.; Venkataramanan, G. [Department of Electrical and Computer Engineering, University of Wisconsin-Madison 1415 Engineering Dr. Madison WI 53706 (United States)

    2010-06-15

    The application of high voltage DC (HVDC) transmission for integrating large scale and/or off-shore wind generation systems with the electric grid is attractive in comparison to extra high voltage (EHV) AC transmission due to a variety of reasons. While the technology of classical current sourced converters (CSC) using thyristors is well established for realization of large HVDC systems, the technology of voltage sourced converters (VSC) is emerging to be an alternative approach, particularly suitable for multi-terminal interconnections. More recently, a more modular scheme that may be termed 'bridge of bridge' converters (BoBC) has been introduced to realize HVDC systems. While all these three approaches are functionally capable of realizing HVDC systems, the converter power circuit design trade-offs between these alternatives are not readily apparent. This paper presents an examination of these topologies from the point of view of power semiconductor requirements, reactive component requirements, operating losses, fault tolerance, multi-terminal operation, modularity, complexity, etc. Detailed analytical models will be used along with a benchmark application to develop a comparative evaluation of the alternatives that may be used by wind energy/bulk transmission developers for performing engineering trade-off studies. (author)

  20. Low-Cost Production of Composite Bushings for Jet Engine Applications

    Science.gov (United States)

    Gray, Robert A.

    1998-01-01

    The objectives of this research program were to reduce the manufacturing costs of variable stator vane bushings by 1) eliminating the expensive carbon fiber braiding operation, 2) replacing the batch mode impregnation, B-stage, and cutting operations with a continuous process, and 3) reducing the molding cycle and machining operations with injection molding to achieve near-net shapes. Braided bushings were successfully fabricated with both AMB-17XLD and AMB-TPD resin systems. The composite bushings achieved high glass transition temperature after post-cure (+300 C) and comparable weight loss to the PNM-15 bushings. ANM-17XLD bushings made with "batch-mode" molding compound (at 0.5 in. fiber length) achieved a +300 lb-force flange break strength which was superior to the continuous braided-fiber reinforced bushing. The non-MDA resin technology developed in this contract appears attractive for bushing applications that do not exceed a 300 C use temperature. Two thermoplastic polyimide resins were synthesized in order to generate injection molding compound powders. Excellent processing results were obtained at injection temperatures in excess of 300 C. Micro-tensile specimens were produced from each resin type and the Tg measurements (by TMA) for these samples were equivalent to AURUM(R). Thermal Gravimetric Analysis (TGA) conducted at 10 C/min showed that the non-MDA AMB-type polyimide thermoplastics had comparable weight loss to PMR-15 up to 500 C.

  1. Big data integration shows Australian bush-fire frequency is increasing significantly

    Science.gov (United States)

    Dutta, Ritaban; Das, Aruneema; Aryal, Jagannath

    2016-01-01

    Increasing Australian bush-fire frequencies over the last decade has indicated a major climatic change in coming future. Understanding such climatic change for Australian bush-fire is limited and there is an urgent need of scientific research, which is capable enough to contribute to Australian society. Frequency of bush-fire carries information on spatial, temporal and climatic aspects of bush-fire events and provides contextual information to model various climate data for accurately predicting future bush-fire hot spots. In this study, we develop an ensemble method based on a two-layered machine learning model to establish relationship between fire incidence and climatic data. In a 336 week data trial, we demonstrate that the model provides highly accurate bush-fire incidence hot-spot estimation (91% global accuracy) from the weekly climatic surfaces. Our analysis also indicates that Australian weekly bush-fire frequencies increased by 40% over the last 5 years, particularly during summer months, implicating a serious climatic shift. PMID:26998312

  2. Design and Range of Application of Slot Bushings with Volumetric Orifice Fields

    Institute of Scientific and Technical Information of China (English)

    ULYBYSHEV V. V.; VASEKIN V. V.; PERELMAN S. L.

    2012-01-01

    A design of a slot bushing with a volumetric field has been developed,which allows to produce continuous fibers from melts with difficult processing characteristics in order to produce fibers with better operating characteristics.The operability of the design was confirrned when solving two problems of special technological complexity.1.400- and 800-orifice bushings for production of continuous fibers from the basalt melt have been developed and recommended for manufacture.2.The process of production of continuous fibers from standard glass using 2400-orifice bushing with perforated plates instead of orifice tips without air cooling,has been realized for the first time.

  3. Artificial Neural Network and Rough Set for HV Bushings Condition Monitoring

    CERN Document Server

    Mpanza, LJ

    2011-01-01

    Most transformer failures are attributed to bushings failures. Hence it is necessary to monitor the condition of bushings. In this paper three methods are developed to monitor the condition of oil filled bushing. Multi-layer perceptron (MLP), Radial basis function (RBF) and Rough Set (RS) models are developed and combined through majority voting to form a committee. The MLP performs better that the RBF and the RS is terms of classification accuracy. The RBF is the fasted to train. The committee performs better than the individual models. The diversity of models is measured to evaluate their similarity when used in the committee.

  4. Ant Colony Optimization of Rough Set for HV Bushings Fault Detection

    CERN Document Server

    Mpanza, J L

    2011-01-01

    Most transformer failures are attributed to bushings failures. Hence it is necessary to monitor the condition of bushings. In this paper three methods are developed to monitor the condition of oil filled bushing. Multi-layer perceptron (MLP), Radial basis function (RBF) and Rough Set (RS) models are developed and combined through majority voting to form a committee. The MLP performs better that the RBF and the RS is terms of classification accuracy. The RBF is the fasted to train. The committee performs better than the individual models. The diversity of models is measured to evaluate their similarity when used in the committee.

  5. High-performance HVDC transmission over long distances; Hochleistungsuebertragung ueber grosse Entfernungen mit hochgespanntem Gleichstrom

    Energy Technology Data Exchange (ETDEWEB)

    Radtke, U. [PreussenElektra AG, Hannover (Germany)

    1998-12-31

    High-voltage DC transmission is a world-wide established technology for low-cost transmission of large amounts of electricity over long distances. Thanks to HVDC transmission, large amounts of electricity can now for the first time also be transmitted over long distances via ocean cable, something that cannot be done with AC power cables. HVDC transmission is independent of grid frequencies and can link grids of different frequency and different quality of frequency. Interconnected grids coupled via DC circuits can exploit additional technical and economic advantages such as mutual supply of power reserves, balancing of peak load, and modulation of active and reactive power. (orig.) [Deutsch] Die Hochspannungs-Gleichstromuebertragung (HGUe) ist eine weltweit etablierte Technik zur kostenguenstigen Uebertragung grosser elektrischer Leistungen ueber grosse Entfernungen. Sie schafft erstmals die Moeglichkeit, auch mittels Seekabel grosse Leistungen ueber Entfernungen zu uebertragen, die mit der Drehstromtechnik nicht moeglich sind. HGUeist unabhaengig von den Netzfrequenzen und kann Netze unterschiedlicher Frequenz und Frequenzguete miteinander verbinden. Ueber Gleichstromkreise gekuppelte Verbundnetze koennen zusaetzliche technische und wirtschaftliche Vorteile wie gegenseitige Bereitstellung von Kraftwerksreserven, Spitzenlastausgleich sowie Wirk- und Blindleistungsmodulation nutzt. (orig.)

  6. Relative Localization in Wireless Sensor Networks for Measurement of Electric Fields under HVDC Transmission Lines

    Directory of Open Access Journals (Sweden)

    Yong Cui

    2015-02-01

    Full Text Available In the wireless sensor networks (WSNs for electric field measurement system under the High-Voltage Direct Current (HVDC transmission lines, it is necessary to obtain the electric field distribution with multiple sensors. The location information of each sensor is essential to the correct analysis of measurement results. Compared with the existing approach which gathers the location information by manually labelling sensors during deployment, the automatic localization can reduce the workload and improve the measurement efficiency. A novel and practical range-free localization algorithm for the localization of one-dimensional linear topology wireless networks in the electric field measurement system is presented. The algorithm utilizes unknown nodes’ neighbor lists based on the Received Signal Strength Indicator (RSSI values to determine the relative locations of nodes. The algorithm is able to handle the exceptional situation of the output permutation which can effectively improve the accuracy of localization. The performance of this algorithm under real circumstances has been evaluated through several experiments with different numbers of nodes and different node deployments in the China State Grid HVDC test base. Results show that the proposed algorithm achieves an accuracy of over 96% under different conditions.

  7. La conception, la modelisation et la simulation du systeme VSC-HVDC offshore

    Science.gov (United States)

    Benhalima, Seghir

    Wind energy is recognized worldwide as a proven technology to meet the growing demands of green sustainable energy. To exploit this stochastic energy source and put together with the conventional energy sources without affecting the performance of existing electrical grids, several research projects have been achieved. In addition, at ocean level, wind energy has a great potential. It means that the production of this energy will increase in the world. The optimal extraction of this energy source needs to be connected to the grid via a voltage source converter which plays the role of interface. To minimise losses due to the transport of energy at very long distances, the technology called High Voltage Direct Current based on Voltage Source Converter (VSC-HVDC) is used. To achieve this goal, a new topology is designed with a new control algorithm based on control of power generated by the wind farm, the DC voltage regulation and the synchronization between wind farm and VSC-HVDC (based on NPC). The proposed topology and its control technique are validated using the "MATLAB/Simulink program". The results are promising, because the THD is less than 5% and the power factor is close to one.

  8. Relative localization in wireless sensor networks for measurement of electric fields under HVDC transmission lines.

    Science.gov (United States)

    Cui, Yong; Wang, Qiusheng; Yuan, Haiwen; Song, Xiao; Hu, Xuemin; Zhao, Luxing

    2015-02-04

    In the wireless sensor networks (WSNs) for electric field measurement system under the High-Voltage Direct Current (HVDC) transmission lines, it is necessary to obtain the electric field distribution with multiple sensors. The location information of each sensor is essential to the correct analysis of measurement results. Compared with the existing approach which gathers the location information by manually labelling sensors during deployment, the automatic localization can reduce the workload and improve the measurement efficiency. A novel and practical range-free localization algorithm for the localization of one-dimensional linear topology wireless networks in the electric field measurement system is presented. The algorithm utilizes unknown nodes' neighbor lists based on the Received Signal Strength Indicator (RSSI) values to determine the relative locations of nodes. The algorithm is able to handle the exceptional situation of the output permutation which can effectively improve the accuracy of localization. The performance of this algorithm under real circumstances has been evaluated through several experiments with different numbers of nodes and different node deployments in the China State Grid HVDC test base. Results show that the proposed algorithm achieves an accuracy of over 96% under different conditions.

  9. A Pilot Directional Protection for HVDC Transmission Line Based on Relative Entropy of Wavelet Energy

    Directory of Open Access Journals (Sweden)

    Sheng Lin

    2015-07-01

    Full Text Available On the basis of analyzing high-voltage direct current (HVDC transmission system and its fault superimposed circuit, the direction of the fault components of the voltage and the current measured at one end of transmission line is certified to be different for internal faults and external faults. As an estimate of the differences between two signals, relative entropy is an effective parameter for recognizing transient signals in HVDC transmission lines. In this paper, the relative entropy of wavelet energy is applied to distinguish internal fault from external fault. For internal faults, the directions of fault components of voltage and current are opposite at the two ends of the transmission line, indicating a huge difference of wavelet energy relative entropy; for external faults, the directions are identical, indicating a small difference. The simulation results based on PSCAD/EMTDC show that the proposed pilot protection system acts accurately for faults under different conditions, and its performance is not affected by fault type, fault location, fault resistance and noise.

  10. Nonlinear Control of Back-to-Back VSC-HVDC System via Command-Filter Backstepping

    Directory of Open Access Journals (Sweden)

    Jie Huang

    2017-01-01

    Full Text Available This paper proposed a command-filtered backstepping controller to improve the dynamic performance of back-to-back voltage-source-converter high voltage direct current (BTB VSC-HVDC. First, the principle and model of BTB VSC-HVDC in abc and d-q frame are described. Then, backstepping method is applied to design a controller to maintain the voltage balance and realize coordinated control of active and reactive power. Meanwhile, command filter is introduced to deal with the problem of input saturation and explosion of complexity in conventional backstepping, and a filter compensation signal is designed to diminish the adverse effects caused by the command filter. Next, the stability and convergence of the whole system are proved via the Lyapunov theorem of asymptotic stability. Finally, simulation results are given to demonstrate that proposed controller has a better dynamic performance and stronger robustness compared to the traditional PID algorithm, which also proves the effectiveness and possibility of the designed controller.

  11. HVDC-AC system interaction from AC harmonics. Volume 1. Harmonic impedance calculations. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Breuer, G D; Chow, J H; Lindh, C B; Miller, N W; Numrich, F H; Price, W W; Turner, A E; Whitney, R R

    1982-09-01

    Improved methods are needed to characterize ac system harmonic behavior for ac filter design for HVDC systems. The purpose of this General Electric Company RP1138 research is to evaluate the present filter design practice and to investigate methods for calculating system harmonic impedances. An overview of ac filter design for HVDC systems and a survey of literature related to filter design have been performed. Two methods for calculating system harmonic impedances have been investigated. In the measurement method, an instrumentation system for measuring system voltage and current has been assembled. Different schemes of using the measurements to calculate system harmonic impedances have been studied. In the analytical method, a procedure to include various operating conditions has been proposed. Computer programs for both methods have been prepared, and the results of the measurement and analytical methods analyzed. A conclusion of the project is that the measurement and analytical methods both provided reasonable results. There are correlations between the measured and analytical results for most harmonics, although there are discrepancies between the assumptions used in the two methods. A sensitivity approach has been proposed to further correlate the results. From the results of the analysis, it is recommended that both methods should be tested further. For the measurement method, more testing should be done to cover different system operating conditions. In the analytical method, more detailed models for representing system components should be studied. In addition, alternative statistical and sensitivity approaches should be attempted.

  12. HVDC-AC system interaction from AC harmonics. Volume 1. Harmonic impedance calculations. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Breuer, G D; Chow, J H; Lindh, C B; Miller, N W; Numrich, F H; Price, W W; Turner, A E; Whitney, R R

    1982-09-01

    Improved methods are needed to characterize ac system harmonic behavior for ac filter design for HVDC systems. The purpose of this General Electric Company RP1138 research is to evaluate the present filter design practice and to investigate methods for calculating system harmonic impedances. An overview of ac filter design for HVDC systems and a survey of literature related to filter design have been performed. Two methods for calculating system harmonic impedances have been investigated. In the measurement method, an instrumentation system for measuring system voltage and current has been assembled. Different schemes of using the measurements to calculate system harmonic impedances have been studied. In the analytical method, a procedure to include various operating conditions has been proposed. Computer programs for both methods have been prepared, and the results of the measurement and analytical methods analyzed. A conclusion of the project is that the measurement and analytical methods both provided reasonable results. There are correlations between the measured and analytical results for most harmonics, although there are discrepancies between the assumptions used in the two methods. A sensitivity approach has been proposed to further correlate the results. From the results of the analysis, it is recommended that both methods should be tested further. For the measurement method, more testing should be done to cover different system operating conditions. In the analytical method, more detailed models for representing system components should be studied. In addition, alternative statistical and sensitivity approaches should be attempted.

  13. A new simplified adaptive control scheme for multi-terminal HVDC transmission systems

    Energy Technology Data Exchange (ETDEWEB)

    Meah, Kala [Electrical and Computer Engineering, York College of Pennsylvania, York, PA 17405 (United States); Ula, A.H.M. Sadrul [Electrical and Computer Engineering, University of Wyoming, Laramie, WY 82071 (United States)

    2010-05-15

    This paper proposes a new control scheme for multi-terminal HVDC (MTDC) systems to improve the performance during the system transients such as AC line faults. The new method is called parallel multi-proportional-integral (MPI) control scheme. This new control scheme provides wide range of controller parameters and has the ability to response quickly. To evaluate the performance of the proposed control scheme, a four-terminal HVDC system is considered with the detailed modeling of converters, commutation transformers, source impedances, line parameters, and filters. Simulation results from various transient conditions are compared between the proposed controller, the fuzzy logic-based auto-tuning PI controller, and the conventional fixed-parameter PI controller. The SimPowerSystems and the fuzzy logic toolboxes in the MATLAB/SIMULINK software package are used to conduct the simulations. Simulation results show that the MPI controller has better performance than the conventional fixed-parameter PI controller and has very similar responses compared to the fuzzy logic-based auto-tuning PI controller without any added complexity in controller design procedure for a MTDC system. (author)

  14. 高压直流换流站噪声预测与控制研究%Study on the Noise Prediction and Control for HVDC Converter Stations

    Institute of Scientific and Technical Information of China (English)

    阮学云; 张明发; 李志远; 魏浩征

    2013-01-01

    高压直流换流站由于单体设备噪声大,数量多且分散,对周边的环境噪声影响大,因此需要进行噪声治理。为达到噪声控制目标,不仅要对换流站的各控制方案进行噪声预测对比计算,还要尽可能提高预测精度。针对目前主要噪声源设备声功率级难以确定,对噪声预测精度影响较大的难题,提出一种具有实用价值的实地测量与噪声预测软件计算相结合的方法。高压直流换流站噪声控制主要从合理选择站址、优化总平面布置、降低声源、采用换流变前增设隔声屏障、交流滤波电抗器采用低噪声电抗器、在交流滤波器周围围墙上设置轻型隔声吸声屏障等方面采取措施。运用Sound Plan对某一高压换流站进行噪声预测分析,并在治理结束后进行实地测量,结果表明:采取上述措施后,敏感点达标,对敏感点影响的厂界测点达标,且预测值和实测值误差在0~2 dB(A)范围内,实现环境效益和经济效益和谐发展。%Due to the strong noise, numerous and scattered equipments,HVDC has great influence on the surrounding acoustic environment, therefore it needs to carry out the noise control.In order to achieve the goal of noise control, HVDC is not only to develop predicting each control scheme's computation, but also as far as possible to improve the prediction accuracy. At present, the main noise source equipment of sound power level is difficult to determine, however noise prediction accuracy is greatly influenced by this problem, so this paper presents an new approach which is combining with the field measurements and noise prediction calculation software. Noise treatment schemes must take measures in proper site selection,optimum general layout,sound source reduction, sound barrier in front of converter transformers,using low noise reactor in AC filter reactor and installing light sound insulation and sound barrier on walls

  15. 新型双馈入直流输电系统供电无源网络的运行特性研究%Operation Characteristic Research on Novel Double-Infeed HVDC System Supplying Passive Network

    Institute of Scientific and Technical Information of China (English)

    郭春义; 赵成勇; 王晶

    2012-01-01

    A novel double-infeed HVDC system, combining a conventional high voltage direct current transmission (HVDC) and voltage-source converter based HVDC (VSC-HVDC), is proposed in this paper for supplying an entirely passive AC network. The detailed model for starting HVDC using VSC-HVDC is provided and control strategies of the whole system are designed. Aiming to validate the steady state and dynamic performance of the double-infeed HVDC system, the process of starting HVDC using VSC-HVDC and the dynamic performance of double-infeed HVDC when three-phase to ground fault occurring at HVDC inverter side are investigated. PSCAD/EMTDC Simulation results show that, the proposed double-Infeed HVDC system can supply power to passive network and it also has favorable dynamic and fault-restoration performance.%提出由传统高压直流输电系统(HVDC)和电压源换流器高压直流输电系统(VSC-HVDC)组成的新型双馈入直流输电系统(Double-InfeedHVDC)向无源网络输送电能。建立了利用VSC-HVDC启动HVDC的详细模型,并设计了Double-InfeedHVDC的控制系统。为了研究该双馈入直流输电系统的稳态和暂态性能,分别针对VSC-HVDC启动HVDC的特性和HVDC逆变侧发生三相短路故障时的特性进行了研究。PSCAD/EMTDC下的仿真结果表明,Double-InfeedHVDC系统可以为无源网络供电,同时具有良好的动态和故障恢复性能。

  16. Operating characteristic analysis of a 400 mH class HTS DC reactor in connection with a laboratory scale LCC type HVDC system

    Science.gov (United States)

    Kim, Sung-Kyu; Kim, Kwangmin; Park, Minwon; Yu, In-Keun; Lee, Sangjin

    2015-11-01

    High temperature superconducting (HTS) devices are being developed due to their advantages. Most line commutated converter based high voltage direct current (HVDC) transmission systems for long-distance transmission require large inductance of DC reactor; however, generally, copper-based reactors cause a lot of electrical losses during the system operation. This is driving researchers to develop a new type of DC reactor using HTS wire. The authors have developed a 400 mH class HTS DC reactor and a laboratory scale test-bed for line-commutated converter type HVDC system and applied the HTS DC reactor to the HVDC system to investigate their operating characteristics. The 400 mH class HTS DC reactor is designed using a toroid type magnet. The HVDC system is designed in the form of a mono-pole system with thyristor-based 12-pulse power converters. In this paper, the investigation results of the HTS DC reactor in connection with the HVDC system are described. The operating characteristics of the HTS DC reactor are analyzed under various operating conditions of the system. Through the results, applicability of an HTS DC reactor in an HVDC system is discussed in detail.

  17. Parasabella Bush, 1905, replacement name for the polychaete genus Demonax Kinberg, 1867 (Annelida, Polychaeta, Sabellidae

    Directory of Open Access Journals (Sweden)

    María Tovar-Hernández

    2010-10-01

    Full Text Available Parasabella Bush, 1905 is reintroduced as a replacement name for Demonax Kinberg, 1867 (Annelida: Polychaeta: Sabellidae which is a junior homonym of Demonax Thomson, 1860 (Insecta: Coleoptera: Cerambycidae.

  18. Condition Monitoring of HV Bushings in the Presence of Missing Data Using Evolutionary Computing

    CERN Document Server

    Dhlamini, Sizwe M; Marwala, Tshilidzi

    2007-01-01

    The work proposes the application of neural networks with particle swarm optimisation (PSO) and genetic algorithms (GA) to compensate for missing data in classifying high voltage bushings. The classification is done using DGA data from 60966 bushings based on IEEEc57.104, IEC599 and IEEE production rates methods for oil impregnated paper (OIP) bushings. PSO and GA were compared in terms of accuracy and computational efficiency. Both GA and PSO simulations were able to estimate missing data values to an average 95% accuracy when only one variable was missing. However PSO rapidly deteriorated to 66% accuracy with two variables missing simultaneously, compared to 84% for GA. The data estimated using GA was found to classify the conditions of bushings than the PSO.

  19. Understanding the causes of bush encroachment in Africa: The key to effective management of savanna grasslands

    Directory of Open Access Journals (Sweden)

    Olaotswe E. Kgosikoma

    2013-12-01

    Full Text Available The increase in biomass and abundance of woody plant species, often thorny or unpalatable, coupled with the suppression of herbaceous plant cover, is a widely recognized form of rangeland degradation. Bush encroachment therefore has the potential to compromise rural livelihoods in Africa, as many depend on the natural resource base. The causes of bush encroachment are not without debate, but fire, herbivory, nutrient availability and rainfall patterns have been shown to be the key determinants of savanna vegetation structure and composition. In this paper, these determinants are discussed, with particular reference to arid and semi-arid environments of Africa. To improve our current understanding of causes of bush encroachment, an integrated approach, involving ecological and indigenous knowledge systems, is proposed. Only through our knowledge of causes of bush encroachment, both direct and indirect, can better livelihood adjustments be made, or control measures and restoration of savanna ecosystem functioning be realized.

  20. K-Dimension and H(o)lder Exponent for Bush Type Fractal Functions

    Institute of Scientific and Technical Information of China (English)

    Wang Hongyong

    2006-01-01

    Bush type fractal functions were defined by means of the expression of Cantor series of real numbers. The upper and lower bound estimates for the K-dimension of such functions were given. In a typical case, the fractal dimensional relations in which the K-dimension equals the box dimension and packing dimension were presented; moreover, the exact H(o)lder exponent were obtained for such Bush type functions.

  1. Measurement of Contact Conditions between Suction-Side Bush and Blade in Swing Compressor

    Science.gov (United States)

    Tanaka, Shinji; Ito, Yasutaka; Nakahara, Tsunamitsu; Kyogoku, Keiji

    This paper describes an application of an electrical contact resistance method to measure contact conditions of sliding parts between a suction-side bush and a blade in a swing compressor, and examined the contact conditions under some operating conditions. In addition, solid contact ratios between the suction-side bush and the blade were calculated from the measured results of contact conditions. The solid contact ratios were compared with those of a vane tip in a rotary compressor. The results indicate that the sliding parts between the suction-side bush and the blade are in the mixed lubrication condition that the solid contact occurs in fluid lubrication. An upper edge side of the suction-side bush is noncontact even though discharge pressure or operating frequency of the compressor increases. Solid contact between a lower edge side of the suction-side bush and the blade increases with an increase of discharge pressure or a decrease of operating frequency of the compressor. The solid contact ratio between the suction side bush and the blade is less than that of the vane tip.

  2. Development of Partial Discharge Sensing Device for Epoxy Resin Bushing

    Science.gov (United States)

    Mutakamihigashi, Tatsuya; Kawasaki, Makoto; Hashiba, Yasuhito

    For the electric power equipment and the cables, prevention of accident is very important. And in substations, a lot of solid insulations using epoxy resin are introduced into cubicle-type switchgears because of its high insulation reliability and down-sizing ability. We know a phenomenon that partial discharge occur when electric installation have degraded. When void or crack exist in the polymer insulating materials or interface of conductor, partial discharge is caused and finally results in breakdown. In recent years, the feature is seen in the partial discharge generated in the epoxy resin before and after the progress of electric tree by our research. Electro-magnetic wave spectra radiated from partial discharge have specific frequency region from 200MHz to 450MHz. We developed the sensing device that can detect the electric discharge by receiving the signal by mobile antenna. We proved the performance of this equipment in operating substations; As a result, partial discharge in epoxy resin was detected by electro-magnetic wave. And then, we removed epoxy resin bushing from the cubicle and measured partial discharge by discharging current, we confirmed that presumed level is correct.

  3. Modeling and Simulation Analysis on HVDC Snubber%高压直流缓冲器的建模分析及应用

    Institute of Scientific and Technical Information of China (English)

    屈鲁; 李格

    2016-01-01

    HVDC snubber is a transformer-like short-circuit current suppression device. It can suppress and interrupt short-circuit current of HVDC transmission effectively combined with HVDC circuit-breaker. In this paper, HVDC snubber model is developed by adopting nonlinear resistance and nonlinear inductance in parallel based on its nonlinear equivalent circuit. Then experiment and simulation are conducted to verify HVDC snubber performance, and results show that HVDC snubber can effectively suppress short-circuit current and reduce arcing time. Dynamic response of its non-linear equivalent circuit is also analyzed, and results show that HVDC snubber can suppress short circuit current effectively only in over-damping state. Finally, a hybrid HVDC short-circuit protection scheme is proposed, combining HVDC snubber and HVDC circuit-breaker, and its feasibility is analyzed.%高压直流缓冲器是一种类变压器的直流短路电流抑制装置,结合高压直流断路器可有效地抑制、切断直流输电系统中的短路电流。首先基于高压直流缓冲器的等效电路,采用非线性电阻和非线性电感并联的方法建立其等效模型;接着对高压直流缓冲器的工作性能进行了实验验证和仿真验证,结果表明高压直流缓冲器能够有效地抑制短路电流的峰值和燃弧时间;然后对高压直流缓冲器的非线性等效电路进行动态响应分析,分析结果表明高压直流缓冲器只有工作于过阻尼状态才能有效地抑制短路电流;最后结合高压直流缓冲器和高压直流断路器,提出一种混合式高压直流短路保护方案,并对其可行性进行了分析。

  4. Grid-connection of offshore wind farms using VSC-HVDC systems

    Energy Technology Data Exchange (ETDEWEB)

    Fu, Xiaofan; Dessaint, Louis A. [Ecole de Technologie Superieure, Montreal, QC (Canada). Dept. of Electrical Engineering; Gagnon, Richard [Hydro-Quebec Research Institute, Montreal, QC (Canada)

    2011-07-01

    In this paper, the structure of variable speed PMSG-based offshore wind farms connected to the grid through VSC-HVDC link is presented. And the system models are developed. Also, the corresponding control strategy for this system is proposed. The control objective of the generator side VSC is to achieve the optimal wind power by adjusting the speed of permanent magnet synchronous generator, while the grid side VSC is to maintain DC voltage constant. Furthermore, a case study of 100MW offshore wind farm consisting of 50 individual 2MW PSMG-based wind turbines is developed in MATLAB/SimPowerSystems. Simulation results show the proposed scheme works well. (orig.)

  5. Control and Protection of Wind Power Plants with VSC-HVDC Connection

    DEFF Research Database (Denmark)

    Chaudhary, Sanjay

    Wind power plants are the fastest growing source of renewable energy. The European Union expects to generate 230 GW wind power, in which the offshore wind power is expected to contribute 40 GW. Offshore wind power plants have better wind velocity profile leading to a higher energy yield. Europe has...... a huge potential of offshore wind energy, which is a green and sustainable resource. All these have led to the development of offshore wind power plants. However, overall cost of the offshore installation, operation, and maintenance are higher than those of the onshore wind power plants. Therefore...... oscillations, and hence, lower dc voltage overshoots in the VSC-HVDC system. On the protection side, the coordination of over-current relays has been analysed in the new environment. A simple yet reliable scheme utilizing the well-known over-current relay characteristics has been presented for the detection...

  6. Fault Locating in HVDC Transmission Lines Using Generalized Regression Neural Network and Random Forest Algorithm

    Directory of Open Access Journals (Sweden)

    M. Farshad

    2013-09-01

    Full Text Available This paper presents a novel method based on machine learning strategies for fault locating in high voltage direct current (HVDC transmission lines. In the proposed fault-location method, only post-fault voltage signals measured at one terminal are used for feature extraction. In this paper, due to high dimension of input feature vectors, two different estimators including the generalized regression neural network (GRNN and the random forest (RF algorithm are examined to find the relation between the features and the fault location. The results of evaluation using training and test patterns obtained by simulating various fault types in a long overhead transmission line with different fault locations, fault resistance and pre-fault current values have indicated the efficiency and the acceptable accuracy of the proposed approach.

  7. Control system of the physical simulation for the HVDC transmission system

    Science.gov (United States)

    Liu, Zheng; Huang, Tongyuan; Liu, Wei; Ai, Bing; Mou, Daohuai

    2007-12-01

    The intention of this paper is to present the control system of the physical simulation for the Three Gorges HVDC transmission system. It covers all essential control functions which are involved in the continuously working power flow control and power modulation including converter firing and pole current control. This system include two convert stations, They design the fault arbitrator for the dual-controller system based on fault-tolerant technology and figure-safety-comparing technology. The arbitrator can endure long working time with high reliability. Controller A and B not only works independent, but also can controlled by the master controller from CAN bus. At the same time, because the master controller is a industrial PC, we can easy adjust and enhance the functions. This characteristic is especially fit the physical simulation system.

  8. Cost estimation of HVDC transmission system of Bangka’s NPP candidates

    Energy Technology Data Exchange (ETDEWEB)

    Liun, Edwaren, E-mail: edwaren@batan.go.id; Suparman, E-mail: edwaren@batan.go.id [Centre for Nuclear Energy Development, National Nuclear Energy Agency of Indonesia (Indonesia)

    2014-09-30

    Regarding nuclear power plant development in Bangka Island, it can be estimated that produced power will be oversupply for the Bangka Island and needs to transmit to Sumatra or Java Island. The distance between the regions or islands causing considerable loss of power in transmission by alternating current, and a wide range of technical and economical issues. The objective of this paper addresses to economics analysis of direct current transmission system to overcome those technical problem. Direct current transmission has a stable characteristic, so that the power delivery from Bangka to Sumatra or Java in a large scale efficiently and reliably can be done. HVDC system costs depend on the power capacity applied to the system and length of the transmission line in addition to other variables that may be different.

  9. Cost and Benefit Analysis of VSC-HVDC Schemes for Offshore Wind Power Transmission

    Institute of Scientific and Technical Information of China (English)

    Sheng WANG; Chunmei FENG; An WEN; Jun LIANG

    2013-01-01

    Due to low load factors of wind power generation,it is possible to reduce transmission capacity to minimize the cost of transmission system construction.Two VSC-HVDC schemes for offshore wind farm,called the point to point (PTP) and DC mesh connections are compared in terms of the utilization of transmission system and its cost.A Weibull distribution is used for estimating offshore wind power generation,besides,the cross correlation between wind farms is considered.The wind energy curtailment is analyzed using the capacity output possibility table (COPT).The system power losses,costs of transmission investment and wind energy curtailment are also computed.A statistic model for the wind generation and transmission is built and simulated in MATLAB to validate the study.It is concluded that a DC mesh transmission can reduce the energy curtailment and power losses.Further benefit is achievable as the wind cross correlation between wind farms decreases.

  10. Integration of a finite element generator model into a simulated HVDC connected system

    Energy Technology Data Exchange (ETDEWEB)

    Preston, T.W.; Sturgess, J.P. [GEC Alsthom Engineering Research Center, Stafford (United Kingdom)

    1994-12-31

    Within most system analysis programs generators and motors are represented by an equivalent circuit model either a 2-axis model for both stators and rotor or a three-phase model of the stator and a two-axis model of the rotor. This may be adequate under certain operating conditions such as steady-state or some symmetrical faults but for inverter-fed motors or generators feeding into a rectified load a more rigorous model of the machine is required. This paper describes the theory and development of such a model, its integration with the power electronics and application to 6-pulse and 12-pulse converters, the latter being appropriate in systems similar to HVDC unit connection. (author) 5 refs., 16 figs.

  11. Disturbance Attenuation of DC Voltage Droop Control Structures in a Multi-Terminal HVDC Grid

    DEFF Research Database (Denmark)

    Thams, Florian; Chatzivasileiadis, Spyros; Prieto-Araujo, Eduardo

    2017-01-01

    of the disturbance rejection of these droop control structures. The approach is based on multi-variable frequency response analysis where both ac and dc grid dynamics are incorporated. In particular, the amplification of dc voltage oscillations due to wind power variations is analyzed using singular value analysis......DC voltage droop control is seen as the preferred control structure for primary voltage control of future multiterminal HVDC systems. Different droop control structures have been proposed in literature which can be classified in eight categories. This paper contributes to an analysis....... Further, the impact of dc cable modeling on the results is discussed. In addition, it is shown that the maximum singular value limits, frequently used in literature for MIMO-analysis, are not sufficient to prove that the impact of certain disturbances on analyzed outputs is within a certain boundary...

  12. Capacitor voltage ripple reduction and arm energy balancing in MMC-HVDC

    DEFF Research Database (Denmark)

    Martin-Loeches, Ruben Sánches; Parikh, Harsh; Tsolaridis, Georgios

    2016-01-01

    Modular Multilevel Converters are emerging and widely used in HVDC applications. However, the submodule capacitors are still large and the energy balancing under unbalanced conditions is a challenge. In this paper, an analytical model focusing on the energy stored in the capacitors and voltage...... variations is utilized in order to achieve better performance. By injecting a second order harmonic component into the circulating current, the energy variation and consequently the capacitor voltage ripple is reduced allowing for a capacitor size reduction. At the same time, an arm energy balancing...... controller has been proposed which uses the first harmonic of the circulating current in order to keep the energy balance of the leg under internal unbalanced conditions....

  13. Investigation of Hybrid Bipolar HVDC System Performances%混合双极高压直流输电系统的特性研究

    Institute of Scientific and Technical Information of China (English)

    郭春义; 赵成勇; Allan Montanari; Aniruddha M. Gole; 肖湘宁

    2012-01-01

    为了充分发挥电网换相换流器高压直流输电系统 (line commutated converter based high voltage direct current,LCC—HVDC)和电压源换流器高压直流输电系统(voltagesourceconverterbasedHVDC,VSC.HVDC)的优势,针对~种新型的混合双极高压直流输电系统(hybridbipolarbasedhighvoltagedirectcurrent,HB—HVDC)进行了研究,该系统的正极是传统的12脉动LCC.HVDC系统,而负极是VSC—HVDC系统。建立了由LCC正极和VSC负极组成的混合双极高压直流输电系统的模型,推导了其在稳态时的数学模型,并设计了正负极之间的协调控制策略。在PSCAD/EMTDC环境下对HB—HVDC系统的稳态和暂态运行特性进行了研究分析。最后对HB—HVDC系统和闭锁负极VSC—HVDC后LCC—HVDC系统的运行特性进行了对比研究。结果表明:HB-HVDC系统可以更好地调节交流母线电压,减少LCC极换相失败的可能性,并且具有快速的故障恢复能力;同时也证明所设计的协调控制策略可以有效地改善HB—HVDC系统的稳态和动态特性。%A new hybrid bipolar high voltage direct current system (HB-HVDC) was investigated to synthetically utilize the advantages of line commutated converter based HVDC (LCC-HVDC) and voltage source converter based HVDC (VSC-HVDC). The positive pole was a conventional 12-pulse LCC-HVDC system and the negative pole was a VSC-HVDC system. The model of HB-HVDC was developed, and its steady-state mathematical model was deduced. Then the coordinated control strategy between positive pole LCC-HVDC and negative pole VSC-HVDC was designed. The operation performances of HB-HVDC system in steady and transient state were studied. Finally, the performances of the HB-HVDC system were compared with an identical LCC- HVDC with VSC-HVDC blocked. The results show that HB- HVDC system has a better regulation for AC busbar voltage, makes the LCC-HVDC less susceptible to commutation

  14. Electrical and electromagnetic investigations for HVDC ground electrode sites in India

    Science.gov (United States)

    Manglik, A.; Verma, S. K.; Muralidharan, D.; Sasmal, R. P.

    High Voltage Direct Current (HVDC) power transmission systems require setting up of specially designed ground electrodes at terminal ends of the transmission line to close the circuit with an earth return path. The design parameters of these electrodes need the information about the electrical conductivity structure within a radius and depth of several km of the site in order to ensure that the injected current penetrates deep enough into the earth. Further, detailed conductivity structure, up to 100-200 m depth, of the electrode site covering an area of less than a sq. km is also needed to ensure safe limits for the step and touch potential at the site. Electrical and electromagnetic methods are very useful tools for this purpose. However, artificial source variants such as deep direct current (DC) resistivity sounding pose logistic problems for target depths greater than a couple of kilometers and in inaccessible areas. We have employed magnetotelluric (MT) and electrical resistivity tomography (ERT) tools to investigate the detailed deep and shallow electrical conductivity structure, respectively, of several potential sites in India for a ±800 kV, 6000 MW HVDC multi-terminal system. Investigations of a site in Assam revealed the presence of highly resistive crustal rocks at the depth of about 1.3 km beneath a thick pile of conductive sediments, rendering the site unsuitable even though the shallow conductivity was favorable. At another site identified after analyzing available geological and geophysical data, we inferred the presence of conductive structure up to at least 4.0 km depth. ERT investigation at this site revealed a favorable conductive structure except for the presence of a 20-m-thick near-surface resistive layer. This information has been useful for the electrode design. We suggest that a strategy suitably combining MT and ERT is useful in the selection of ground electrode sites.

  15. Development of toroid-type HTS DC reactor series for HVDC system

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Kwangmin, E-mail: kwangmin81@gmail.com [Changwon National University, 55306 Sarim-dong, Changwon 641-773 (Korea, Republic of); Go, Byeong-Soo; Park, Hea-chul; Kim, Sung-kyu; Kim, Seokho [Changwon National University, 55306 Sarim-dong, Changwon 641-773 (Korea, Republic of); Lee, Sangjin [Uiduk University, Gyeongju 780-713 (Korea, Republic of); Oh, Yunsang [Vector Fields Korea Inc., Pohang 790-834 (Korea, Republic of); Park, Minwon; Yu, In-Keun [Changwon National University, 55306 Sarim-dong, Changwon 641-773 (Korea, Republic of)

    2015-11-15

    Highlights: • The authors developed the 400 mH, 400 A class toroid-type HTS DC reactor system. • The target temperature, inductance and operating current are under 20 K at magnet, 400 mH and 400 A, respectively. All target performances of the HTS DC reactor were achieved. • The HTS DC reactor was conducted through the interconnection operation with a LCC type HVDC system. • Now, the authors are studying the 400 mH, 1500 A class toroid-type HTS DC reactor for the next phase HTS DC reactor. - Abstract: This paper describes design specifications and performance of a toroid-type high-temperature superconducting (HTS) DC reactor. The first phase operation targets of the HTS DC reactor were 400 mH and 400 A. The authors have developed a real HTS DC reactor system during the last three years. The HTS DC reactor was designed using 2G GdBCO HTS wires. The HTS coils of the toroid-type DC reactor magnet were made in the form of a D-shape. The electromagnetic performance of the toroid-type HTS DC reactor magnet was analyzed using the finite element method program. A conduction cooling method was adopted for reactor magnet cooling. The total system has been successfully developed and tested in connection with LCC type HVDC system. Now, the authors are studying a 400 mH, kA class toroid-type HTS DC reactor for the next phase research. The 1500 A class DC reactor system was designed using layered 13 mm GdBCO 2G HTS wire. The expected operating temperature is under 30 K. These fundamental data obtained through both works will usefully be applied to design a real toroid-type HTS DC reactor for grid application.

  16. Linealización de sistemas VSC-HVDC para el diseño de un controlador PI vectorial

    Directory of Open Access Journals (Sweden)

    Nelson Díaz Aldana

    2014-01-01

    Full Text Available Los sistemas VSC-HVDC son muy utilizados para la transmisión de energía en redes de interconexión eléctrica. Uno de los principales problemas que poseen estos sistemas es la complejidad de su modelo matemático, lo que conlleva grandes dificultades para el diseño de controladores que permitan la regulación de parámetros como la tensión DC de transmisión, así como la potencia activa y reactiva del sistema VSC-HVDC. En este artículo se presenta la linealización de un sistema VSC-HVDC y el posterior diseño de un controlador lineal PI vectorial a partir del modelo linealizado. Adicionalmente, se proponen dos estrategias para la validación de este tipo de controladores, la primera consiste en un único controlador PI para regular los estados del sistema para cada VSC, la segunda consiste en el diseño de controladores PI vectoriales independientes para la regulación de cada estado del VSC.

  17. Effects of hedgerows on bats and bush crickets at different spatial scales

    Science.gov (United States)

    Lacoeuilhe, Aurélie; Machon, Nathalie; Julien, Jean-François; Kerbiriou, Christian

    2016-02-01

    Biodiversity is threatened by the loss and fragmentation of habitats. The role of hedgerows in maintaining biodiversity is well established, but few studies have addressed the importance for biodiversity of the intrinsic characteristics of hedgerows and the quality of hedgerow networks along a spatial scale. We examined three quality indices providing information at different territorial levels: density in the landscape, structural diversity and wood production. We performed an acoustic survey in a grassland to estimate the species abundance and community composition of bats (9 taxa) and bush crickets (11 species). Using an approach based on species and traits, we assessed how hedgerow quality influenced the activity of these taxa at different spatial scales (from 50 to 1000 m) and focused on three types of traits: bush cricket mobility ability, bat foraging strategy and habitat specialization. In general, our results showed the importance of hedgerow quality for bats and bush crickets, but the strength of the association between taxa and hedgerows varied substantially among the species and the spatial scales. Although it depends on the taxa, the production, density and structural diversity of hedgerows each had an overall positive effect. Our results suggested that these effects were generally more important at large scales. The scale effect of the production index is the best predictor of activity for bat and bush cricket taxa and traits. Our results showed the importance of hedgerow quality for the ecology of bat and bush cricket communities and could be used to improve conservation management.

  18. Application of desirability function for optimizing the performance characteristics of carbonitrided bushes

    Directory of Open Access Journals (Sweden)

    Boby John

    2013-06-01

    Full Text Available The performance of a product is generally characterized by more than one response variable. Hence the management often faces the problem of simultaneous optimization of many response variables. This study was undertaken to simultaneously optimize the surface hardness and case depth of carbonitrided bushes. Even though lots of literature has been published on various methodologies for tackling the multi-response optimization problem, the simultaneous optimization of heat treated properties of carbonitrided bushes are not reported yet. In this research the effect of four factors and two interactions on surface hardness and case depth of carbontirded bushes were studied using design of experiments. Based on the experimental results, the expected values of the heat treated properties of the bushes were estimated for all possible combination of factors. Then the best combination which, simultaneously optimized the response variables, was arrived at using desirability function. The study showed that the optimum combination obtained through desirability function approach not only minimized the variation around the targets of surface hardness and case depth but also was superior to the ones obtained by optimizing the response variables separately. Moreover this study provides a useful and effective approach to design the production process to manufacture bushes with customer specified surface hardness and case depth targets.

  19. A Quantitative Evaluation Method on Interaction Analysis of Hybrid Multi-infeed HVDC System%混合多馈入直流输电系统相互作用关系的定量评估方法

    Institute of Scientific and Technical Information of China (English)

    郭春义; 倪晓军; 赵成勇

    2016-01-01

    Apparent increase in short circuit ratio (AISCR) is an index to quantitatively evaluate the impact of voltage source converter based high voltage direct current (VSC-HVDC) on line commutated converter based high voltage direct current (LCC-HVDC) in hybrid mutli-infeed HVDC system. Based on the AISCR index, the impact of VSC-HVDC on LCC-HVDC was further studied considering different power flow direction of VSC-HVDC link. Then, the transient performances of LCC-HVDC, such as transient over-voltage, commutation failure immunity and fault recovery performances, were investigated in PSCAD/EMTDC software, when VSC operates as rectifier or inverter. Considering the electric distance between VSC-HVDC and LCC-HVDC, the trend of AISCR was calculated with varying distance. Finally, the coupling effects of AC system and VSC-HVDC on AISCR of LCC-HVDC were decoupled, and the AISCR impacted by VSC-HVDC only, without the impact of AC system, was obtained. The conclusions got could provide valuable theoretical guide for capacity and feed-in location selection of VSC-HVDC in hybrid multi-infeed HVDC system.%视在短路比增加量(apparent increase in short circuit ratio,AISCR)是一种定量评估混合多馈入系统中电压源换流器型高压直流输电(voltage source converter based high voltage direct current,VSC-HVDC)对电网换相换流器高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)运行特性影响关系的指标,该文基于AISCR指标,定量评估混合双馈入系统中当VSC-HVDC潮流方向不同时对LCC-HVDC运行特性的影响,在此基础上基于PSCAD/EMTDC对比分析VSC分别作为整流运行和逆变运行时LCC-HVDC的暂态过电压、换相失败抵御能力、故障恢复等暂态运行特性。研究当 VSC-HVDC 与LCC-HVDC之间存在电气距离的情况下AISCR随着电气距离的变化趋势;最后将交流系统与 VSC-HVDC 对LCC-HVDC 视在短路比增加量的耦合作用进行了

  20. Pauvreté et politique sociale : le bilan des années Bush  Poverty and Public Policy: An Assessment of the Bush Years

    Directory of Open Access Journals (Sweden)

    Taoufik Djebali

    2010-03-01

    Full Text Available Neuf jours après son investiture, G. W. Bush lançait son programme relatif aux Faith-Based Initiatives (FBI, une partie prenante de son « conservatisme compatissant ». Les FBI constituent une rupture avec la tradition monétariste reaganienne, même si elles s’appuient sur le rejet de l’État et la réduction du budget social. Le rôle des FBI est d’aider les organisations caritatives, notamment religieuses, à s’investir davantage dans le travail social.  Le bilan de la politique sociale de G. Bush est plutôt mitigé. La pauvreté a fortement augmenté et les promesses budgétaires en faveur des Faith-Based Organizations n’ont pas été tenues. Pire, les accusations contre les dérives des FBI fusent. L’administration Bush est accusée d’avoir utilisé les FBI et l’argent public pour obtenir des gains politiques et mettre en place un système de financement occulte en faveur des républicains et leurs alliés.Nine days after he was sworn in, Bush launched his social program, the Faith-Based Initiatives (FBI, a major component of his “compassionate conservatism.” The FBI constituted a break with the Reagan monetarist tradition, even if they are motivated by the withdrawal of the State and the reduction of the social budget. The role of the FBI is to help charities, in particular religious organizations, to invest more in social work. On the whole, the social policy implemented during the Bush years is evaluated negatively. Poverty increased rapidly and the financial promises in favor of the Faith-Based Organizations were not kept. Worse, new revelations have been disclosed. The Bush administration is accused of having used the FBI and public money to make political gains and set up an obscure funding system that benefited the Republicans and their political allies.

  1. Influence of temperature on Cole-Cole dielectric model of oil-immersed bushing

    Science.gov (United States)

    Wang, K.; Chen, X. J.; Xu, X. W.; Liu, G. Q.; Zou, D. X.; Liu, W. D.

    2017-07-01

    In this paper, 72.5 kV oil-immersed bushing was produced in laboratory. The frequency-domain dielectric response tests of oil-immersed bushings were carried out at different test temperatures. The experimental data were fitted by using the modified double relaxation Cole-Cole dielectric model. The influence of temperature variation on the dielectric response test of the oil-immersed bushing and the Cole-Cole dielectric model parameters were analysed. The results showed that with the increase of the test temperature, the spectrum of the real and imaginary of the complex permittivity are shifted to the high frequency direction; the parameters of the dielectric model are significantly affected by temperature.

  2. 关于一类Bush型分形曲面的维数分析%DIMENSION ANALYSIS ON A CLASS OF BUSH TYPE FRACTAL SURFACES

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    In this paper,the authors construct a class of fractal surfaces,Bush type surfaces,based on the Bush type functions.The Box dimension,Packing dimension and Hausdorff dimension of such surfaces are investigated.

  3. "One More Time, Let Me Justify This War": An Analysis of President Bush's Declaration of Days of Thanksgiving.

    Science.gov (United States)

    Jones, Kevin T.

    President Bush's declaration of April 5-7, 1991 as National Days of Thanksgiving is a unique example of Presidential civil religious discourse: no other President has ever made such a declaration to thank God for a victory in war. Whether he intended to or not, President Bush engaged in a rhetorical form which allowed him to manipulate a very…

  4. Systematic notes on Asian birds. 1. A review of the russet bush-warbler Bradypterus seebohmi (Ogilvie-Grant, 1895)

    NARCIS (Netherlands)

    Dickinson, E.C.; Rasmussen, P.C.; Round, P.D.; Rozendaal, F.G.

    2000-01-01

    The bush-warbler Bradypterus mandelli (Brooks, 1875) was described from Sikkim, and numerous specimens from India were identified with it, but it was synonymised with the brown bush-warbler Bradypterus luteoventris (Hodgson, 1845) in 1881. In 1952, east Asian populations were grouped under the name

  5. Systematic notes on Asian birds. 1. A review of the russet bush-warbler Bradypterus seebohmi (Ogilvie-Grant, 1895)

    NARCIS (Netherlands)

    Dickinson, E.C.; Rasmussen, P.C.; Round, P.D.; Rozendaal, F.G.

    2000-01-01

    The bush-warbler Bradypterus mandelli (Brooks, 1875) was described from Sikkim, and numerous specimens from India were identified with it, but it was synonymised with the brown bush-warbler Bradypterus luteoventris (Hodgson, 1845) in 1881. In 1952, east Asian populations were grouped under the name

  6. Description of the nest, eggs, and nestling of Rufous-bellied Bush-Tyrants ( Myiotheretes fuscorufus )

    OpenAIRE

    Londoño, Gustavo Adolfo

    2015-01-01

    The Myiotheretes bush-tyrants are a small clade of Neotropical flycatchers (family: Tyrannidae) localized to narrow elevational strips in the Andes Mountains. Here, we describe the first reported nest of Rufous-bellied Bush-Tyrants (Myiotheretes fuscorufus). It was a large cup nest lined with Usnea lichen and elevated on a sheltered rock ledge behind a flowering Puya bromeliad at 2,985 m asl in the buffer zone of Manu National Park, Peru. We provide a near-complete history of the nest from eg...

  7. VSC—HVDC在风电场并网系统中的应用研究%A survey of VSC - HVDC for wind farm interconnection

    Institute of Scientific and Technical Information of China (English)

    肖小兵; 周杰娜; 袁旭峰; 姚刚; 何肖蒙

    2012-01-01

    介绍风力发电并网对电网产生的影响,分析说明VSC—HVDC的工作原理和技术特点,并对风电场联网VSC—HVDC控制器设计进行阐述,列举VSC~HVDC的应用场合,并且举例介绍国外采用VSC—HVDC在风电并网中的应用。%The impact of the wind farm interconnection is described, then the working principle and the technical characteristics of VSC - HVDC are analyzed and explained, and then the design of the wind farm interconnection with VSC - HVDC controller is described, finally a list of application in VSC - HVDC controll on wind farm intergration is listed together with illustrated examples.

  8. A finite element analysis of a large thrust elastic metal-plastics bearing bush for a hydraulic turbine

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Presents the study on the pressure and friction fields of the lubricant film on the surface of a large thrust elastic metal-plastic bearing bush in a hydraulic turbine using the method of finite element analysis and the stress and displacement fields in the vertical direction of the bush surface obtained to provide a theoretical basis for the design of contour lines and investigation into the causes for destruction of bushes, and concludes with test results that 1 ) the stress on the surface of the bush is not uniform; 2) a tension stress tends to occur near the oil ingress and egress edges but it is minor; 3) the biggest displacement in the vertical direction appears where x = 84 and Y = 1 153 and has a value of 0.022 mm; 4) the deformation of the bearing bush is harmful to the maintenance of lubricant film.

  9. System Aspects and Modulation Strategies of an HVDC-based Converter System for Wind Farms

    Energy Technology Data Exchange (ETDEWEB)

    Meier, Stephan

    2009-05-15

    In this thesis, a new HVDC-based converter system for wind farms is investigated. It is based on a mutually commutated soft-switching converter system and provides a unique integrated solution for the wind turbine generator drive systems, the wind turbine interconnection, and the power conversion for HVDC transmission. In a wind farm, the mutually commutated converter system is a distributed system. A medium-frequency collection grid connects the converter station, equipped with a single-phase voltage source converter and a medium-frequency transmission transformer, with the wind turbines, each containing a cyclo converter and a medium-frequency distribution transformer. In this thesis, various system aspects regarding the application of a distributed mutually commutated converter system in a wind farm are investigated. Special attention is paid to the design of a medium-frequency collection grid that has an acceptable level of transient over voltages, the design of medium-frequency transformers with suitable magnetic, electric and thermal properties, and the development of a strategy to commutate the voltage source converter during low power generation. In order to adapt the mutually commutated converter system for an application in a wind farm, it had to be further developed. Different carrier-based and space-vector oriented modulation methods have been investigated. It turns out that for any load angle there is a quasi-discontinuous pulse width modulation strategy that can produce the same pulse patterns as space vector modulation. In addition, a modulation strategy has been developed that allows to replace the IGBTs in the cyclo converter with cheap, robust, and reliable fast thyristors, despite their absence of turn-off capability. The feasibility of different modulation strategies for mutually commutated converter systems has been verified on a down-scaled prototype converter system with both IGBT- and thyristor-based cyclo converters. Finally, a feasible

  10. Simulation of HVDC light system based on MATLAB%基于 MATLAB 的轻型直流输电系统的仿真

    Institute of Scientific and Technical Information of China (English)

    冯媛硕; 宋吉江; 沙宏哲

    2015-01-01

    轻型直流输电(HVDC Light)是一种新型的输电技术,以电压源换流器(VSC)为核心,控制上采用脉宽调制技术( PWM)以达到高可控性直流输电的目的。文章首先分析了轻型直流输电系统的基本结构和原理,然后利用MATLAB仿真软件建立一个三电平轻型直流输电系统的仿真模型,最后对仿真结果进行分析,仿真结果表明建立的轻型直流输电系统具有较好的稳定精度和响应速度。文章为将来研究轻型直流输电系统的物理模型奠定了一定的理论基础。%HVDC Light is a new technology of DC transmission, in which VSC ( Voltage Source Converter) acted as the core.Control system adopts the PWM technique to reach the high controllable DC transmission.Firstly, the basic structure and fundamental principle of the HVDC Light system were introduced briefly.Then, a simulation model for the typical three-level HVDC Light power transmission system was built on MATLAB.The simulation results were ana-lyzed at last.The simulation results show that the HVDC Light system has good stabilization accuracy and response speed.This study provides a theoretical basis for further research on the physical model of the HVDC Light system.

  11. VSC-HVDC的次同步阻尼特性研究%Study on sub-synchronous damping characteristic of VSC-HVDC

    Institute of Scientific and Technical Information of China (English)

    徐坤; 赵成勇; 高本锋

    2012-01-01

    目前针对基于电压源换流器(Voltage Source Converter)的高压直流输电技术(VSC-HVDC)的研究,主要集中在控制策略方面,而研究VSC-HVDC对相邻发电机组阻尼特性的影响较少.从VSC-HVDC的工作原理出发,阐述了VSC-HVDC的能够抑制次同步振荡的机理.采用基于时域实现的复转矩系数法-测试信号法,分析了机组作用系数、控制方式以及有功、无功功率水平对VSC-HVDC阻尼特性的影响.针对同一交流系统,对比分析了VSC-HVDC与传统的HVDC的阻尼特性的大小.研究结果表明,与传统HVDC相比,VSC-HVDC能够显著改善相邻发电机组的次同步阻尼特性.%The study on the HVDC based on voltage-source converter focuses mainly on the control strategy while less on the impact of electrical damping on the adjacent units by VSC-HVDC. The mechanism of VSC-HVDC on inhibiting sub-synchronous oscillation is analyzed theoretically in the respect of its operation principle. Then the complex torque coefficient method, namely the test signal method, which is realized by time domain simulation, is adopted to investigate the impact of the unit interaction factor, control mode, active power level and reactive power level on the electrical damping on the adjacent units. Finally, adopting the same system, the damping of VSC-HVDC and HVDC are compared using test signal method.

  12. Mould and mycotoxin exposure assessment of melon and bush mango seeds, two common soup thickeners consumed in Nigeria.

    Science.gov (United States)

    Ezekiel, Chibundu N; Sulyok, Michael; Somorin, Yinka; Odutayo, Foluke I; Nwabekee, Stella U; Balogun, Afeez T; Krska, Rudolf

    2016-11-21

    An examination of the mould and fungal metabolite pattern in melon and bush mango seeds locally produced in Nigeria was undertaken in order to understand the mycotoxicological risk posed to consumers of both of these important and commonly consumed soup thickeners. The variation in mycotoxin levels in graded categories of both foodstuffs were also determined. Aspergillus, Fusarium, Penicillium, Mucorales and Trichoderma were the recovered fungi from the foodstuffs with Aspergillus species dominating (melon=97.8%; bush mango=89.9%). Among the Aspergillus species identified Aspergillus section Flavi dominated (melon: 72%; bush mango: 57%) and A. flavus, A. parasiticus, A. parvisclerotigenus and A. tamarii were the recovered species. About 56% and 73% of the A. flavus isolates from melon and bush mango seed samples, respectively were aflatoxigenic. Thirty-four and 59 metabolites including notable mycotoxins were found in the melon and bush mango seeds respectively. Mean aflatoxin levels (μg/kg) in melon (aflatoxin B1 (AFB1)=37.5 and total aflatoxins=142) and bush mango seeds (AFB1=68.1 and total aflatoxins=61.7) were higher than other mycotoxins, suggesting potential higher exposure for consumer populations. Significantly (pmycotoxins were found in hand-peeled melon and discoloured bush mango seeds than in machine-peeled melon and non-discoloured seeds except for HT-2 and T-2 toxins which occurred conversely. All melon and bush mango seeds exceeded the 2μg/kg AFB1 limit whereas all melon and 55% of bush mango seeds exceeded the 4μg/kg total aflatoxin EU limit adopted in Nigeria. This is the first report of (1) mycotoxin co-occurrence in bush mango seeds, (2) cyclopiazonic acid, HT-2 toxin, moniliformin, mycophenolic acid, T-2 toxin and tenuazonic acid occurrence, and (3) mycotoxin exposure assessment of both foodstuffs.

  13. Interaction of Droop Control Structures and its Inherent Effect on the Power Transfer Limits in Multi-terminal VSC-HVDC

    DEFF Research Database (Denmark)

    Thams, Florian; Eriksson, Robert; Molinas, M.

    2016-01-01

    Future multi-terminal HVDC systems are expected to utilize dc voltage droop controllers and several control structures have been proposed in literature. This paper proposes a methodology to analyse the impact of various types of droop control structures using small-signal stability analysis...... to disturbances for all the implementations. A case study analyzing a three terminal HVDC VSC-based grid with eight different kinds of droop control schemes points out that three control structures outperform the remaining ones. Additionally, a multi-vendor case is considered where the most beneficial...

  14. Summarization for Development and Application Status of HVDC Technology%HVDC技术的发展应用情况综述

    Institute of Scientific and Technical Information of China (English)

    赵国梁; 吴涛

    2006-01-01

    HVDC(高压直流输电)技术在我国具有广阔的应用前景.本文对HVDC的特点及其发展应用情况,我国HVDC工程建设的国产化情况,HVDC在我国的应用前景,以及多端HVDC、轻型HVDC和电容换相换流器(CCC)等新型HVDC技术的发展应用情况进行综述.

  15. VSC-HVDC输电系统特点与应用%Characteristics and application of VSC-HVDC power transmission system

    Institute of Scientific and Technical Information of China (English)

    孟垂懿; 鲍洁秋; 武录

    2012-01-01

    随着半导体技术和新能源发电的发展,出现了基于VSC(Voltage Sourced Converters)技术的新型直流输电系统——轻型直流输电(HVDC Light),在介绍HvDC Light基本原理基础上,从结构和功能上与传统直流输电技术进行对比,阐述了HVDC Light的优点,并对其应用作了总结和展望.

  16. Hard- and software of real time simulation tools of Electric Power System for adequate modeling power semiconductors in voltage source convertor based HVDC and FACTS

    Directory of Open Access Journals (Sweden)

    Ufa Ruslan A.

    2014-01-01

    Full Text Available The motivation of the presented research is based on the needs for development of new methods and tools for adequate simulation of Flexible Alternating Current Transmission System (FACTS devices and High Voltage Direct Current Transmission (HVDC system as part of real electric power systems (EPS. For that, a hybrid approach for advanced simulation of the FACTS and HVDC based on Voltage Source is proposed. The presented simulation results of the developed hybrid model of VSC confirm the achievement of the desired properties of the model and the effectiveness of the proposed solutions.

  17. La politique commerciale de George W. Bush : rupture ou continuité ? American Trade Policy under George W. Bush: Continuity or Change?

    Directory of Open Access Journals (Sweden)

    Jean-Baptiste Velut

    2010-03-01

    Full Text Available Cet article se propose de dresser un bilan critique de la politique commerciale du Président George W. Bush. Dans un premier temps, il compare les perspectives idéologiques et les ambitions politiques du leader républicain à celles de son prédécesseur démocrate, Bill Clinton, avant de mettre l’accent sur les nouvelles données du contexte politique et économique des années 2000. Ces éléments introductifs serviront de fondations, d’une part, pour l’étude de la gestion des relations commerciales entre les États-Unis et leurs principaux partenaires économiques, et d’autre part pour l’analyse de la stratégie de « libéralisation compétitive » adoptée par George W. Bush aux niveaux multilatéral, régional et bilatéral. L’objectif est double : déterminer les lignes de rupture et de continuité entre le président républicain et son prédécesseur ; et établir un bilan des principales initiatives commerciales lancées par l’administration Bush dans le but de mieux comprendre les nouveaux défis intérieurs et internationaux auxquels son successeur sera confronté.This article offers a critical assessment of American trade policy under George W. Bush. It begins by comparing his views and political ambitions with those of his Democratic predecessor, Bill Clinton, before highlighting the new political and economic context of the 2000s. These elements provide crucial background, first to study the evolution of America’s relations with its top trading partners and second to analyze the strategy of “competitive liberalization” undertaken by the administration at the multilateral, regional and bilateral levels. This article has two objectives: 1 determining trends of continuity and change between George W. Bush and his predecessor; 2 assessing the trade policy initiatives undertaken by the Republican administration in order to understand the domestic and international challenges with which the next President

  18. Development of toroid-type HTS DC reactor series for HVDC system

    Science.gov (United States)

    Kim, Kwangmin; Go, Byeong-Soo; Park, Hea-chul; Kim, Sung-kyu; Kim, Seokho; Lee, Sangjin; Oh, Yunsang; Park, Minwon; Yu, In-Keun

    2015-11-01

    This paper describes design specifications and performance of a toroid-type high-temperature superconducting (HTS) DC reactor. The first phase operation targets of the HTS DC reactor were 400 mH and 400 A. The authors have developed a real HTS DC reactor system during the last three years. The HTS DC reactor was designed using 2G GdBCO HTS wires. The HTS coils of the toroid-type DC reactor magnet were made in the form of a D-shape. The electromagnetic performance of the toroid-type HTS DC reactor magnet was analyzed using the finite element method program. A conduction cooling method was adopted for reactor magnet cooling. The total system has been successfully developed and tested in connection with LCC type HVDC system. Now, the authors are studying a 400 mH, kA class toroid-type HTS DC reactor for the next phase research. The 1500 A class DC reactor system was designed using layered 13 mm GdBCO 2G HTS wire. The expected operating temperature is under 30 K. These fundamental data obtained through both works will usefully be applied to design a real toroid-type HTS DC reactor for grid application.

  19. Coordinated control of multiple HVDC links using input-output exact linearization

    Energy Technology Data Exchange (ETDEWEB)

    Eriksson, Robert; Knazkins, Valerijs; Soeder, Lennart [Royal Institute of Technology (KTH), Electric Power Systems, Teknikringen 33, 100 44 Stockholm (Sweden)

    2010-12-15

    This paper is concerned with the investigation of a new control technique for the conventional High Voltage Direct Current (HVDC) link. The proposed technique relies upon nonlinear state feedback linearization of the AC/DC power system. The idea in input-output exact feedback linearization is to algebraically transform nonlinear systems dynamics into a linear control problem using a nonlinear pre-feedback loop, and then for the linearized power system one can design another feedback loop using a well established technique such as a linear-quadratic regulator. The primary goal of the controller presented in this paper is to contribute to the enhancement of both the transient and the small-signal stability of the power system. Since the proposed state feedback linearization does not rely on the assumption that there is only small deviation of the states from an equilibrium, the enhancement of both is feasible. The simulation results obtained in the framework of the study show that the proposed controller is capable of stabilizing the system in various system operating conditions. (author)

  20. An Annotated Bibliography of HVDC Transmission and FACTS Devices, 1996-1997.

    Energy Technology Data Exchange (ETDEWEB)

    Litzenberger, Wayne H.; Varma, Rajiv K.; Flanagan, John D. [eds.

    1998-06-01

    This edition of the Annotated Bibliography of HVDC Transmission and FACTS Devices continues work begun in 1962 by the late Erik Bromberg, Bonneville Power Administration Librarian. His original bibliography covered the period 1932--1962. Subsequent editions were compiled by Bromberg, Val S. Lava, and Wayne Litzenberger, all of Bonneville Power Administration. Beginning with the 1991--1993 edition, the scope of the bibliography was expanded to include flexible ac transmission (FACTS) devices. This 1996--1997 edition also contains information for 1998. Preparation of the present edition took place primarily in May-June of 1998. All pertinent references have been included that were available to the editors at the time of preparation. Papers for the 1998 IEEE Winter and Summer Power Meetings and 1998 T and D Conference have been included. This edition contains the organizational affiliation of the first-named author as an aid to accessing the reference. Unfortunately, space limitations prevented the inclusion of the affiliations of all authors. Some minor editorial changes have been made to abstracts to ensure consistency in style and syntax.

  1. Bush keeldub vägede Iraagist taandumise tähtajaga nõustumast

    Index Scriptorium Estoniae

    2007-01-01

    USA president George Bush pani veto Kongressis heaks kiidetud seadusele, mille kohaselt eraldataks sõjapidamiseks Iraagis veel 100 miljardit dollarit, kuid tingimusel, et USA vägede väljatoomist alustataks sel aastal ning see lõppeks 2008. aasta 31. märtsiks

  2. Bush jättis püüne Putinile / Toomas Alatalu

    Index Scriptorium Estoniae

    Alatalu, Toomas, 1942-

    2007-01-01

    Politoloog tõdeb, et USA president George W. Bush lahkus enne lõppu Aasia-Vaikse ookeani majanduskoostöö organisatsiooni (APEC) tippkohtumiselt ja külastas Iraaki, et kinnitada maailmale Iraagi sõja vajalikkust. Vene president Vladimir Putin tugevdas Vene positsioone maailmas, andes krediiti Indoneesiale Vene laevade ja lennukite ostuks ning sõlmides uraaniostulepingu Austraaliaga

  3. The political impact of WTO rules : steel tariffs and the Bush administration / William L Burns

    Index Scriptorium Estoniae

    Burns, William L

    2004-01-01

    USA president George W. Bush kuulutas märtsis 2002 välja 30-protsendilise tolli kehtestamise suurele osale teraseimpordist eesmärgiga aidata Ameerika terasetööstusel kohaneda välismaise terase sisseveoga. Poliitiliselt mõjuvõimas Ühendriikide terasetööstus on tollide rakendamist nõudnud juba neli aastat

  4. effect of bush burning on herbaceous plant diversity in lagos state ...

    African Journals Online (AJOL)

    conducted to assess the effect of bush burning on plant species diversity. Three frequently ... Data obtained for plants were compared using % frequency, % stand and Simpson and ... species are destroyed by fire and can become locally extinct if fire is too ..... unplanned fire in a semi-arid rangeland of South Africa. Journal ...

  5. Putin, Bush issue statement on advancing US-Russian human contacts

    CERN Document Server

    2002-01-01

    "In addition to interstate, bilateral, regional and global issues discussed by Russian President Vladimir Putin and US President George Bush during their Kremlin summit on 24 May, the two leaders considered issues related to people-to-people contacts, ties between cities, states and regions, institutions and organizations" (1 page).

  6. Bush mõistis hukka moslemite vägivaldsed meeleavaldused / Kaarel Kaas

    Index Scriptorium Estoniae

    Kaas, Kaarel, 1978-

    2006-01-01

    USA president Georg W. Bush ja välisminister Condoleezza Rice mõistavad hukka moslemite vägivaldsed meeleavaldused, kuid mitte nende ajendiks olnud Muhamedi pilavad karikatuurid ning leiavad, et Iraan ja Süüria kasutavad pilapiltide skandaali oma poliitiliste eesmärkide saavutamiseks

  7. A Functional Analysis of the 1988 Bush-Dukakis Presidential Debates.

    Science.gov (United States)

    Benoit, William L.; Brazeal, LeAnn M.

    2002-01-01

    Applies the Functional Theory of Political Campaign Discourse to the 1988 presidential debates between George Bush and Michael Dukakis. Challenges the notion that this campaign was mostly negative. Concludes that despite the belief that modern campaigns are devoid of substance, these debates stressed policy about twice as much as character. (SG)

  8. William Bennett and the "Good War" against Drugs: Doublespeak and the Bush Administration's Hidden Agenda.

    Science.gov (United States)

    Massey, Tom

    This paper contends that former Secretary of Education William Bennett's "war on drugs" (he now directs the government's campaign against drugs) is not being waged against those who sell and use drugs, but against the civil liberties of everyone. The paper maintains that under the guise of ridding society of what President Bush called…

  9. Superheroes and the Bush doctrine: narrative and politics in post­-9/11 discourse

    NARCIS (Netherlands)

    Hassler-Forest, D.A.

    2011-01-01

    Dan Hassler-Forest onderzocht de manier waarop de Amerikaanse politiek samenvloeit met populaire cultuur. De centrale figuur hierin is de superheld, die fungeert als een symbolische belichaming voor de conflicterende fantasieën die de jaren van het presidentschap van George W. Bush in de Verenigde S

  10. Obamas opgør med Bush låser ham i dronekrig

    DEFF Research Database (Denmark)

    Ulrich, Philip Christian

    2013-01-01

    En helt central del af Obamas valgkamp i 2008 var et opgør med dele af Bush administrationens krig mod terror. Obama er dog blevet fanget i en kontroversiel dronepolitik på grund af hans manglende succes med de indenrigspolitiske aspekter af opgøret...

  11. William Bennett and the "Good War" against Drugs: Doublespeak and the Bush Administration's Hidden Agenda.

    Science.gov (United States)

    Massey, Tom

    This paper contends that former Secretary of Education William Bennett's "war on drugs" (he now directs the government's campaign against drugs) is not being waged against those who sell and use drugs, but against the civil liberties of everyone. The paper maintains that under the guise of ridding society of what President Bush called…

  12. Acoustic analysis reveals a new cryptic bush-cricket in the Carpathian Mountains (Orthoptera, Phaneropteridae).

    Science.gov (United States)

    Iorgu, Ionuţ Ştefan

    2012-01-01

    A new morphologically cryptic species of phaneropterid bush-cricket from the genus Isophya is described from the Eastern Carpathian Mountains: Isophya dochiasp. n. Sound analysis and morphological details are discussed in the paper comparing the new species with several Isophya species having similar morphology and acoustic behavior.

  13. I'm Not Sure What George Bush Has to Do with Hitler

    Science.gov (United States)

    Pogorelskin, Alexis

    2005-01-01

    Alexis Pogorelskin, an associate professor at the University of Minnesota Duluth and chair of the History Department, recounts her experience in 2004 after making a controversial comment in her History of the Holocaust and 20th Century Russia class. Her comment was in reference to President Bush making no mention in the 2000 campaign about the…

  14. George W. Bush at Goree Island: American Slavery and the Rhetoric of Redemption

    Science.gov (United States)

    Medhurst, Martin J.

    2010-01-01

    On July 8, 2003, at Goree Island, Senegal, George W. Bush delivered the most important speech on American slavery since Abraham Lincoln. As an example of rhetorical artistry, the speech is a masterpiece, putting the brutality of slavery into historical, political, and theological perspective. Although the speech had deliberative effects--it grew…

  15. The political impact of WTO rules : steel tariffs and the Bush administration / William L Burns

    Index Scriptorium Estoniae

    Burns, William L

    2004-01-01

    USA president George W. Bush kuulutas märtsis 2002 välja 30-protsendilise tolli kehtestamise suurele osale teraseimpordist eesmärgiga aidata Ameerika terasetööstusel kohaneda välismaise terase sisseveoga. Poliitiliselt mõjuvõimas Ühendriikide terasetööstus on tollide rakendamist nõudnud juba neli aastat

  16. Obamas opgør med Bush låser ham i dronekrig

    DEFF Research Database (Denmark)

    Ulrich, Philip Christian

    2013-01-01

    En helt central del af Obamas valgkamp i 2008 var et opgør med dele af Bush administrationens krig mod terror. Obama er dog blevet fanget i en kontroversiel dronepolitik på grund af hans manglende succes med de indenrigspolitiske aspekter af opgøret...

  17. Superheroes and the Bush doctrine: narrative and politics in post­-9/11 discourse

    NARCIS (Netherlands)

    Hassler-Forest, D.A.

    2011-01-01

    Dan Hassler-Forest onderzocht de manier waarop de Amerikaanse politiek samenvloeit met populaire cultuur. De centrale figuur hierin is de superheld, die fungeert als een symbolische belichaming voor de conflicterende fantasieën die de jaren van het presidentschap van George W. Bush in de Verenigde

  18. Southern Methodist's Bush-Library Deal Mollifies Some Critics, but Doubts Persist about Think Tank

    Science.gov (United States)

    Glenn, David

    2008-01-01

    Southern Methodist University has released the terms of its agreement with the George W. Bush Presidential Library Foundation to house the president's official library and museum. To some faculty members, the most troubling element of the project is a conservative policy institute that will be affiliated with the library and museum. Unlike similar…

  19. Wonderful Walls

    Science.gov (United States)

    Greenman, Jim

    2006-01-01

    In this article, the author emphasizes the importance of "working" walls in children's programs. Children's programs need "working" walls (and ceilings and floors) which can be put to use for communication, display, storage, and activity space. The furnishings also work, or don't work, for the program in another sense: in aggregate, they serve as…

  20. Ambiguous walls

    DEFF Research Database (Denmark)

    Mody, Astrid

    2012-01-01

    The introduction of Light Emitting Diodes (LEDs) in the built environment has encouraged myriad applications, often embedded in surfaces as an integrated part of the architecture. Thus the wall as responsive luminous skin is becoming, if not common, at least familiar. Taking into account how wall...

  1. Innovations in the field of high-voltage direct current transmission (HVDC); Innovationen in der Hochspannungs-Gleichstrom-Uebertragungstechnik

    Energy Technology Data Exchange (ETDEWEB)

    Mukherjee, A.; Kurze, W.; Schramm, H.H.; Pereira, M.; Storner, C.; Ammon, J.; Plewka, G.; Wild, E. [Siemens AG, Erlangen (Germany). Bereich Energieuebertragung und -verbreitung; Uder, M. [Siemens AG, Erlangen (Germany). Bereich Automatisierungs- und Antriebstechnik; Schaller, G. [Erlangen-Nuernberg Univ. (Germany)

    1998-10-05

    This paper describes some new developments from different fields of HVDC technology: The use of direct light-triggered thyristors instead of the conventional electrically triggered ones; a new hybrid-optical measuring method for direct currents at high voltage potential in place of conventional transducers of zeroflux type; a new type of HVDC SF{sub 6}-circuit-breaker, developed for use as Metallic Return Transfer Breaker (MRTB), combining all advantages of an SF{sub 6}-breaker against an air-blast breaker; active filters using power electronics - as a purposeful supplement to passive filters - to reduce the harmonics to negligible levels; the new pulse-echo monitoring system for electrode lines offering a number of advantages over conventional systems (e.g. impedance measurement). All these new but successfully tested techniques and equipment go to enhance the reliability and economy of HVDC systems and therefore set future trends. (orig.) [Deutsch] An ausgewaehlten Beispielen aus verschiedenen Gebieten der HGUe-Technik berichten die Verfasser ueber einige Neuentwicklungen, z.B.: den Einsatz von direkt lichtzuendbaren Thyristoren anstelle von elektrisch zuendbaren; ein neues hybrid-optisches Gleichstrom-Messsystem im Vergleich mit konventionellen Messmethoden mit Nullflusswandlern; SF{sub 6}-Gleichstromschalter - anstelle von Druckluftschaltern beim Einsatz als Metallic Return Transfer Breaker (MRTB); aktiver Filter mit leistungselektronischen Komponenten - als Ergaenzung zu passiven Filtern zur Daempfung von Oberschwingungen ein neues Puls-Echo-Ueberwachungssystem fuer HGUe-Elektrodenleitungen, das bisherigen Methoden, z.B. Impedanzmessung, deutlich ueberlegen ist. Alle diese neuen aber erfolgreich erprobten Techniken erhoehen die Zuverlaessigkeit und Wirtschaftlichkeit von HGUe-Anlagen und sind daher zukunftsweisend. (orig.)

  2. Optimal PowerFlow (OPF) Model with Unified AC-DC Load Flow and Optimal Commitmentfor an AC-catenary Railway Power Supply System (RPSS) fed by aHigh Voltage DC (HVDC) transmission line

    OpenAIRE

    Abrahamsson, Lars; Östlund, Stefan; Söder, Lennart

    2012-01-01

    In this paper an alternative railway power systems design based on an HVDC feeder is studied. The HVDC feeder is connected to the catenary by converters. Such an HVDC line is also appropriate for DC-fed railways and AC-fed railways working at public frequency. A unit commitment optimal power flow model has been developed and is applied on a test system. In this paper, the model is presented in detail. The model, in the form of an MINLP program, uses unified AC-DC power flow to minimize the en...

  3. Steady-state model for simulating VSC based HVDC%VSC-HVDC的稳态模型仿真研究

    Institute of Scientific and Technical Information of China (English)

    张兴然; 王霞

    2007-01-01

    介绍了轻型直流输电(VSC-HVDC)技术的稳态运行特性,针对VSC-HVDC的稳态情况,设计了VSC-HVDC的控制策略,并基于PID控制原理设计了相应的控制器.仿真实验表明,该方法控制效果良好,对于故障情况能有很快的响应且稳定性良好.

  4. The General Programmer for HVDC Techniques%高压直流输电技术综述

    Institute of Scientific and Technical Information of China (English)

    王德忠

    2004-01-01

    本文介绍了目前国内外高压直流输电技术(HVDC)的发展概况及其应用情况,从技术性、经济性、可靠性等诸方面比较了交、直流输电方式的特点,肯定了HVDC技术的优越性.文章还介绍了HVDC的单极、双极、同极联络线的结构,及一个双极HVDC系统的主要元器件及其功能.

  5. Active Power Control with Undead-Band Voltage & Frequency Droop for HVDC Converters in Large Meshed DC Grids

    DEFF Research Database (Denmark)

    Vrana, Til Kristian; Zeni, Lorenzo; Fosso, Olav Bjarte

    A new control method for large meshed HVDC grids has been developed, which helps to keep the active power balance at the AC and the DC side. The method definition is kept wide, leaving the possibility for control parameter optimisation. Other known control methods can be seen as specific examples...... the band, but not set to zero as with a regular dead-band. It operates with a minimum of required communication. New converters can be added to the system without changing the control of the other individual converters. It is well suited to achieve high reliability standards due to the distributed control...

  6. Power-flow control and stability enhancement of four parallel-operated offshore wind farms using a line-commutated HVDC link

    DEFF Research Database (Denmark)

    Wang, Li; Wang, Kuo-Hua; Lee, Wei-Jen

    2010-01-01

    This paper presents an effective control scheme using a line-commutated high-voltage direct-current (HVDC) link with a designed rectifier current regulator (RCR) to simultaneously perform both power-fluctuation mitigation and damping improvement of four parallel-operated 80-MW offshore wind farms...

  7. Control Strategy of VSC-HVDC in Dual-infeed HVDC Systems%双馈入直流输电系统中VSC-HVDC的控制策略

    Institute of Scientific and Technical Information of China (English)

    赵成勇; 孙营; 李广凯

    2008-01-01

    针对多馈入直流输电(multi-infeed direct current,MIDC)系统的稳定性问题,提出将基于电压源换流器的高压直流输电(voltage source converter based HVDC,VSC-HVDC)引入到MIDC系统中,用以改善MIDC系统公共连接母线的电压特性.建立HVDC和VSC-HVDC双馈入系统的物理模型,导出相应的数学模型.并通过坐标变换得出VSC功率传输方程的直角坐标形式.采用多变量非线性控制的逆系统方法,设计VSC-HVDC系统的非线性控制器.PSCAD/EMTDC 环境下的仿真实验表明,所设计的VSC-HVDC非线性控制器不仅能有效改善VSC-HVDC的动态特性,而且在交流系统发生扰动时能有效稳定系统电压,减少HVDC逆变站发生换相失败的几率,提高HVDC系统的运行可靠性.

  8. Wall Turbulence.

    Science.gov (United States)

    Hanratty, Thomas J.

    1980-01-01

    This paper gives an account of research on the structure of turbulence close to a solid boundary. Included is a method to study the flow close to the wall of a pipe without interferring with it. (Author/JN)

  9. Droop Control Strategy for Wind Power Decentralized Integration Based on VSC-HVDC Systems%基于 VSC-HVDC 的风电分散并网下垂控制策略

    Institute of Scientific and Technical Information of China (English)

    田园园; 廖清芬; 刘涤尘; 彭思成; 邹宏亮

    2016-01-01

    With the large-scale development of offshore wind power,the voltage source converter based high voltage direct current(VSC-HVDC) transmission system has received extensive attention in recent years.By introducing the AC voltage droop control,a coordinated multi-terminal grid-connection control strategy for a wind farm AC-dispersed at the sending end based on VSC-HVDC systems is proposed.Based on the traditional control strategy for the flexible HVDC transmission system,the DC voltage control of inverters on the grid side is retained to guarantee system power balance,while AC voltage droop control rather than the original constant-power control is designed for the rectifier on the wind farm side to achieve the advantage of communication-free and reasonable dynamic allocation.Simulation analysis shows that the control strategy proposed is not only able to achieve flexible automatic tracking of rated active power,but also has certain tolerance of load fluctuation and the function of DC/AC fault isolation.And when it comes to power supply for multi-terminal distribution networks by a wind farm AC-dispersed at the sending end,quick power reversal can be achieved if the wind farm is cut out of the system to ensure power supply reliability.And the system is capable of realizing rational allocation of dynamic power automatically among them according to rated ratio,providing effective solutions for coordinated operation of wind farm”s decentralized integration into distribution networks.%海上风电的大规模开发使得柔性直流(VSC-HVDC)输电技术得到了越来越广泛的关注与应用。文中通过引入交流电压下垂控制,提出了基于 VSC-HVDC 的适应送端交流分散模式下的风电场多端并网的协调控制策略。在柔性直流输电传统控制策略的基础上,保留配电网侧逆变器的定直流电压控制,以保证系统功率平衡;而使风电场侧整流器采用交流电压下垂控制,以代替原有的恒功

  10. VSC-HVDC系统启动控制%Startup Procedures for the VSC-HVDC System

    Institute of Scientific and Technical Information of China (English)

    张静; 徐政; 陈海荣

    2009-01-01

    In order to reduce the undesired impacts and damages on the VSC-HVDC system and the connected AC system during the startup and re-startup procedures, appropriate startup control strategy should be dedicatedly designed. Charging the DC capacitor voltage to the preset value quickly is the fundamental of the subsequent control strategy. In this paper, a two-stage self startup procedure is proposed for VSC-HVDC system consisting of two-level and diode-clamped three-level converters. During the first stage, the resistors are inserted to limit the current during the charging. If the DC voltage can not reach the preset value after predetermined time, the startup procedure switches to the second stage and the capacitors will be further charged with a DC voltage controller. The startup procedure completes till the DC link voltage reaches the preset value and then the converters are ready to change from the startup mode to the normal operating mode. In addition, a new control strategy is proposed for the startup of the passive network and the AC system suffered from black out. With the proposed control strategy, the inrush currents during the energization of the transformers and the overvoltage during the closure of the long overhead transmission lines can be suppressed. Simulation results verify the feasibility of the proposed startup procedures.%合适的启动方式对减缓VSC-HVDC系统启动及重新启动时对自身和电网的冲击非常重要.如何把直流电容器电压快速提升到设定值,是后续控制策略正确工作的基础.针对目前应用较广泛的两电平和二极管钳位型三电平换流器拓扑结构,提出了一种简单、适用于VSC-HVDC系统的两阶段自励启动方法.在启动第一阶段,串接限流电阻器对直流侧电路充电;若在设定的时间内电容器电压不能达到设定值,启动转入第二阶段,即换流站在直流电压控制器的作用下对电容器继续充电,直至达到预设值,从而为换

  11. The Applicability of Traditional Protection Methods to Lines Emanating from VSC-HVDC Interconnectors and a Novel Protection Principle

    Directory of Open Access Journals (Sweden)

    Shimin Xue

    2016-05-01

    Full Text Available Voltage source converter (VSC-based high voltage direct current (VSC-HVDC interconnectors can realize accurate and fast control of power transmission among AC networks, and provide emergency power support for AC networks. VSC-HVDC interconnectors bring exclusive fault characteristics to AC networks, thus influencing the performance of traditional protections. Since fault characteristics are related to the control schemes of interconnectors, a fault ride-through (FRT strategy which is applicable to the interconnector operating characteristic of working in four quadrants and capable of eliminating negative-sequence currents under unbalanced fault conditions is proposed first. Then, the additional terms of measured impedances of distance relays caused by fault resistances are derived using a symmetrical component method. Theoretical analysis shows the output currents of interconnectors are controllable after faults, which may cause malfunctions in distance protections installed on lines emanating from interconnectors under the effect of fault resistances. Pilot protection is also inapplicable to lines emanating from interconnectors. Furthermore, a novel pilot protection principle based on the ratio between phase currents and the ratio between negative-sequence currents flowing through both sides is proposed for lines emanating from the interconnectors whose control scheme aims at eliminating negative-sequence currents. The validity of theoretical analysis and the protection principle is verified by PSCAD/EMTDC simulations.

  12. Integral Plus Resonant Sliding Mode Direct Power Control for VSC-HVDC Systems under Unbalanced Grid Voltage Conditions

    Directory of Open Access Journals (Sweden)

    Weipeng Yang

    2017-10-01

    Full Text Available An integral plus resonant sliding mode direct power control (IRSMC DPC strategy for voltage source converter high voltage direct current (VSC-HVDC systems under unbalanced grid voltage conditions is proposed in this paper. Through detailed instantaneous power flow analysis, a generalized power compensation method, by which the ratio between the amplitude of active and reactive power ripples can be controlled continuously, is obtained. This enables the system to provide flexible power control, so that the desired performance of the system on both the ac and dc sides can be attained under different operating conditions. When the grid voltage is unbalanced, one or both of the active and reactive power terms contain ripples, oscillating at twice the grid frequency, to obtain non-distorted ac current. A power controller consisting of the proportional, integral and resonant control laws is designed using the sliding mode control approach, to achieve accurate power control objective. Simulation studies on a two-terminal VSC-HVDC system using MATLAB/SIMULINK (R2013b, Mathworks, Natick, MA, USA are conducted to verify the effectiveness of the IRSMC DPC strategy. The results show that this strategy ensures satisfactory performance of the system over a wide range of operating conditions.

  13. VSC-HVDC输电系统的性能分析%Performance Analysis of Voltage Source Converter Based HVDC Transmission System

    Institute of Scientific and Technical Information of China (English)

    姜建国; 颜廷阁

    2012-01-01

    VSC-HVDC is a new type of power transmission technology developed based on traditional HVDC. Aiming at the features of VSC-HVDC system, e. g. , good controllability, compact modular design and easy to construct multi-terminal DC systems, etc, the working principle and dynamic performance are described. Meanwhile, dynamic performance analysis on the faults of 100 kV and 200 MV VSC-HVDC transmission systems is investigated. The simulation results by using Matlab/Simulink verify that the system possesses good performance and effective decoupling control under active and reactive power variations and fault conditions.%电压源型高压直流输电( VSC-HVDC)技术是在传统直流输电基础上发展起来的一种新型输电技术.针对VSC-HVDC系统具有良好的可控性、紧凑的模块化设计、容易构成多端直流系统等特点,阐述了其工作原理及动态性能.同时,探讨了100 kV、200 MVVSC-HVDC输电系统故障的动态性能分析,并采用Matlab/Simulink进行了仿真试验.试验结果证实了该系统在有功与无功变化以及在故障条件下具有性能良好和解耦控制有效的特性.

  14. Bush lubas al-Zarqawi järglase kinni püüda / Aadu Hiietamm

    Index Scriptorium Estoniae

    Hiietamm, Aadu, 1954-

    2006-01-01

    USA president George W. Bush teatas, et tapetud terrorivõrgustiku al Qaeda Iraagi haru liidri Abu Musab al-Zarqawi järglaseks nimetatud Abu Hamsa al-Muhajir on kuulutatud enim tagaotsitavaks terroristiks

  15. Bush lubas al-Zarqawi järglase kinni püüda / Aadu Hiietamm

    Index Scriptorium Estoniae

    Hiietamm, Aadu, 1954-

    2006-01-01

    USA president George W. Bush teatas, et tapetud terrorivõrgustiku al Qaeda Iraagi haru liidri Abu Musab al-Zarqawi järglaseks nimetatud Abu Hamsa al-Muhajir on kuulutatud enim tagaotsitavaks terroristiks

  16. [Brood parasitism and egg mimicry on Brownish-flanked Bush Warbler (Cettia fortipes) by Lesser Cuckoo (Cuculus poliocephalus)].

    Science.gov (United States)

    Yang, Can-Chao; Cai, Yan; Liang, Wei

    2010-10-01

    Nest fate of Brownish-flanked Bush Warbler (Cettia fortipes) was conducted in breeding seasons from 1999 to 2009 in Kuankuoshui Natural Reserve, Guizhou province. Predation rate, parasitism rate, hatching success, nesting success and reproductive success were surveyed and egg color was quantified using spectrophotometer. Principal component analysis, reflectance spectrum and Robinson Project were used to analyze the egg color of bush warbler and egg mimicry of Lesser Cuckoo (Cuculus poliocephalus) in parasitized nests. Our results indicated that the Brownish-flanked Bush Warbler suffered from high predation rate and relatively high parasitism rate of 49.26% and 9.18%, respectively. Reflectance analysis showed that the hue and chroma of Lesser Cuckoo eggs were highly mimetic but the egg brightness and ultraviolet reflectance were different from the bush warbler.

  17. Condition monitoring of oil-impregnated paper bushings using extension neural network, Gaussian mixture and hidden Markov models

    CSIR Research Space (South Africa)

    Miya, WS

    2008-10-01

    Full Text Available In this paper, a comparison between Extension Neural Network (ENN), Gaussian Mixture Model (GMM) and Hidden Markov model (HMM) is conducted for bushing condition monitoring. The monitoring process is a two-stage implementation of a classification...

  18. Advanced fault ride-through control of DFIG based wind turbines including grid connection via VSC-HVDC

    Energy Technology Data Exchange (ETDEWEB)

    Feltes, Christian

    2012-07-01

    With the growing renewable energy share in the power generation mix it becomes inevitable that also these new generation technologies participate on the provision of grid services to guarantee stable operation of the grid, especially when one considers the decreasing number of conventional power plants in operation as a result of the expansion of wind based generation plants. These so-called ancillary services include frequency / active power control, voltage / reactive power control and fault ride-through (FRT) with fast voltage control and are stipulated in modern grid codes. In the context of this thesis advanced control algorithms have been developed for wind turbines based on doubly-fed induction generator (DFIG) to allow safe FRT during symmetrical and unsymmetrical faults. This covers the control for conventional AC grid connection as well as for the connection through voltage source converter (VSC) based high voltage direct current transmission (HVDC). Currently, the DFIG is the most used generator technology in modem wind turbines, since it combines a relatively simple slip-ring induction machine with a frequency converter rated to only approx. 30% of the total power. This makes the DFIG a cost-effective concept, which offers a variable speed range and a high degree of flexibility in control. However, due to the direct coupling of the generator stator circuit to the grid, grid faults are a special challenge for the frequency converter, its protection circuits and control algorithms. As base for the detailed evaluation of the impact of grid faults to the DFIG, this thesis contains the analytical derivation of the DFIG short circuit currents under consideration of frequency converter control. The DFIG concept presented in this thesis makes use of a DC chopper in the frequency converter, which allows safe FRT with grid voltage support through both converter sides. The developed control contains a new algorithm for a clear separation and control of positive

  19. Bush Blitz aids description of three new species and a new genus of Australian beeflies (Diptera, Bombyliidae, Exoprosopini)

    OpenAIRE

    Christine Lambkin; Justin Bartlett

    2011-01-01

    Bush Blitz is a three-year multimillion dollar program to document the plants and animals in hundreds of properties across Australia’s National Reserve System. The core focus is on nature discovery – identifying and describing new species of plants and animals. The Bush Blitz program has enabled the collection and description of beeflies (Diptera, Bombyliidae) from surveys in Western Australia and Queensland. Three new species of Australian beeflies belonging to the Exoprosopini a...

  20. Earthquake Response and Isolation Layer Parameter Effect of Seismic Isolation Systems of Transformers With Bushings

    Institute of Scientific and Technical Information of China (English)

    CAO Meigen; ZHOU Fulin; TAN Ping; ZHANG Guangping; GAO Zhengguo

    2012-01-01

    Seismic damage data and experiences on power transformers at home and abroad indicate that the destruction type of high-power transformers is various and the vulnerability is very high. Furthermore, the post-disaster reconstruction of transformers, which needs a long recovery cycle and a high cost, will be very difficult. Studies have shown that the acceleration response of the transformer and bushings will be quickly reduced and seismic reliability of transformer will be improved because there is one seismic isolation layer between the bottom of transformer tank and the base which form the seismic isolation system of the transformer and bushings (SISTB). But isolation layer design and parameters selection of SISTB have larger difference with general structures.

  1. Harmonic amplitude dependent dynamic stiffness of hydraulic bushings: Alternate nonlinear models and experimental validation

    Science.gov (United States)

    Fredette, Luke; Dreyer, Jason T.; Rook, Todd E.; Singh, Rajendra

    2016-06-01

    The dynamic stiffness properties of automotive hydraulic bushings exhibit significant amplitude sensitivity which cannot be captured by linear time-invariant models. Quasi-linear and nonlinear models are therefore proposed with focus on the amplitude sensitivity in magnitude and loss angle spectra (up to 50 Hz). Since production bushing model parameters are unknown, dynamic stiffness tests and laboratory experiments are utilized to extract model parameters. Nonlinear compliance and resistance elements are incorporated, including their interactions in order to improve amplitude sensitive predictions. New solution approximations for the new nonlinear system equations refine the multi-term harmonic balance term method. Quasi-linear models yield excellent accuracy but cannot predict trends in amplitude sensitivity since they rely on available dynamic stiffness measurements. Nonlinear models containing both nonlinear resistance and compliance elements yield superior predictions to those of prior models (with a single nonlinearity) while also providing more physical insight. Suggestion for further work is briefly mentioned.

  2. The effect of mate removal on dawn singing behaviour in male pied bush chats

    Institute of Scientific and Technical Information of China (English)

    Vinaya Kumar SETHI; Dinesh BHATT; Amit KUMAR

    2011-01-01

    To determine the influence of pairing status on dawn singing behaviour in pied bush chats Saxicola caprata, we conducted mate removal experiments across eight territories. The experiment was divided into three stages: pre-removal (pairs were present on theit respective territories), removal (females were experimentally removed), and returned (females were released into the focal pairs' territories). Dawn bout length, song rate, song complexity, percentage performance time, song perch height, and distance of singing location to territory boundary were measured for each male during each experimental stage. We did not find an effect of mate removal on any dawn song characteristics of male pied bush chats suggesting that the presence or absence of a mate does not influence male dawn singing behaviour. Our findings further suggest that males use dawn chorus to mediate social relationships with neighbouring males to proclaim an established territory.

  3. (+)-Larreatricin hydroxylase, an enantio-specific polyphenol oxidase from the creosote bush (Larrea tridentata).

    Science.gov (United States)

    Cho, Man-Ho; Moinuddin, Syed G A; Helms, Gregory L; Hishiyama, Shojiro; Eichinger, Dietmar; Davin, Laurence B; Lewis, Norman G

    2003-09-16

    An enantio-specific polyphenol oxidase (PPO) was purified approximately 1,700-fold to apparent homogeneity from the creosote bush (Larrea tridentata), and its encoding gene was cloned. The posttranslationally processed PPO ( approximately 43 kDa) has a central role in the biosynthesis of the creosote bush 8-8' linked lignans, whose representatives, such as nordihydroguaiaretic acid and its congeners, have potent antiviral, anticancer, and antioxidant properties. The PPO primarily engenders the enantio-specific conversion of (+)-larreatricin into (+)-3'-hydroxylarreatricin, with the regiochemistry of catalysis being unambiguously established by different NMR spectroscopic analyses; the corresponding (-)-enantiomer did not serve as a substrate. This enantio-specificity for a PPO, a representative of a widespread class of enzymes, provides additional insight into their actual physiological roles that hitherto have been difficult to determine.

  4. Process development of making bearings and bushings from continuous-cast SAE 660 bronze alloy plate

    Science.gov (United States)

    Chill, J. L.

    A process for making bearings and bushings offers considerable potential. The ability to minimize machining and scrap loss, especially for middle and large diameter bearings, should help to lower manufacturing costs appreciably. In addition, the substantial improvement of mechanical properties resulting from rolling offers the increased performance over as-cast SAE 660 bronze bearings in terms of better load carrying ability and wear resistance.

  5. Design of 154 kV Extra-High-Voltage Prototype SF6 Bushing for Superconducting Electric Power Applications

    Science.gov (United States)

    Koo, Ja-yoon; Seong, Jae-gyu; Hwang, Jae-sang; Lee, Bang-wook; Lee, Sang-hwa

    2012-09-01

    One of the critical components to be developed for high-voltage superconducting devices, such as superconducting transformers, cables, and fault current limiters, is a high-voltage bushing to supply a high current to devices without insulation difficulties in cryogenic environments. Unfortunately, suitable bushings for high-temperature-superconductivity (HTS) equipment have not been fully developed to address cryogenic insulation issues. As a fundamental step towards developing the optimum design of the 154 kV prototype SF6 bushing of HTS devices, the puncture and creepage breakdown voltages of glass-fiber-reinforced-plastic (GFRP) were analyzed with a variety of configurations of electrodes and gap distances in the insulation material. And design factors of high-voltage cryogenic bushings were obtained from the result of tests. Finally, the withstand voltage tests of manufacturing a 154 kV extra-high-voltage (EHV) prototype bushing has been performed. Consequently, we verified the insulation level of the newly designed 154 kV EHV cryogenic prototype bushings for superconducting electric power applications.

  6. Adequacy of mineral contents of raw and plain sticky sauce of common and bush okra

    Directory of Open Access Journals (Sweden)

    Moyib Oluwasayo Kehinde

    2015-12-01

    Full Text Available In Nigeria, common okra (Abelmoschus esculentus L. and bush okra (Corchorus olitorius L. are popular mucilage vegetables used as sticky sauce for easy consumption of starchy staples.Both raw vegetables and sticky sauce of common as well as bush okra were estimated for their potential in the provision of daily dietary allowance of important minerals. Modified methods of the Association of Official Analytical Chemists (AOAC were used to estimate the assessed minerals.The results showed that the raw and sticky sauce of assessed common and bush okra contained appreciable levels and essential minerals, but are not adequate to meet recommended dietary allowance, except for Fe and Cu. Comparatively, the two species of okra varied significantly in their mineral content of the raw and plain sauce. There was also a negative effect of cooking on the mineral contents, which reduced significantly to an average of 30% on a dry weight basis.Therefore, the two vegetables, either as a fresh or sticky sauce, require additional sources of P, K, Na, Mg, Ca, Mn, and Zn to meet recommended dietary allowance. Furthermore, dried mucilagesauce, though, could be an appreciable post harvest management and storage but not without a loss of about one-third mineral content in the process. However, the sauce of common okra andbush okra are good sources for any of the assessed mineral restricted diets.

  7. Biology of flowering and nectar production in the flowers of the beauty bush (Kolkwitzia amabilis Graebn.

    Directory of Open Access Journals (Sweden)

    Marta Dmitruk

    2012-12-01

    Full Text Available Nectar production and the morphology of the nectary and pollen grains of Kolwitzia amabilis Graebn. were studied during the period 2008–2009 and in 2011. The blooming of beauty bush flowers started in the third decade of May and ended in the middle of June; flowering lasted 22–23 days. The flower life span was 4–5 days. Nectar production began at the bud break stage. The tube of the corolla in beauty bush flowers forms a spur inside which the nectary is located. The secretory surface of the nectary consists of two layers of glandular epidermal outgrowths: unicellular trichomes, with their length ranging 54.6 μm – 70.2 μm, and papillae with a length of 13.0 μm – 20.6 μm. The mean weight of nectar per 10 flowers, determined for the three years of the study, was 8.6 mg, with a sugar concentration of 50.8%. The weight of nectar sugar was on average 4.4 mg. In terms of the size, beauty bush pollen grains are classified as medium-sized. These are tricolporate grains.

  8. Research of on-line monitoring method for insulation condition of power transformer bushing

    Science.gov (United States)

    Xia, Jiuyun; Qian, Zheng; Yu, Hao; Yao, Junda

    2016-01-01

    The power transformer is the key equipment of the power system; its insulation condition will directly influence the security and reliability of the power system. Thus, the on-line monitoring of power transformer is urgently required in order to guarantee the normal operation of the power system. Moreover, the dielectric loss factor is a significant parameter reflecting the condition of transformer bushing, so the on-line measurement of dielectric loss factor is really important. In this paper, the phase-to-phase comparison method is selected as the on-line monitoring method based on the overall analysis and discussion of the existing on-line monitoring methods. At first, the harmonic analysis method is utilized to calculate the dielectric loss of each phase of the three-phase transformer bushing, and then the differences of dielectric loss between every two phases are calculated and analyzed. So the insulation condition of each bushing could be achieved based on the careful analysis of different phase-to-phase dielectric loss. The simulation results of phase-to-phase comparison method are carried out in this paper, and the validity is verified. At last, this method is utilized in an actual equipment of on-line monitoring.

  9. Wall Art

    Science.gov (United States)

    McGinley, Connie Q.

    2004-01-01

    The author of this article, an art teacher at Monarch High School in Louisville, Colorado, describes how her experience teaching in a new school presented an exciting visual challenge for an art teacher--monotonous brick walls just waiting for decoration. This school experienced only minimal instances of graffiti, but as an art teacher, she did…

  10. Bush animal attacks: management of complex injuries in a resource-limited setting

    Directory of Open Access Journals (Sweden)

    Mitchell Katrina B

    2011-12-01

    Full Text Available Abstract Introduction Though animal-related injuries and fatalities have been documented throughout the world, the variety of attacks by wild animals native to rural East Africa are less commonly described. Given the proximity of our northwestern Tanzania hospital to Lake Victoria, Lake Tanganyika, and the Serengeti National Park, and presentation of several patients attacked by bush animals and suffering a variety of complex injuries, we sought to report the pattern of attacks and surgical management in a resource-limited setting. Materials and methods Four patients who were admitted to the northwestern Tanzania tertiary referral hospital, Bugando Medical Centre (BMC, in 2010-2011 suffered attacks by different bush animals: hyena, elephant, crocodile, and vervet monkey. These patients were triaged as trauma patients in the Casualty Ward, then admitted for inpatient monitoring and treatment. Their outcomes were followed to discharge. Results The age and gender of the patients attacked was variable, though all but the pediatric patient were participating in food gathering or guarding activities in rural locations at the time of the attacks. All patients required surgical management of their injuries, which included debridement and closure of wounds, chest tube insertion, amputation, and external fixation of an extremity fracture. All patients survived and were discharged home. Discussion Though human injuries secondary to encounters with undomesticated animals such as cows, moose, and camel are reported, they often are indirect traumas resulting from road traffic collisions. Snake attacks are well documented and common. However, this series of unique bush animal attacks describes the initial and surgical management of human injuries in the resource-limited setting of the developing world. Conclusion Animal attacks are common throughout the world, but their pattern may vary in Africa throughout jungle and bush environmental settings. It is

  11. Improved dynamic phasor model of HVDC%高压直流输电动态相量模型的改进

    Institute of Scientific and Technical Information of China (English)

    孙慧平; 王西田; 李秀君

    2013-01-01

      动态相量已经被引入到HVDC建模中,其用开关函数来表示阀的开关状态,具有较好的精度。基于HVDC次同步振荡分析的需要,考虑晶闸管的死区特性和触发方式的影响,对HVDC的动态相量模型提出了改进,并在电磁暂态仿真平台上建立了改进后的HVDC动态相量模型。然后基于HVDC的基准系统,在统一的电磁暂态仿真平台下与HVDC的电磁暂态模型进行了仿真比较,对比不同频率扰动下交直流系统相关状态变量的时间响应曲线,较为严谨地验证了改进的HVDC动态相量模型在不同频段的适用性。%Dynamic phasors have been introduced to the HVDC model to analyze its dynamic behavior. Dynamic phasor method shows high accuracy by representing the switch state of the valve with switching function. In the need of HVDC sub-synchronization oscillation analysis, we consider the influence of thyristor dead time and trigger control on the HVDC dynamic phasor model, and accordingly establish an improved HVDC dynamic phasor model based on the electromagnetic transient simulation platform. Based on the baseline system of HVDC, we make a simulation comparison between PSCAD custom model and the electro transient model, comparing the time response curve of state variables between AC and DC system with disturbance of different frequency. Consequently, we authenticate the applicability of the improved HVDC dynamic phasor model in different frequency ranges.

  12. Analysis of MMC-HVDC Transient Response Characteristic Under Typical Disturbances%MMC-HVDC典型扰动暂态响应特性分析

    Institute of Scientific and Technical Information of China (English)

    马雅青; 王卫安; 张杰; 唐剑钊; 任涛

    2011-01-01

    为揭示具有新型拓扑结构的基于模块化多电平换流器直流输电系统MMC-HVDC(modular multilevel converter high voltage direct current)的电磁暂态特性,对该系统进行典型扰动暂态响应的特性分析根据MMC拓扑结构,推导了交流电网不平衡时的MMC交流侧电磁暂态模型,并基于模型设计了正、负序双内环电流控制和外环功率控制的控制策略.同时,对MMC-HVDC在各种典型扰动下的暂态响应特性进行了详细的仿真分析,仿真结果表明所设计的控制策略的正确性.MMC-HVDC在遭受各种典型扰动时具有良好的暂态响应特性,并能稳定、充裕地运行.%In order to reveal the electromagnetic transient characteristics of new topology structure MMC HVDC.it is necessary to study the transient response characteristics of the new HVDC under various typical disturbances. According to the topology structure of MMCthe electromagnetic transient model of AC side of MMC was derived under the condition of unbalance AC grid. The control strategies with inneer loops current control of positive and negative sequence and an outer loop's power control were designed. With various typical disturbances simulations,the transient response of MMC-HVDC was designed. With various typical disturb ances simulations,the transient response of MMC-HVDC was studied and the correctness of the proposed con trol strategy was confirmed. MMC-HVDC has good transient response characteristics, and can operate stably and fully under various typical disturbances.

  13. 一种MMC-HVDC的直流电压波动抑制新方法%A New Approach for Suppressing DC Voltage Ripples of MMC-HVDC

    Institute of Scientific and Technical Information of China (English)

    周月宾; 江道灼; 胡鹏飞; 梁一桥; 郭捷; 林志勇

    2013-01-01

    针对柔性直流输电系统常规直流电压波动抑制算法中存在的缺陷,提出一种适用于模块化多电平换流器型高压直流输电系统(modular multilevel converter based high voltage direct current,MMC-HVDC)的直流电压波动抑制方法。该方法利用MMC特有的“储能”特性,在交流系统不对称时,控制 MMC 交、直流侧瞬时有功功率不再平衡,从而实现MMC交流侧电流依然保持对称运行,同时直流侧电压、电流和功率保持为恒定。为了实现上述控制功能与目标,建立三相交流系统不对称时 MMC 直流回路的模型,设计αβ0坐标系下以比例谐振调节器为基础的控制策略,且探讨MMC-HVDC中的协调控制问题。最后,搭建71电平背靠背 MMC-HVDC 系统模型进行数字仿真,结果验证了所提控制方法的有效性。%Since the common solution for eliminating DC voltage ripples in voltage sourced converter based high voltage direct current (VSC-HVDC) transmission system has some drawbacks, this paper proposed a new method applied to modular multilevel converter based high voltage direct current (MMC-HVDC). The method uses the sub-module energy storage capability in MMC, making the instantaneous active power between ac and dc side of MMC unequal under unbalanced AC system. Meanwhile, this method keeps the ac current balanced, and eliminates the DC voltage, DC current and DC power ripples as well. To fulfill such a control goal, according to the dc-loop model of MMC, a controller inαβ0 frame based on proportional resonant regulator was designed, and then the coordinated control strategy was discussed in case of MMC-HVDC. Finally, a back-to-back MMC-HVDC simulation model with 71 levels was built to verify the proposed controller. The results show that the controller works well under both balanced and unbalanced AC system.

  14. HVDC在电网发展中的应用评“灵活电力传输-HVDC的选择”一书%HVDC Applications in Power Development——Book Review on Flexible Power Transmission: The HVDC Options

    Institute of Scientific and Technical Information of China (English)

    马长林; 唐寅生

    2011-01-01

    新书“灵活电力传输-HVDC的选择”,介绍了基于AC-DC的静止换流器及高压直流输电技术,涉及的内容主要是以最新的电力电子技术改造传统的以电网换相换流( LCC)或电流源换流(CSC)为基础的高压直流(HVDC)输电系统,并对以电压源换流(VSC)为基础的柔性直流VSC-HVDC技术做了较全面的论述.评述了作者全局意译的背景与内容介绍,并以实例为佐证论述灵活电力传输HVDC在电网发展中广阔的应用前景.

  15. CLIMBING WALL

    CERN Multimedia

    1999-01-01

    The FIRE AND RESCUE Group of TIS Commission informs that the climbing wall in the yard of the Fire-fighters Station, is intended for the sole use of the members of that service, and recalls that access to this installation is forbidden for safety reasons to all persons not belonging to the Service.CERN accepts no liability for damage or injury suffered as a result of failure to comply with this interdiction.TIS/DI

  16. Increase in fault ride through capability of direct drive permanent magnet based wind farm using VSC-HVDC

    Science.gov (United States)

    Maleki, Hesamaldin; Ramachandaramurthy, V. K.; Lak, Moein

    2013-06-01

    Burning of fossil fuels and green house gasses causes global warming. This has led to governments to explore the use of green energies instead of fossil fuels. The availability of wind has made wind technology a viable alternative for generating electrical power. Hence, many parts of the world, especially Europe are experiencing a growth in wind farms. However, by increasing the number of wind farms connected to the grid, power quality and voltage stability of grid becomes a matter of concern. In this paper, VSC-HVDC control strategy which enables the wind farm to ride-through faults and regulate voltage for fault types is proposed. The results show that the wind turbine output voltage fulfills the E.ON grid code requirements, when subjected to three phase to ground fault. Hence, continues operation of the wind farm is achieved.

  17. Optimal dynamic capacity allocation of HVDC interconnections for cross-border exchange of balancing services in presence of uncertainty

    DEFF Research Database (Denmark)

    Delikaraoglou, Stefanos; Pinson, Pierre; Eriksson, Robert

    2015-01-01

    of the power system depends both on the technical parameters of its components, i.e., generators and transmission infrastructure, as well as on the operational practices that make optimal use of the available assets. This work focuses on alternative market designs that enable sharing of cross-border balancing...... and the uncertainty arising from their partial predictability. Considering that the existing setup of the European electricity markets promotes the spatial coordination of neighbouring power systems only on the day-ahead market stage, regional system operators have to rely mainly on their internal balancing resources...... resources between adjacent power systems through High Voltage Direct Current (HVDC) interconnections which provide increased controllability. In this context, we formulate a stochastic market-clearing algorithm that attains full spatio-temporal integration of reserve capacity, day-ahead and balancing...

  18. Protection of ± 500 kV HVDC Double-circuit Converter Station from Lightning Induced Overvoltage

    Institute of Scientific and Technical Information of China (English)

    DONG Manling; YUAN Zhiyong; LI Tianwei; ZHAO Xiangen; ZHANG Jiaxin; HE Junjia

    2013-01-01

    In order to obtain reasonable schemes of arrester in converter stations,the arrester scheme of"Xiluodu-Guangdong HVDC ±500 kV double circuit transmission" project against lighting induced overvoltage,which was designed according to the main principle of lightning protection in converter station,is discussed.A calculation of the lighting induced overvoltage in Zhaotong converter station under various operation modes is performed with ATP-EMTP software,then the surge arrester configuration of the converter station is decided,and the arrester protection schemes of smoothing reactor and neutral line are studied.It is concluded that additional protection is necessary because of the relatively large gap between protected disconnecting switch and arrester of metallic return transfer bus.Plus,the smoothing reactor (SR) arrester near the valve hall could be removed to improve the scheme's economic performance.

  19. A Review of Muti-Terminal VSC-HVDC System in Large Wind Farms%大型风电基地多端 VSC-HVDC系统综述

    Institute of Scientific and Technical Information of China (English)

    吴瀚俊; 刘海涛

    2014-01-01

    In recent years,the upgrowth of fully-controlled devices and pulse width modulation device PWM technology,has paved the way for the appearance and progression of VSC-HVDC technology.Multi-terminal VSC-HVDC technology can be applied to address such problems as island supply,distributed generation system connecting to large power grids,etc.This paper elucidates the principle of VSC-HVDC,and compares AC transmission and normal HVDC,aimed at highlighting the advantages of VSC-HVDC.The working mode of convertors,a key part of VSC-HVDC,is also briefly introduced.More importantly,this paper demonstrates topology and coordination control strategy of multi-terminal VSC-HVDC system in large-scale offshore wind farms,and predicts its future development trend.%随着近年来全控型器件的出现和发展以及脉宽调制( PWM)技术的日臻成熟,为VSC-HVDC技术的产生和发展创造了条件,而多端VSC-HVDC技术可以很好地解决孤岛供电、分布式发电系统接入大电网等问题。文章就VSC-HVDC原理进行阐述,通过对比交流输电和常规HVDC来突出VSC-HVDC的优点,并简单介绍了VSC-HVDC的关键部分也就是变流器的运行模式。文章重点论述大型风电基地多端VSC-HVDC系统的拓扑结构和协调控制策略,并对其未来发展趋势作出预测。

  20. Analysis on Harmonic Instability in HVDC Transmission System%高压直流输电系统谐波失稳的分析

    Institute of Scientific and Technical Information of China (English)

    彭晨光; 褚优群; 马秀林

    2015-01-01

    针对HVDC(高压直流输电系统)存在的谐波失稳问题,通过计算电网动态过程中直流线路向整流、逆变两侧的等效阻抗,指出HVDC交直流两侧特定谐波的等效阻抗是研究谐波放大失稳的关键。根据PSCAD/EMTDC仿真软件中的HVDC电磁暂态模型,针对不同工况模拟计算。仿真结果表明,换流变铁心饱和导致了HVDC基频等效阻抗的实部减小甚至为负值,使其应对扰动的阻尼效果减小从而可能诱发HVDC谐波振荡失稳。%Aiming at harmonic instability in HVDC (high-voltage direct current) transmission system, the pa-per calculates equivalent impedance seen from the DC line to both converter and inverter sides in the power system transient state and indicates that equivalent impedance of particular harmonic at AC side and DC side of HVDC is the key of harmonic amplification instability research. Simulation and calculation is carried out in different operating conditions by use of HVDC electromagnetic transient model in PSCAD/EMTDC software. The simulation shows that the core saturation of the converter transformer leads to decrease or even negative value of real part of the converter DC side fundamental equivalent impedance, resulting further instability and oscillation in the system because of the damping reduction.

  1. Rose bush leaf and internode expansion dynamics: analysis and development of a model capturing interplant variability

    Directory of Open Access Journals (Sweden)

    Sabine eDemotes-Mainard

    2013-10-01

    Full Text Available Bush rose architecture, among other factors, such as plant health, determines plant visual quality. The commercial product is the individual plant and interplant variability may be high within a crop. Thus, both mean plant architecture and interplant variability should be studied. Expansion is an important feature of architecture, but it has been little studied at the level of individual organs in bush roses. We investigated the expansion kinetics of primary shoot organs, to develop a model reproducing the organ expansion of real crops from non destructive input variables. We took interplant variability in expansion kinetics and the model’s ability to simulate this variability into account. Changes in leaflet and internode dimensions over thermal time were recorded for primary shoot expansion, on 83 plants from three crops grown in different climatic conditions and densities. An empirical model was developed, to reproduce organ expansion kinetics for individual plants of a real crop of bush rose primary shoots. Leaflet or internode length was simulated as a logistic function of thermal time. The model was evaluated by cross-validation. We found that differences in leaflet or internode expansion kinetics between phytomer positions and between plants at a given phytomer position were due mostly to large differences in time of organ expansion and expansion rate, rather than differences in expansion duration. Thus, in the model, the parameters linked to expansion duration were predicted by values common to all plants, whereas variability in final size and organ expansion time was captured by input data. The model accurately simulated leaflet and internode expansion for individual plants (RMSEP = 7.3% and 10.2% of final length, respectively. Thus, this study defines the measurements required to simulate expansion and provides the first model simulating organ expansion in rosebush to capture interplant variability.

  2. Biomonitoring of chemical elements in an urban environment using arboreal and bush plant species.

    Science.gov (United States)

    Rucandio, Maria Isabel; Petit-Domínguez, Maria Dolores; Fidalgo-Hijano, Concepcion; García-Giménez, Rosario

    2011-01-01

    The aim of this work was to investigate the possibility of using several bush and arboreal plant species, usually present as ornamental plants in street and parks, as environmental indicators of pollution. This is a research paper that evaluates the real possibility of using a fast and low-cost procedure to evaluate the pollution degree through data obtained from plant species growing within an urban environment. Leaves of six different bush and arboreal species were collected from different parts of Madrid (Spain), ranging from highly polluted considered areas to medium and low contaminated ones. A total of 66 chemical elements, from major to minor and trace, were determined for every leaf sample by inductively coupled plasma-mass spectrometry. Statistical analyses were carried out using mainly box and whisker plots, linear discriminant analysis and cluster analysis. The pollution by different elements of the studied areas of Madrid cannot be considered generally dangerous for human health. The level detected for the contaminants, in general, is similar or lower than other urban cities. Pb and V concentrations in plant samples tend to increase as traffic density increases. The different studied plant species showed a different capability of accumulation of certain elements. Cedrus deodara accumulates specially Ag, Hg, Mo and V; Cupressus sempervirens, Zr; Pinus pinea, As and Sb; Nerium oleander Ni, Pb, Mo and Se; Ligustrum ovalifolium, Sc and V; and Pittosporum tobira, Ag, Cd, Rb and Sc. The leaves and needles collected from bush and arboreal plants common in this city have demonstrated to be useful to evaluate the level of pollution not only through the chemical analysis but also through the recognition of the visual injury symptoms. The application of multivariate statistical techniques combined with determining of element concentration and correlation analysis has been proved to be an effective tool for reach the objectives of the present work. This allows

  3. La ciencia como solución sin límites. El informe Bush (1945)

    OpenAIRE

    Pérez-López, P. (Pablo)

    2012-01-01

    En 1945, Vannevar Bush, que había drigido el Offtce of Scientijic Research and Development por encargo del gobierno norteamericano durante la Segunda Guerra Mundial, contestó a la pregunta del Presidente Roosevelt sobre el papel que la ciencia debía desempeñar en el tiempo de paz. Analizamos su respuesta para acercarnos a la historia de la idea de progreso científico, económico y social en esos años y a su relación o ausencia de relación con aspectos éticos de la vida humana.

  4. Control of the bush tick (Haemaphysalis longicornis) with Zebu x European cattle.

    Science.gov (United States)

    Dicker, R W; Sutherst, R W

    1981-02-01

    Brahman x Hereford cattle carried only one-quarter as many engorging adult bush ticks (Haemaphysalis (Kaiseriana) longicornis) as Hereford. Simmental x Hereford or Friesian x Hereford cattle when grazed together on the north coast of New South Wales. Fourteen percent of a Brahman x Hereford herd carried half of the engorging ticks suggesting that infestation levels would be further reduced by culling procedures. The results indicate an additional advantage to those already established for Brahman x Hereford cattle on the north coast of New South Wales and have important implications for tick control.

  5. Modelling of the carburizing and quenching process applied to caterpillar track bushings

    Science.gov (United States)

    Ferro, P.; Bonollo, F.

    2014-03-01

    The carburizing-quenching process applied to caterpillar track bushings was studied by means of experimental and numerical analyses. The numerical model was developed on the basis of the real cycle. The purpose of this work is to predict the carbon profiles, microstructural phase changes, hardness and residual stress that occur during quenching using finite element techniques. Good agreement was obtained between the experimental and numerical results in terms of carbon diffusion and hardness profiles. The Sysweld® numerical code was used to perform the simulations.

  6. Oversimplifying Iraq's challenges: Bush's Fort Bragg speech and americans' declining support for the war

    Directory of Open Access Journals (Sweden)

    Carlos L. Yordan

    2009-11-01

    Full Text Available Este artículo examina el porqué el presidente George W. Bush no pudo recolectar la ayuda de la ciudadanía americana para su estrategia para la estabilización y la transformación de Iraq. De hecho, esta estrategia ha sido afectada por el desplegar de los acontecimientos que sucedieron en Iraq, pero el problema principal reside en las posiciones que el presidente utilizó para simplificar los desafíos que el ejército americano y la diplomacia tenían que hacer frente en Iraq, buscando la aprobación de las criticas periodisticas, de los expertos gubernamentales y de los juristas. En más de una perspectiva la falta de aprobación del gobierno Bush en Iraq es una consecuencia de la carencia de la confianza que la opinión pública tuvo por su presidente y sus consejeros para lograr sus objetivos en Iraq. Para constatar esta tesis, el artículo analiza el discurso del presidente a la nación, difundida en horario de punta el 28 de julio de 2005, que demuestra que los americanos no estaban demasiado convencidos de la estrategia de Bush._____________ABSTRACT:This article puts in context why President of the United States of America George W. Bush has been unable to rally American support for his strategy to stabilize and transform Iraq. Since the summer of 2003, when Iraqis started to challenge the authority of the Anglo-American occupation, the White House has been on the defensive, while American support for post-war efforts has dwindled. While developments in Iraq have affected the strategy’s execution, the main problem is the president’s inclination to oversimplify the challenges American troops and diplomats are facing in Iraq, inviting criticism from journalists, experts on nation-building and lawmakers. In many ways, declining approval of Bush’s handling of Iraq results in the public’s lack of confidence that the president and his advisors will be able to accomplish its goals in Iraq. To test this argument, the article analyzes

  7. Bush aide blocked report: global health draft in 2006 rejected for not being political.

    Science.gov (United States)

    Lee, Christopher; Kaufman, Marc

    2008-01-01

    A surgeon general's report in 2006 that called on Americans to help tackle global health problems has been kept from the public by a Bush political appointee without any background or expertise in medicine or public health, chiefly because the report did not promote the administration's policy accomplishments. The report described the link between poverty and poor health, urged the U.S. government to help combat widespread diseases as a key aim of its foreign policy, and called on corporations to help improve health conditions in the countries where they operate.

  8. 模块化多电平变流器HVDC输电系统控制策略%Control Strategy of Modular Multilevel Converters Based HVDC Transmission

    Institute of Scientific and Technical Information of China (English)

    赵岩; 胡学浩; 汤广福; 贺之渊

    2011-01-01

    This paper built an electromagnetic transient mathematical model of modular multilevel converters (MMCs) and dynamic model of DC voltage in high voltage direct current (HVDC) transmission that adopts MMC as converter. Based on it, the dynamic characteristic of DC voltage in HVDC transmission was analyzed, and HVDC control system parameters coordinated design principles and its algorithm were proposed. Finally, the correctness of proposed submodule capacitor voltage balancing scheme, MMC based HVDC control system parameters coordinated design principles and its algorithm were verified by digital simulation based on PSCAD/EMTDC.%建立模块化多电平变流器(modular multilevel converters,MMCl的电磁暂态数学模型以及采用MMC为变流器的高压直流输电系统(high voltage direct current,HVDC)直流侧电压的动态数学模型。在此基础上,分析HVDC系统的直流侧电压动态特性,给出HVDC控制器参数协调设计原则和算法。最后,基于PscAD/EMTDc的数字仿真结果证明了所提出的HVDC控制系统参数协调设计原则和算法的正确性。

  9. Examination of fault ride-through methods for off-shore wind farms connected to the grid through VSC-based HVDC transmission

    Energy Technology Data Exchange (ETDEWEB)

    Karaagac, U.; Mahseredjian, J.; Saad, H. [Ecole Polytechnique de Montreal, QC (Canada); Jensen, S.; Cai, L. [REpower Systems AG, Hamburg (Germany)

    2012-07-01

    The fault ride-through (FRT) performance of offshore wind farms (OWFs) is a challenging task when the OWF is connected to the onshore ac grid through a voltage source converter (VSC) based HVDC transmission system. The injected power from the OWF cannot be reduced by the offshore VSC during onshore ac faults and this causes a fast increase in the dc network voltage. Without any special FRT method, the dc network voltage may increase up to intolerable levels and cause operation of dc overvoltage protection. This paper compares various FRT methods based on fast reduction of power generation in OWFs. In addition, this paper proposes an improved FRT method based on controlled voltage drop for output power reduction in OWFs. The proposed improvement reduces mechanical stress on the wind turbine (WT) drive train, and electrical stress on the insulated gate bipolar transistors (IGBTs) of the HVDC and doubly-fed induction generator (DFIG) converters. Practical onshore ac fault scenarios are simulated for an OWF composed of DFIG type WTs and connected to a practical ac grid through a point-to-point modular multilevel converter (MMC) based HVDC system. (orig.)

  10. A política comercial da administração Bush: o CAFTA-DR e a resistência interior Bush's trade policy: the CAFTA-DR and the inner resistence

    Directory of Open Access Journals (Sweden)

    Thiago Lima

    2009-06-01

    Full Text Available Argumenta-se que a política comercial da administração Bush é uma importante modificação na tradição norte-americana ao aderir à proliferação de acordos bilaterais. Contudo, a análise do CAFTA-DR demonstra que ela pode encontrar forte resistência doméstica.It is argued that the Bush Administration's trade policy is an important change in the U.S. tradition because of the proliferation of bilateral agreements. However, the analysis of the CAFTA-DR demonstrates that it can found strong domestic resistance.

  11. Neotropical Zoonotic Parasites in Bush Dogs (Speothos venaticus) from Upper Paraná Atlantic Forests in Misiones, Argentina.

    Science.gov (United States)

    Vizcaychipi, Katherina A; Rinas, Miguel; Irazu, Lucia; Miyagi, Adriana; Argüelles, Carina F; DeMatteo, Karen E

    2016-10-01

    Wildlife remains an important source of zoonotic diseases for the most vulnerable groups of humans, primarily those living in rural areas or coexisting with forest. The Upper Paraná Atlantic forest of Misiones, Argentina is facing ongoing environmental and anthropogenic changes, which affect the local biodiversity, including the bush dog (Speothos venaticus), a small canid considered Near Threatened globally and Endangered locally. This project aimed to expand the knowledge of zoonotic parasites present in the bush dog and the potential implications for human health and conservation medicine. From May to August 2011, a detection dog located 34 scats that were genetically confirmed as bush dog and georeferenced to northern Misiones. Of these 34 scats, 27 had sufficient quantity that allowed processing for zoonotic parasites using morphological (sedimentation and flotation) and antigen (coproantigen technique) analyses. Within these 27 scats, we determined that the parasitic prevalence was 63.0% (n = 17) with 8 (47.1%) having mixed infections with 2-4 parasitic genera. No significant differences (p > 0.05) between sampling areas, sex, and parasite taxa were found. We were able to summarize the predominant nematodes (Ancylostoma caninum, Toxocara canis, and Lagochilascaris spp.), cestodes (Taenia spp. and Spirometra spp.), and apicomplexa (Cystoisospora caninum) found in these bush dogs. With the copro-ELISA technique, 14.8% (n = 4) of the samples were positive for Echinococcus spp. This study represents the first comprehensive study about parasitic fauna with zoonotic potential in the free-ranging bush dog. This information combined with the innovative set of techniques used to collect the samples constitute a valuable contribution that can be used in control programs, surveillance of zoonotic diseases, and wildlife conservation, both regionally and across the bush dog's broad distribution.

  12. Ilves ja Bush - üks rantšopidajast president kutsus teise külla / Krister Paris

    Index Scriptorium Estoniae

    Paris, Krister

    2007-01-01

    USA presidendi George W. Bushi kohtumisest president Toomas Hendrik Ilvesega. Kõne all oli viisavabadus ja NATO küberkaitsekeskuse loomine Eestisse. G.W. Bush avaldas kaastunnet Afganistanis hukkunud Eesti sõdurite omastele. Riigikogu liikmete Marko Mihkelsoni ja Sven Mikseri kommentaarid presidentide kohtumisele. Vt. samas: Esimene riigipea pärjaga. T.H. Ilves asetas pärja kommunismiohvrite mälestusmärgile, mille president G.W. Bush avas 12. juunil 2007. Vabariigi President töövisiidil Ameerika Ühendriikides 25.-26.06.2007

  13. Ilves ja Bush - üks rantšopidajast president kutsus teise külla / Krister Paris

    Index Scriptorium Estoniae

    Paris, Krister

    2007-01-01

    USA presidendi George W. Bushi kohtumisest president Toomas Hendrik Ilvesega. Kõne all oli viisavabadus ja NATO küberkaitsekeskuse loomine Eestisse. G.W. Bush avaldas kaastunnet Afganistanis hukkunud Eesti sõdurite omastele. Riigikogu liikmete Marko Mihkelsoni ja Sven Mikseri kommentaarid presidentide kohtumisele. Vt. samas: Esimene riigipea pärjaga. T.H. Ilves asetas pärja kommunismiohvrite mälestusmärgile, mille president G.W. Bush avas 12. juunil 2007. Vabariigi President töövisiidil Ameerika Ühendriikides 25.-26.06.2007

  14. Molecular cloning and expression of a bush related CmV1 gene in tropical pumpkin.

    Science.gov (United States)

    Wu, Tao; Cao, Jiashu

    2010-02-01

    A bush-type plant was selected from tropical pumpkin 'cga' (Cucurbita moschata Duchesne) in order to study the vine development in C. moschata. In this study, a novel gene encoding NADH dehydrogenase was isolated from the vine line (cgaV) of C. moschata, that was not expressed in the near isogenic bush line (cgaBu). This gene, designated as CmV1 (C. moschata vine 1), was 545 bp in length and was composed of a 477 bp open reading frame, which had 99% nucleotide similarity to the chloroplast ndhJ gene for NADH dehydrogenase subunit J from Brassica oleracea. The deduced amino acid sequence of CmV1 had 99% similarity to NADH dehydrogenase subunit J from Arabidopsis and had 98% similarity to NADH dehydrogenase subunit from Barbarea verna. Analysis of the basic characteristics of the CmV1 protein revealed that it has one Respiratory chain NADH dehydrogenase 30 kD subunit signature, three N-myristoylation sites, one Casein kinase II phosphorylation site, and one Protein kinase C phosphorylation site. Reverse transcriptase-PCR analysis showed that CmV1 was expressed at a high level in the internodes and hypocotyls and was expressed stronger in elongating internodes than in fully expanded internodes. In conclusion, results obtained in the present study suggest that CmV1 gene might play important roles in vine elongation of tropical pumpkin.

  15. Fluid technologies: The Bush Pump, the LifeStraw and microworlds of humanitarian design.

    Science.gov (United States)

    Redfield, Peter

    2016-04-01

    Over the past decade, many ingenious, small-scale gadgets have appeared in response to problems of disaster and extreme poverty. Focusing on the LifeStraw, a water filtration device invented by the company Vestergaard Frandsen, I situate this wave of humanitarian design relative to Marianne de Laet and Annemarie Mol's classic article on the Zimbabwe Bush Pump. The LifeStraw shares the Bush Pump's principle of technical minimalism, as well as its ethical desire to improve the lives of communities. Unlike the pump, however, the straw defines itself through rather than against market logic, accepting the premise that one can 'do well while doing good'. Moreover, it does not share the assumed framework of de Laet and Mol's Zimbabwean socio-technical landscape: a postcolonial state happily en route to national self-definition. Nonetheless, it clearly embodies moral affect, if in the idiom of humanitarian concern rather than development. My aim is to open up three interrelated lines of inquiry for discussion. First, I consider aspects of a postcolonial condition at the micro-level of immediate needs, including assumptions about nation-state politics and markets. Second, I emphasize science and technology in the form of infrastructure, the material frontline of norms. Third, I return reflexively to love, and the complicated allure of engagement in academic work.

  16. Glaciations, gradients, and geography: multiple drivers of diversification of bush frogs in the Western Ghats Escarpment.

    Science.gov (United States)

    Vijayakumar, S P; Menezes, Riya C; Jayarajan, Aditi; Shanker, Kartik

    2016-08-17

    The historical processes underlying high diversity in tropical biodiversity hotspots like the Western Ghats of Peninsular India remain poorly understood. We sampled bush frogs on 13 massifs across the Western Ghats Escarpment and examined the relative influence of Quaternary glaciations, ecological gradients and geological processes on the spatial patterns of lineage and clade diversification. The results reveal a large in situ radiation (more than 60 lineages), exhibiting geographical structure and clade-level endemism, with two deeply divergent sister clades, North and South, highlighting the biogeographic significance of an ancient valley, the Palghat Gap. A majority of the bush frog sister lineages were isolated on adjacent massifs, and signatures of range stasis provide support for the dominance of geological processes in allopatric speciation. In situ diversification events within the montane zones (more than 1800 m) of the two highest massifs suggest a role for climate-mediated forest-grassland persistence. Independent transitions along elevational gradients among sub-clades during the Miocene point to diversification along the elevational gradient. The study highlights the evolutionary significance of massifs in the Western Ghats with the high elevations acting as centres of lineage diversification and the low- and mid-elevations of the southern regions, with deeply divergent lineages, serving as museums.

  17. MARIOLA: A model for calculating the response of mediterranean bush ecosystem to climatic variations

    Energy Technology Data Exchange (ETDEWEB)

    Uso-Domenech, J.L.; Ramo, M.P. [Department of Mathematics, Campus de Penyeta Roja, University Jaume I, Castellon (Spain); Villacampa-Esteve, Y. [Department of Analysis and Applied Mathematics, University of Alicante (Spain); Stuebing-Martinez, G. [Department of Botany, University of Valencia (Spain); Karjalainen, T. [Faculty of Forestry, University of Joensuu (Finland)

    1995-07-01

    The paper summarizes the bush ecosystem model developed for assessing the effects of climatic change on the behaviour of mediterranean bushes assuming that temperature, humidity and rain-fall are the basic dimensions of the niche occupied by shrub species. In this context, changes in the monthly weather pattern serve only to outline the growth conditions due to the nonlinearity of response of shrubs to climatic factors. The plant-soil-atmosphere system is described by means of ordinary non-linear differential equations for the state variables: green biomass, woody biomass, the residues of green and woody biomasses, faecal detritus of mammals on the soil, and the total organic matter of the soil. The behaviour of the flow variables is described by means of equations obtained from non-linear multiple regressions from the state variables and the input variables. The model has been applied with success to the behaviour of Cistus albidus in two zones of the Province of Alicante (Spain). The data base for the parametrical locations (zone 1) and validation (zone 2) is based upon measurements taken weekly over a 2-year period. The model is used to simulate the response of this shrub to a decreasing tendency in precipitation combined with a simultaneous rise in temperature. A period of 10 years is simulated and it is observed that plants with woody biomass smaller than 85 g die between the first and the third month and other plants` biomass decreases during this period, and strongly thereafter

  18. Heterogeneous WSx/WO₃ Thorn-Bush Nanofiber Electrodes for Sodium-Ion Batteries.

    Science.gov (United States)

    Ryu, Won-Hee; Wilson, Hope; Sohn, Sungwoo; Li, Jinyang; Tong, Xiao; Shaulsky, Evyatar; Schroers, Jan; Elimelech, Menachem; Taylor, André D

    2016-03-22

    Heterogeneous electrode materials with hierarchical architectures promise to enable considerable improvement in future energy storage devices. In this study, we report on a tailored synthetic strategy used to create heterogeneous tungsten sulfide/oxide core-shell nanofiber materials with vertically and randomly aligned thorn-bush features, and we evaluate them as potential anode materials for high-performance Na-ion batteries. The WSx (2 ≤ x ≤ 3, amorphous WS3 and crystalline WS2) nanofiber is successfully prepared by electrospinning and subsequent calcination in a reducing atmosphere. To prevent capacity degradation of the WSx anodes originating from sulfur dissolution, a facile post-thermal treatment in air is applied to form an oxide passivation surface. Interestingly, WO3 thorn bundles are randomly grown on the nanofiber stem, resulting from the surface conversion. We elucidate the evolving morphological and structural features of the nanofibers during post-thermal treatment. The heterogeneous thorn-bush nanofiber electrodes deliver a high second discharge capacity of 791 mAh g(-1) and improved cycle performance for 100 cycles compared to the pristine WSx nanofiber. We show that this hierarchical design is effective in reducing sulfur dissolution, as shown by cycling analysis with counter Na electrodes.

  19. Development and validation of the Bush-Francis Catatonia Rating Scale – Brazilian version

    Directory of Open Access Journals (Sweden)

    Ana Letícia Santos Nunes

    Full Text Available ABSTRACT Objective: This article aims to describe the adaptation and translation process of the Bush-Francis Catatonia Rating Scale (BFCRS and its reduced version, the Bush-Francis Catatonia Screening Instrument (BFCSI for Brazilian Portuguese, as well as its validation. Methods: Semantic equivalence processes included four steps: translation, back translation, evaluation of semantic equivalence and a pilot-study. Validation consisted of simultaneous applications of the instrument in Portuguese by two examiners in 30 catatonic and 30 non-catatonic patients. Results: Total scores averaged 20.07 for the complete scale and 7.80 for its reduced version among catatonic patients, compared with 0.47 and 0.20 among non-catatonic patients, respectively. Overall values of inter-rater reliability of the instruments were 0.97 for the BFCSI and 0.96 for the BFCRS. Conclusion: The scale's version in Portuguese proved to be valid and was able to distinguish between catatonic and non-catatonic patients. It was also reliable, with inter-evaluator reliability indexes as high as those of the original instrument.

  20. Environmental geophysics at the Southern Bush River Peninsula, Aberdeen Proving Ground, Maryland

    Energy Technology Data Exchange (ETDEWEB)

    Davies, B.E.; Miller, S.F.; McGinnis, L.D. [and others

    1995-05-01

    Geophysical studies have been conducted at five sites in the southern Bush River Peninsula in the Edgewood Area of Aberdeen Proving Ground, Maryland. The goals of the studies were to identify areas containing buried metallic objects and to provide diagnostic signatures of the hydrogeologic framework of the site. These studies indicate that, during the Pleistocene Epoch, alternating stands of high and low sea level resulted in a complex pattern of channel-fill deposits. Paleochannels of various sizes and orientations have been mapped throughout the study area by means of ground-penetrating radar and EM-31 techniques. The EM-31 paleochannel signatures are represented onshore either by conductivity highs or lows, depending on the depths and facies of the fill sequences. A companion study shows the features as conductivity highs where they extend offshore. This erosional and depositional system is environmentally significant because of the role it plays in the shallow groundwater flow regime beneath the site. Magnetic and electromagnetic anomalies outline surficial and buried debris throughout the areas surveyed. On the basis of geophysical measurements, large-scale (i.e., tens of feet) landfilling has not been found in the southern Bush River Peninsula, though smaller-scale dumping of metallic debris and/or munitions cannot be ruled out.

  1. 背靠背VSC-HVDC的多目标优化布点%Multi-Objective Optimal Allocation of Back-to-BackVSC-HVDC

    Institute of Scientific and Technical Information of China (English)

    关玉衡; 汪隆君; 王钢

    2016-01-01

    电网间的电气联系日趋紧密,多个500 kV变电站短路电流接近或超过断路器遮断容量,严重威胁电网安全。采用背靠背电压源换流器型高压直流输电(voltage source convertor-based high voltage direct current,VSC-HVDC)技术限制短路电流的方案获得业界的关注和认同。在分析VSC-HVDC 降低短路电流原理的基础上,建立以短路电流降低综合效果和投资经济性最优为目标的VSC-HVDC多目标优化布点模型,并采用快速非支配排序遗传算法求解;通过多端口网络等值模型约简可行解空间,以提高个体适应度评估速度;基于模糊选择策略获得最优折中分期建设方案。以2015年夏大运行方式的广东电网为算例,验证表明:1)短路电流降低综合效果指标能有效反映限流措施效果和作用范围;2)多端口网络等值能大幅提高算法求解效率;3)综合限流效果与配置点短路电流大小无直接关系。%Electrical connection between power grids becomes increasingly closer. Short-circuit currents of several 500kVsubstations approach or exceed breaking capability of circuit breakers, seriously threatening safe operation of power grid. Scheme of back-to-back voltage source convertor-based HVDC (VSC-HVDC) technology for short-circuit current limiting attracts more and more attention and gets recognition from power industry. Based on analyzing principle of using VSC-HVDC to reduce short-circuit current, multi-objective optimal allocation model of VSC-HVDC is established with objectives of optimizing comprehensive effects of reducing short-circuit current and investment economy. Non-dominated sorting genetic algorithm-II is employed to solve the proposed model. In order to improve speed of individual fitness evaluation, feasible solution space is reduced with multi-port network equivalent model. Fuzzy selection strategy is used to obtain optimal compromised phased construction scheme

  2. The USA policy evolution in the Caspian sea from Clinton to Bush; L'evolution de la politique americaine dans la region de la mer Caspienne de Clinton a Bush

    Energy Technology Data Exchange (ETDEWEB)

    Jafalian, A

    2003-07-01

    The author analyzes the USA policy in the Caspian Sea area and its evolution with the election of Bush. If no major orientation appear, some sensible evolutions are presented concerning the pipelines management in this area. The author presents then, the new definition of the economical variables and the reinforcement of the security dimension of the USA policy. (A.L.B.)

  3. Labor and the Bush Administration: “down so long, seem like up to me” Le syndicalisme américain pendant les années Bush

    Directory of Open Access Journals (Sweden)

    Gerald Friedman

    2010-03-01

    Full Text Available For a century, scholars and labor movement activists have debated the question of “American Exceptionalism,” or the distinctive nature of the labor movement in the United States. The weakness of American unions, especially their lack of members, has been attributed to distinctive features of American society, notably the hostility of the American government towards unions. Those who accept this Exceptionalist view have urged unions in the United States to become more active politically in order to strengthen their position. Since 1980, unions have followed this advice and have doubled their political spending. Most of the unions’ political activity and spending has been in support of candidates of the Democratic Party; but unions have received little in return from Democrats, even during the Clinton Administration. Indeed, during the administration of George W. Bush, union membership fell at almost exactly the same rate as before notwithstanding the Bush Administration’s open hostility towards unions and its attempt to use state power against unions in both the private and public sectors. In fact, over the last decades, we may be seeing the end of Exceptionalism. Since 1990, union membership decline has been slower in the United States than in most other OECD member states, despite a relatively hostile political and legal regime. Combined with the negligible effect of the Bush Administration on American unions, this suggests that union weakness in the United States is not due to exceptional features of the United States but to characteristics it shares with other countries. Throughout the affluent world, the idea of the labor movement has lost its tie to the broader democratic aspirations. In America and elsewhere, union revival depends on more than some incremental legal changes or political victories. It depends on the revival of the formative ideals of the labor movement, equality, fraternity, and the struggle for free and democratic

  4. Falling walls

    CERN Multimedia

    It was 20 years ago this week that the Berlin wall was opened for the first time since its construction began in 1961. Although the signs of a thaw had been in the air for some time, few predicted the speed of the change that would ensue. As members of the scientific community, we can take a moment to reflect on the role our field played in bringing East and West together. CERN’s collaboration with the East, primarily through links with the Joint Institute for Nuclear Research, JINR, in Dubna, Russia, is well documented. Less well known, however, is the role CERN played in bringing the scientists of East and West Germany together. As the Iron curtain was going up, particle physicists on both sides were already creating the conditions that would allow it to be torn down. Cold war historian Thomas Stange tells the story in his 2002 CERN Courier article. It was my privilege to be in Berlin on Monday, the anniversary of the wall’s opening, to take part in a conference entitled &lsquo...

  5. Study on Space Charge Characteristic of New XLPE Insulation Material for HVDC Cable%新型XLPE高压直流电缆绝缘料的空间电荷特性研究

    Institute of Scientific and Technical Information of China (English)

    陈曦; 吴锴

    2015-01-01

    The temperature gradient effect during operation of HVDC cables will lead to field distortion greatly of the outer insulation layer, which would lead to the electric strength and lifetime of cable insu-lation decrease. Based on the polyethylene nanocomposites, a new HVDC cable insulation material was prepared by adding crosslinking agent and antioxygen, and its mechanical properties and electrical proper-ties were tested, and then its space charge accumulation and field distortion characteristic were compared with foreign XLPE HVDC cable insulation material. The results show that the properties of the new HVDC cable insulation material are superior to the foreign cable material, and the new HVDC cable insu-lation material is expected to be used in the production of HVDC cables.%高压直流电缆运行中的温度梯度效应导致电缆外绝缘层场强严重畸变,降低了绝缘的电气强度和使用寿命。在聚乙烯纳米复合材料的基础上,添加适量的交联剂、抗氧剂等制备了新型高压直流交联聚乙烯料,对其力学性能和电性能进行测试,并将其与国外主流XLPE直流电缆绝缘料的空间电荷积聚与场强畸变特性进行对比分析。结果表明:新型高压直流交联聚乙烯电缆料的性能优于国外主流XLPE直流电缆绝缘料,有望用于国产高压直流电缆。

  6. Relações Brasil e Estados Unidos no período Bush: expectativas e frustrações

    Directory of Open Access Journals (Sweden)

    Virgílio Caixeta Arraes

    2012-09-01

    The article deals with the political and economic relationship between Brazil and United States during the George W Bush mandate (2001-2008. It  discusses the failed attempt to establish a hemispheric free trade agreement, due to the American protectionism, and to expand the use of biofuel. Finally, it also discusses the creation of the Fourth Fleet.

  7. President Bush : langenud nõuavad, et me jätkame võitlust! / Tõnis Erilaid

    Index Scriptorium Estoniae

    Erilaid, Tõnis, 1943-

    2005-01-01

    Salt Lake Citys USA sõjaveteranidele peetud kõnes ütles USA president George W. Bush, et tuleb jõuda eesmärgile, mille eest USA sõdurid oma elu andsid. Samas toimus sõjavastaste demonstratsioon

  8. Effects of organic fertilizers on the growth and yield of bush bean, winged bean and yard long bean

    Directory of Open Access Journals (Sweden)

    Mohammad Aminul Islam

    Full Text Available ABSTRACT VC (20%, TC (20% and N:P:K fertilizer (farmer's practice were used to determine the growth and yield attributes of bush bean (Phaseolus vulgaris, winged bean (Psophocarpus tetragonolobus and yard long bean (Vigna unguiculata. Plants grown with VC (20% produced the highest fresh biomass for bush bean (527.55 g m-2, winged bean (1168.61 g m-2 and yard long bean (409.84 g m-2. In all the tested legumes the highest pod weight, pod number, pod dry weight and pod length were found in the VC (20% treatment. Photosynthetic rates in the three legumes peaked at pod formation stage in all treatments, with the highest photosynthetic rate observed in winged bean (56.17 µmol m-2s-1 grown with VC (20%. The highest yield for bush bean (2.98 ton ha-1, winged bean (7.28 ton ha-1 and yard long bean (2.22 ton ha-1 were also found in VC (20% treatment. Furthermore, protein content was highest in bush bean (26.50 g/100g, followed by yard long bean (24.74 g/100g and winged bean (22.04 g/100g, under VC (20% treatment. It can be concluded that legumes grown with VC (20% produced the highest yield and yield attributes.

  9. Serious envenomation after a snakebite by a Western bush viper (Atheris chlorechis) in the Netherlands : a case report

    NARCIS (Netherlands)

    Top, LJ; Tulleken, JE; Ligtenberg, JJM; van der Werf, TS; Zijlstra, JG; Meertens, John H. J. M.

    2006-01-01

    Venomous snakebites are a rarity in the Netherlands. In this report we describe the case of a 26-year-old male amateur snakekeeper who was bitten in his left index finger by a Western bush viper (Atheris chlorechis). His clinical condition deteriorated rapidly with acute renal failure and considerab

  10. The economics of landscape restoration: Benefits of controlling bush encroachment and invasive plant species in South Africa and Namibia

    CSIR Research Space (South Africa)

    Stafford, William

    2017-01-01

    Full Text Available number of ecosystem services from landscape restoration in South Africa and Namibia. In Namibia, the estimated value of ecosystem services from the restoration of bush encroachment was US$5.8 billion. In South Africa, the estimated value of ecosystem...

  11. The bush-cricket Isophya kraussii (Orthoptera: Phaneropteridae): bioacoustics, distribution and description of a new subspecies from Romania.

    Science.gov (United States)

    Iorgu, Ionuţ Ştefan; Heller, Klaus-Gerhard

    2013-01-01

    Isophya kraussii Brunner von Wattenwyl, 1878, one of the widest spread bush-crickets within this genus, is confirmed to be present east of the Carpathian Mountains. Based on acoustic analysis and morphological characters, the populations from NE Romania are considered to belong to a different subspecies, I. kraussii moldavica ssp. n. A map with distribution of both subspecies is presented.

  12. Automatic classification of Google Earth images for a larger scale monitoring of bush encroachment in South Africa

    Science.gov (United States)

    Ludwig, Annika; Meyer, Hanna; Nauss, Thomas

    2016-08-01

    Bush encroachment of savannas and grasslands is a common form of land degradation in the rangelands of South Africa. To assess the carrying capacity of the land and to understand underlaying processes of bush encroachment, continuous monitoring of this phenomenon is needed. The aim of this study is to provide training sites for satellite-based monitoring of bush encroachment in South Africa on a medium spatial resolution satellite sensor (e.g. MODIS or Landsat) scale. Since field surveys are time consuming and of limited spatial extent, the satellite based creation of training sites using Google Earth images is intended. Training pixels for woody vegetation and non-woody land cover were manually digitized from 50 sample Google Earth images. A Random Forests model was trained to delineate woody from non-woody pixels. The results indicate a high performance of the model (AUC = 0.97). The model was applied to a further 500 Google Earth images with a spatial extent of 250 m × 250 m. The classified images form the database of training sites which can be used for larger scale monitoring of bush encroachment in South Africa.

  13. Odorants of the Flowers of Butterfly Bush, Buddleia davidii as Possible Attractants of Pest Species of Moths

    Science.gov (United States)

    Flowers of the butterfly bush, Buddleia davidii Franch., are visited by butterflies and moths, as well as other insects. Moths captured in traps over flowers were 21 species of Geometridae, Noctuidae, Pyralidae, and Tortricidae. The most abundant moths trapped at these flowers were the cabbage loop...

  14. President Bush : langenud nõuavad, et me jätkame võitlust! / Tõnis Erilaid

    Index Scriptorium Estoniae

    Erilaid, Tõnis, 1943-

    2005-01-01

    Salt Lake Citys USA sõjaveteranidele peetud kõnes ütles USA president George W. Bush, et tuleb jõuda eesmärgile, mille eest USA sõdurid oma elu andsid. Samas toimus sõjavastaste demonstratsioon

  15. Cavitation as a Precursor to Breakdown of Mass-Impregnated HVDC Cables

    Energy Technology Data Exchange (ETDEWEB)

    Evenset, Gunnar

    1999-09-01

    Thermal cycling has proven to be a critical test for mass-impregnated HVDC cables. The dielectric strength of the insulation is significantly reduced during the first part of the cooling. This decrease of the dielectric strength limits the development of mass-impregnated cables for higher operating voltages and higher power transfer capacities. The decrease of the dielectric strength during cooling has been assumed to be caused by formation of cavities in the mass because the thermal contraction of the mass is larger than that of the paper. Cavities have previously been observed in thermally cycled cables, but their actual formation and growth have not been studied. The fact that breakdown usually occurs a few hours into the cooling period indicates that the dynamics of the growth is important. This work studies the dynamic phenomena occurring in mass-impregnated cables during thermal cycling. In experiments on a system of mass and insulating paper, cavities were observed near the paper surface, probably caused by heterogeneous nucleation. Knowing the tensile stress at cavity formation is important because it controls the size of the cavities and the distance between independently formed cavities in a cable insulation. A test cell was designed to investigate cavitation in models of lapped insulation. The formation, growth and collapse of the cavities could be visually observed while the insulation was electrically stressed and partial discharges were measured. The first cavity generally formed in one of the butt gaps and grew both along the butt gap and into the mass layers between the papers towards adjacent butt gaps. When the cavity between the papers grew into an adjacent butt gap, the gas/vapour filled channel connecting the butt gaps was closed. In this way, one cavity grew into several butt gaps. The extent of cavities between the papers was observed to depend on the interfacial pressure. Considerable less tension is required to suck the menisci of a cavity

  16. Crimes et châtiments dans le monde de la finance pendant les années Bush Crime and Punishment in the World of Finance during the Bush Administration

    Directory of Open Access Journals (Sweden)

    Régine Hollander

    2010-03-01

    Full Text Available Le premier mandat de George W. Bush est ébranlé par une série de scandales dans le monde de l’entreprise et de la finance qui provoque une vague de réformes au sein du Congrès et des autorités de réglementation. La loi Sarbanes-Oxley, votée en 2002, a pour but d’accroître les contrôles financiers et de prévenir la fraude. Simultanément un dispositif répressif, destiné à prouver que le crime ne paie pas et à redonner confiance aux petits investisseurs, est mis en place. Les entreprises paient de lourdes amendes, mais les individus sont aussi mis au banc des accusés. Armé du Martin Act qui lui donne de larges pouvoirs, le Procureur Général de l’État de New York, Eliot Spitzer, poursuit sans relâche les coupables. On fait appel au sens moral de chacun et encourage la dénonciation. Cependant Sarbanes-Oxley a des effets pervers sur l’activité des marchés financiers. Elle décourage les introductions en bourse sur la place de New York et incite les entreprises à sortir de la cote. Des voix s’élèvent pour réclamer une déréglementation qui rendrait la place de New York plus attractive pour les entreprises. Mais voilà qu’en septembre 2008, la tourmente née de la titrisation des crédits à risque déclenche un maelström qui engouffre les institutions les plus prestigieuses de Wall Street. Les régulateurs reprennent l’avant de la scène et le risque est nationalisé, punissant les contribuables d’un crime dont ils ne se sentent pas responsables. L’effet de la crise financière sur l’économie réelle impose un changement de paradigme. Il ne s’agit plus de châtier, mais de sauver un secteur bancaire en désarroi pour préserver le mode de vie des Américains.George W. Bush’s first presidential term was shaken by a series of scandals in the corporate and financial world. Congress and regulatory authorities responded by enacting a wave of reforms. The Sarbanes-Oxley Act, passed in 2002, aimed at

  17. Quality Control of Extruded HVDC Cables: Detection of Critical Flaws Using Low Frequency Voltage Endurance Testing%Quality Control of Extruded HVDC Cables: Detection of Critical Flaws Using Low Frequency Voltage Endurance Testing

    Institute of Scientific and Technical Information of China (English)

    Erling Ildstad; Frank Mauseth; Mildrid Selsjord; Roll Hegerberg

    2011-01-01

    The main purpose of the work presented here is to evaluate different methods for quality control of polymer- ic insulated HVDC cables. The insight gained can be used to evaluate proposed test methods for quality assurance of long lengths of polymer insulated power cables. Laboratory experiments were performed using both Rogowski shaped test objects and model cables, insulated with XLPE containing imbedded spherically shaped particles. Tests were per- formed by stressing the test object with AC (50 Hz), VLF (0.1 Hz) and DC voltages and measuring time to break- down at the different voltages. The slope of the voltage-time curve for 0. land 50 Hz were found to be parallel show- ing higher breakdown strength for 0.1 Hz than 50 Hz. The number of periods to breakdown is somewhat higher for 0.1 Hz than for 50 Hz. The breakdown strength for DC was~ much higher than for both AC 50 Hz and 0.1 Hz. The results indicate that the VLF test voltage needs to be 2 to 3 times higher than at 50 Hz power frequency in order to eliminate the same defects within a comparable time.

  18. Fruit quality parameters of some southern high bush blueberries (Vaccinium xcorymbosum L.) grown in Andalusia (Spain)

    Energy Technology Data Exchange (ETDEWEB)

    Molina, J. M.; Calvo, D.; Medina, J. J.; Barrau, C.; Romero, E.

    2008-07-01

    Physical and chemical parameters of fresh berries from three southern high bush (ONeal, Sharp blue and Misty) blueberry cultivars grown in Huelva (Southwestern Spain) under two production systems were measured and evaluated. ANOVA applied to data yielded significant differences between production systems for mean fruit size and mean fruit fresh weight (P<0.05), although main effects on physical and chemical characteristics of fruit were due to cultivar. All three cultivars showed significantly different means (P<0.05) for fruit fresh weight, and all chemical characteristics. Stepwise discriminant analysis (SDA) for classification and identification of the cultivars based on physico-chemical properties of samples of fruits was performed. The model obtained gave high percentages of correct classification and prediction (81.1% and 78.4%, respectively). The variables with higher discriminating power were fruit titratable acidity, fruit size and fruit sugar content. (Author)

  19. Fiddler on the tree--a bush-cricket species with unusual stridulatory organs and song.

    Directory of Open Access Journals (Sweden)

    Klaus-Gerhard Heller

    Full Text Available Insects of the order Orthoptera are well-known for their acoustic communication. The structures used for this purpose show a high diversity which obviously relates to differences in song parameters and to the physics of sound production. Here we describe song and morphology of the sound producing organs of a tropical bush-cricket, Ectomoptera nepicauda, from East Africa. It has a very unusual calling song consisting of frequency-modulated, pure-tone sounds in the high ultrasonic range of 80 to 120 kHz and produced by extremely fast wing movements. Concerning morphology, it represents the most extreme state in the degree of left-right fore-wing differentiation found among Orthoptera: the acoustic parts of the left fore-wing consist exclusively of the stridulatory file, comparable in function to the bow of a violin, while the right wing carries only the plectrum ( =  string and mirror ( =  soundbox.

  20. Wolves at the Door: Musical persuasion in a 2004 Bush-Cheney advertisement

    Directory of Open Access Journals (Sweden)

    Matthew A. Killmeier

    2010-10-01

    Full Text Available Many journalists and scholars overlook the discursive role of music in TV political advertisements. But we argue that music is a potent means of political persuasion. Music in advertisements is determinative; all other elements—images, voiceovers, sound effects, written text, and so on—are circumscribed by the music and interpreted in relation to it. Music determines an advertisement’s character through framing and underscoring; musical frames establish interpretative categories and generate expectations, while underscoring comprises music that closely coordinates with images and voiceovers to form a persuasive aesthetic and rhetorical unity. A close reading of a 2004 Bush-Cheney advertisement applies this theory of frames and underscoring to explain the advertisement’s effectiveness. Without music, the advertisement would not only fail to persuade, it would also make no sense.

  1. Eland browsing of Grewia occidentalis in semi-arid shrubland: the influence of bush clumps

    Directory of Open Access Journals (Sweden)

    L.H. Watson

    1999-01-01

    Full Text Available Grewia occidentalis plants in the study area generally occurred in bush clumps with other shrub species. Grewia occidentalis commonly occurred with Diospyros austro-africana, Rhus longispina and Rhus pollens (nurse shrubs, but seldom with Acacia kar-roo and Lycium cinereum (non-nurse shrubs. Eland browsed G. occidentalis plants at higher levels than other shrub species, but browsing was not evenly spread across all plants. Grewia occidentalis plants associated with nurse shrubs had lower levels of browsing than those growing alone and those growing with non-nurse shrubs, while G. occidentalis plants in the centre of nurse shrubs experienced the lowest levels of browsing. The latter group of plants also produced the most fruit. Eland browsing is consid-ered an important factor determining the distribution of G. occidentalis plants in the study area, while the presence of nurse shrubs is considered essential for the establishment and maintenance of the G. occidentalis population in the study area.

  2. Masoprocol (nordihydroguaiaretic acid): a new antihyperglycemic agent isolated from the creosote bush (Larrea tridentata).

    Science.gov (United States)

    Luo, J; Chuang, T; Cheung, J; Quan, J; Tsai, J; Sullivan, C; Hector, R F; Reed, M J; Meszaros, K; King, S R; Carlson, T J; Reaven, G M

    1998-04-03

    An ethnomedically-driven approach was used to evaluate the ability of a pure compound isolated from the creosote bush (Larrea tridentata) to lower plasma glucose concentration in two mouse models of type 2 diabetes. The results indicated that plasma glucose concentration fell approximately 8 mmol/l in male C57BL/ks-db/db or C57BL/6J-ob/ob mice following the oral administration of masoprocol (nordihydroguaiaretic acid), a well known lipoxygenase inhibitor. The decline in plasma glucose concentration following masoprocol treatment in the mice was achieved without any change in plasma insulin concentration. In addition, oral glucose tolerance improved and the ability of insulin to lower plasma glucose concentrations was accentuated in masoprocol-treated db/db mice. These data raise the possibility that masoprocol, or other lipoxygenase inhibitors, represents a new approach to the pharmacological treatment of Type 2 diabetes.

  3. Wall to Wall Optimal Transport

    CERN Document Server

    Hassanzadeh, Pedram; Doering, Charles R

    2013-01-01

    The calculus of variations is employed to find steady divergence-free velocity fields that maximize transport of a tracer between two parallel walls held at fixed concentration for one of two constraints on flow strength: a fixed value of the kinetic energy or a fixed value of the enstrophy. The optimizing flows consist of an array of (convection) cells of a particular aspect ratio Gamma. We solve the nonlinear Euler-Lagrange equations analytically for weak flows and numerically (and via matched asymptotic analysis in the fixed energy case) for strong flows. We report the results in terms of the Nusselt number Nu, a dimensionless measure of the tracer transport, as a function of the Peclet number Pe, a dimensionless measure of the energy or enstrophy of the flow. For both constraints the maximum transport Nu_{MAX}(Pe) is realized in cells of decreasing aspect ratio Gamma_{opt}(Pe) as Pe increases. For the fixed energy problem, Nu_{MAX} \\sim Pe and Gamma_{opt} \\sim Pe^{-1/2}, while for the fixed enstrophy scen...

  4. LA IDEOLOGÍA NEOCONSERVADORA Y EL GOBIERNO DE GEORGE W. BUSH

    Directory of Open Access Journals (Sweden)

    John Saxe Fernández

    2004-07-01

    Full Text Available El 15 de Septiembre de 2002, casi al año de los ataques contra las Torres Gemelas y el Pentágono,el Sunday Herald informó sobre la existencia de un plan elaborado por un instituto “neo-conservador”,ese es el término usado en la nota periodística,identificado como el “Proyecto para un Nuevo Siglo Estadounidense”, que empezó a funcionar en1997.Este instituto se orientó al impulso de lo que su documento fundacional califica como “una política reaganiana de fortaleza militar y de claridad moral”, considerada como algo “necesario para que EUA, basado en los éxitos del siglo pasado, consolide nuestra seguridad y nuestra grandeza en el próximo siglo”. El documento, de línea ultranacionalista, plantea la “creación de una Pax Americana Global”, y fue endosado por DickCheney, Donald Rumsfeld, Paul Wolfowitz, JeffBush y Lewis Lobby, jefe del personal de Cheney, con la participación de operadores políticos eideólogos como Elliott Abrams y Francis Fukuyama. El Sunday Herald enfatizó que, según el documento, “antes de que asumiera la presidencia en Enero de 2000, Bush y su gabineteya estaban contemplando y planeando un “cambio de régimen” en Irak por medio de un ataque premeditado contra ese país.

  5. Frequency processing at consecutive levels in the auditory system of bush crickets (tettigoniidae).

    Science.gov (United States)

    Ostrowski, Tim Daniel; Stumpner, Andreas

    2010-08-01

    We asked how processing of male signals in the auditory pathway of the bush cricket Ancistrura nigrovittata (Phaneropterinae, Tettigoniidae) changes from the ear to the brain. From 37 sensory neurons in the crista acustica single elements (cells 8 or 9) have frequency tuning corresponding closely to the behavioral tuning of the females. Nevertheless, one-quarter of sensory neurons (approximately cells 9 to 18) excite the ascending neuron 1 (AN1), which is best tuned to the male's song carrier frequency. AN1 receives frequency-dependent inhibition, reducing sensitivity especially in the ultrasound. When recorded in the brain, AN1 shows slightly lower overall activity than when recorded in the prothoracic ganglion close to the spike-generating zone. This difference is significant in the ultrasonic range. The first identified local brain neuron in a bush cricket (LBN1) is described. Its dendrites overlap with some of AN1-terminations in the brain. Its frequency tuning and intensity dependence strongly suggest a direct postsynaptic connection to AN1. Spiking in LBN1 is only elicited after summation of excitatory postsynaptic potentials evoked by individual AN1-action potentials. This serves a filtering mechanism that reduces the sensitivity of LBN1 and also its responsiveness to ultrasound as compared to AN1. Consequently, spike latencies of LBN1 are long (>30 ms) despite its being a second-order interneuron. Additionally, LBN1 receives frequency-specific inhibition, most likely further reducing its responses to ultrasound. This demonstrates that frequency-specific inhibition is redundant in two directly connected interneurons on subsequent levels in the auditory system.

  6. Buffalo, bush meat, and the zoonotic threat of brucellosis in Botswana.

    Directory of Open Access Journals (Sweden)

    Kathleen Anne Alexander

    Full Text Available BACKGROUND: Brucellosis is a zoonotic disease of global importance infecting humans, domestic animals, and wildlife. Little is known about the epidemiology and persistence of brucellosis in wildlife in Southern Africa, particularly in Botswana. METHODS: Archived wildlife samples from Botswana (1995-2000 were screened with the Rose Bengal Test (RBT and fluorescence polarization assay (FPA and included the African buffalo (247, bushbuck (1, eland (5, elephant (25, gemsbok (1, giraffe (9, hartebeest (12, impala (171, kudu (27, red lechwe (10, reedbuck (1, rhino (2, springbok (5, steenbok (2, warthog (24, waterbuck (1, wildebeest (33, honey badger (1, lion (43, and zebra (21. Human case data were extracted from government annual health reports (1974-2006. FINDINGS: Only buffalo (6%, 95% CI 3.04%-8.96% and giraffe (11%, 95% CI 0-38.43% were confirmed seropositive on both tests. Seropositive buffalo were widely distributed across the buffalo range where cattle density was low. Human infections were reported in low numbers with most infections (46% occurring in children (<14 years old and no cases were reported among people working in the agricultural sector. CONCLUSIONS: Low seroprevalence of brucellosis in Botswana buffalo in a previous study in 1974 and again in this survey suggests an endemic status of the disease in this species. Buffalo, a preferred source of bush meat, is utilized both legally and illegally in Botswana. Household meat processing practices can provide widespread pathogen exposure risk to family members and the community, identifying an important source of zoonotic pathogen transmission potential. Although brucellosis may be controlled in livestock populations, public health officials need to be alert to the possibility of human infections arising from the use of bush meat. This study illustrates the need for a unified approach in infectious disease research that includes consideration of both domestic and wildlife sources of

  7. 直流输电系统强迫停运探讨%Discussion on forced outages of HVDC transmission system

    Institute of Scientific and Technical Information of China (English)

    朱韬析; 李娟; 王超; 陈为化

    2009-01-01

    There are many protection and monitoring functions in HVDC transmission system. Although the equipments are completely protected, the mal-operation is very difficult to be avoided. In this paper, based on the experiences of Tian-Guang HVDC transmission system, the forced outage and the protection and monitoring which would cause forced outage are introduced first, then the reason caused forced outages in operation in those years and its effect are analyzed. At last, combined with the safety of equipments and the reliability of power system, the improving suggestion to the protection and monitoring function in HVDC transmission system is discussed.%直流输电系统中设置了大量的保护、监视功能,但在确保设备安全的同时,也带来了容易误动的隐患.以天广直流输电系统为例,首先介绍了直流输电系统的强迫停运及可能引起强迫停运的保护监视功能,接着讨论了多年来运行中发生的强迫停运故障原因及故障时对设备的影响,最后综合考虑设备的安全和电网的稳定,对直流输电系统的保护、监视功能提出了改进建议.

  8. 低电平MMC-HVDC样机滤波装置设计%Design of Filtering Device for Low Level Prototype of MMC-HVDC

    Institute of Scientific and Technical Information of China (English)

    王卫安; 桂卫华

    2011-01-01

    为了确保低电平模块化多电平换流器直流输电(MMC-HVDC)样机注入公共电网的谐波含量符合现有的电能质量标准条例,对其进行配套的滤波装置设计是必要的.文章根据MMC拓扑结构特点,推导出了MMC的等值电路,并将MMC看成一个有多种谐波的谐波电压源,从而设计了MMC交流侧谐波的等效电路.在此基础上,结合MMC-HVDC的调制策略,设计出了与样机配套的滤波装置,仿真结果表明了其滤波装置设计方法的正确性.%In order to ensure the harmonic of common electric network injected by low level prototype of modular multilevel converter high voltage direct current (MMC-HVDC) could accord with existing electric power quality standard regulations, it is necessary to design filtering devices for the prototype. According to the topology structure of MMC, an equivalent circuit was deduced, and regarding MMC as one harmonic source con-tairfing multiform harmonics, the equivalent circuit which could calculate the harmonic at AC side of MMC was obtained. Based on above, and combined with modulation strategy of MMC-HVDC, the filters for the prototype were designed. Simulation results show the method to design the filtering devices is correct.

  9. Control and operation of wind turbine converters during faults in an offshore wind power plant grid with VSC-HVDC connection

    DEFF Research Database (Denmark)

    Chaudhary, Sanjay; Teodorescu, Remus; Rodriguez, Pedro

    2011-01-01

    ). Current limit control enables the GSC to sustain the fault currents during short circuits in the offshore wind collector system grid. However, power transmission is affected, and the fault has to be isolated. It can be resynchronized after the fault has been cleared and the breaker reclosed. Healthy WTG......Voltage source converter (VSC) based high voltage dc (HVDC) transmission is an attractive technique for large offshore wind power plants, especially when long cable transmission is required for connection to the onshore grid. New multi-MW wind turbines are likely to be equipped with full scale...

  10. U.S. Embargo Walls Us In

    Science.gov (United States)

    Durand, Cliff; McGuire, Mike

    2004-01-01

    On June 30, the Bush administration imposed new regulations sharply curtailing already-limited travel to Cuba. A New York Times article published on June 24 characterized the regulations as "part of a broader plan that President Bush announced last month to be tougher on President Fidel Castro and speed a transition to democracy in Cuba.…

  11. Integrative taxonomy of the Russet Bush Warbler Locustella mandelli complex reveals a new species from central China

    Institute of Scientific and Technical Information of China (English)

    Per; Alstr?m; Canwei; Xia; Pamela; C; Rasmussen; Urban; Olsson; Bo; Dai; Jian; Zhao; Paul; J; Leader; Geoff; J; Carey; Lu; Dong; Tianlong; Cai; Paul; I; Holt; Hung; Le; Manh; Gang; Song; Yang; Liu; Yanyun; Zhang; Fumin; Lei

    2015-01-01

    Background: The Russet Bush Warbler Locustella(previously Bradypterus) mandelli complex occurs in mountains in the eastern Himalayas, southern China, Vietnam, the Philippines, and Indonesia. The taxonomy has been debated,with one(L. seebohmi) to four(L. seebohmi, L. mandelli, L. montis and L. timorensis) species having been recognised.Methods: We used an integrative approach, incorporating analyses of morphology, vocalizations and a molecular marker, to re-evaluate species limits in the L. mandelli complex.Results: We found that central Chinese L. mandelli differed from those from India through northern Southeast Asia to southeast China in plumage, morphometrics and song. All were easily classified by song, and(wing + culmen)/tail ratio overlapped only marginally. Both groups were reciprocally monophyletic in a mitochondrial cytochrome b(cytb) gene tree, with a mean divergence of 1.0 ± 0.2%. They were sympatric and mostly altitudinally segregated in the breeding season in southern Sichuan province. We found that the Mt Victoria(western Myanmar) population differed vocally from other L. mandelli, but no specimens are available. Taiwan Bush Warbler L. alishanensis was sister to the L. mandelli complex, with the most divergent song. Plumage, vocal and cytb evidence supported the distinctness of the south Vietnamese L. mandelli idonea. The Timor Bush Warbler L. timorensis, Javan Bush Warbler L.montis and Benguet Bush Warbler L. seebohmi differed distinctly in plumage, but among-population song variation in L. montis exceeded the differences between some populations of these taxa, and mean pairwise cytb divergences were only 0.5–0.9%. We also found that some L. montis populations differed morphologically.Conclusions: We conclude that the central Chinese population of Russet Bush Warbler represents a new species,which we describe herein, breeding at mid elevations in Sichuan, Shaanxi, Hubei, Hunan and Guizhou provinces.The taxonomic status of the other allopatric

  12. Integrative taxonomy of the Russet Bush Warbler Locustella mandelli complex reveals a new species from central China

    Institute of Scientific and Technical Information of China (English)

    Per Alström; Tianlong Cai1; Paul I Holt; Hung Le Manh; Gang Song; Yang Liu; Yanyun Zhang; Fumin Lei; Canwei Xia; Pamela C Rasmussen; Urban Olsson; Bo Dai; Jian Zhao; Paul J Leader; Geoff J Carey; Lu Dong

    2015-01-01

    Background:The Russet Bush Warbler Locustel a (previously Bradypterus) mandel i complex occurs in mountains in the eastern Himalayas, southern China, Vietnam, the Philippines, and Indonesia. The taxonomy has been debated, with one (L. seebohmi) to four (L. seebohmi, L. mandel i, L. montis and L. timorensis) species having been recognised. Methods:We used an integrative approach, incorporating analyses of morphology, vocalizations and a molecular marker, to re-evaluate species limits in the L. mandel i complex. Results:We found that central Chinese L. mandel i differed from those from India through northern Southeast Asia to southeast China in plumage, morphometrics and song. All were easily classified by song, and (wing+culmen)/tail ratio overlapped only marginally. Both groups were reciprocally monophyletic in a mitochondrial cytochrome b (cytb) gene tree, with a mean divergence of 1.0 ± 0.2%. They were sympatric and mostly altitudinally segregated in the breeding season in southern Sichuan province. We found that the Mt Victoria (western Myanmar) population differed vocally from other L. mandel i, but no specimens are available. Taiwan Bush Warbler L. alishanensis was sister to the L. mandel i complex, with the most divergent song. Plumage, vocal and cytb evidence supported the distinctness of the south Vietnamese L. mandel i idonea. The Timor Bush Warbler L. timorensis, Javan Bush Warbler L. montis and Benguet Bush Warbler L. seebohmi differed distinctly in plumage, but among-population song variation in L. montis exceeded the differences between some populations of these taxa, and mean pairwise cytb divergences were only 0.5–0.9%. We also found that some L. montis populations differed morphologically. Conclusions:We conclude that the central Chinese population of Russet Bush Warbler represents a new species, which we describe herein, breeding at mid elevations in Sichuan, Shaanxi, Hubei, Hunan and Guizhou provinces. The taxonomic status of the other

  13. Auxiliary Equipment Based Processing Strategy for MMC-HVDC DC Faults%基于辅助电路的 MMC-HVDC 直流故障处理策略

    Institute of Scientific and Technical Information of China (English)

    郭敬梅; 曾德辉; 王钢; 李海锋

    2016-01-01

    直流线路故障是基于模块化多电平换流器的高压直流输电(MMC‐HVDC)系统必须解决的关键问题。文中提出一种基于辅助电路的直流故障处理策略,即双向晶闸管与开关型零损耗限流装置相配合的保护方案。首先分析了直流故障电流自然衰减的直流保护原理及现有方案的缺陷,进而提出采用双向晶闸管代替背靠背晶闸管集中配置在交流侧的方法来简化其控制回路;通过与开关型零损耗限流装置相配合,并对限流电抗器进行合理设计,能够使保护在不增加运行损耗的同时具有快速抑制短路电流的能力,降低清除直流故障时对交流系统长时间的冲击。此外,进一步提出相应的故障检测及恢复策略。最后,基于 PSCAD 仿真平台验证了所述保护方案的有效性。%The DC‐link fault is a key issue for the flexible high‐voltage direct current system using modular multilevel converter ( MMC‐HVDC) . An auxiliary equipment based processing strategy for MMC‐HVDC DC faults is proposed , namely , a novel scheme by bidirectional thyristors in collaboration with a breaker‐type zero‐loss fault current limiter . The DC‐protections based on natural decay of the fault DC current and their shortcomings are analyzed first . It is then proposed that the bidirectional thyristors rather than back‐to‐back ones are configured and controlled on the AC‐side to simplify the control loop . The bidirectional thyristors are controlled to cooperate with the appropriately designed breaker‐type zero‐loss fault current limiter , which can possess fast current limiting ability while reducing the long short‐circuit current rush to AC system during the clearance of the DC‐link fault . And the corresponding DC‐fault detection and recovery strategy is presented . PSCAD based simulation results finally verify the validity of the proposed protection scheme .

  14. Production of Antioxidant Nutraceuticals by Solid-State Cultures of Pomegranate (Punica granatum Peel and Creosote Bush (Larrea tridentata Leaves

    Directory of Open Access Journals (Sweden)

    Cristóbal Noé Aguilar

    2008-01-01

    Full Text Available In this work, creosote bush (Larrea tridentata leaves and pomegranate (Punica granatum peels were characterized for their use as a source of antioxidants and a support in solid-state fermentation. This work focuses on the kinetic evaluation of physicochemical changes during the fungal fermentation of two tannin-rich plant materials, mainly on the polyphenolic content. Aspergillus niger GH1 was used in the fermentation processes, the cultures were monitored for 96 h. The content of proteins, crude fibres, lipids, reducing and total sugars was evaluated following the AOAC methods. Tannins were analyzed using a spectrophometric method. Biodegradation of ellagitannins was monitored kinetically and the accumulation of gallic and ellagic acids was determined by HPLC. Results demonstrated that pomegranate peel and creosote bush leaves are excellent supports for solid-state fermentation and sources of antioxidants.

  15. Larrea tridentata (Creosote bush), an abundant plant of Mexican and US-American deserts and its metabolite nordihydroguaiaretic acid.

    Science.gov (United States)

    Arteaga, Silvia; Andrade-Cetto, Adolfo; Cárdenas, René

    2005-04-26

    Although controversial, Creosote bush, Larrea tridentata (Sesse and Moc. ex DC) Coville, is used to treat a variety of illnesses including infertility, rheumatism, arthritis, diabetes, gallbladder and kidney stones, pain and inflammation. Recently, it has been used as a nutritional supplement. The primary product extracted from this common plant of the arid regions of northern Mexico and Southwestern United States is the potent antioxidant nordihydroguaiaretic acid (NDGA). It was widely used during the 1950s as a food preservative and to preserve naturals fibers. Later it was banned after reports of toxicity during the early 1960s. Renal and hepatotoxicity are also reported for chronic use of creosote bush and NDGA. This article reviews traditional and contemporary uses and pharmacology, including toxicology of this plant widely used in Mexican traditional medicine.

  16. The Bush/Cheney Energy Strategy: Implications for U.S. Foreign and Military Policy

    Energy Technology Data Exchange (ETDEWEB)

    Klare, Michael T. [Hampshire College, Amherst, MA (United States). Peace and World Security Studies

    2003-07-01

    The 'National Energy Policy' (NEP) released by the Bush Administration on May 17, 2001 was supposedly intended to meet growing U.S. energy requirements in the first two decades of the 21st Century while also diminishing U.S. dependence on imported oil. This was to be accomplished, the White House suggested, by increasing production at existing oil fields in the United States and by commencing drilling on the Artic National Wildlife Refuge (ANWR) in Alaska. So great was the furor over drilling on ANWR that most people never bothered to examine the NEP closely. This is unfortunate, as a close reading of the NEP report reveals a very different picture than that suggested by White House pronouncements: far from promoting energy 'independence', the NEP assumes that the United States will become MORE, not less dependent on imported petroleum in the years ahead and therefore calls on the Federal Government to take whatever steps are necessary to promote enhanced U.S. access to foreign oil. In particular, the NEP calls on the U.S. Government to seek additional petroleum from the Persian Gulf area, Russia, the Caspian Sea basin, Mexico, Venezuela, Angola, and Nigeria. As is implied by the report, the United States must acquire more oil from these countries in order to permit increased oil consumption in the United States at a time of declining domestic production. Even leaving aside the question of whether these countries will be able to boost their production sufficiently to satisfy steadily rising demand in the United States, this strategy poses enormous challenges for the United States because most of these areas are highly unstable and house anti-American governments and forces. It is likely, then, that U.S. efforts to acquire more oil from these countries will entail the increased presence of U.S. military forces in the area and periodic U.S. military intervention. Indeed, the requirement for increased military action in support of U.S. foreign

  17. New imperialism and beyond: why the new imperialism will fail and unseat the Bush Administration?

    Directory of Open Access Journals (Sweden)

    Petri Minkkinen

    2008-12-01

    Full Text Available Tras los atentados terroristas del 11S de 2001, los Estados Unidos implantaron una política de nuevo imperialismo y de construcción de un nuevo tipo de imperio mundial. Las políticas globales norteamericanas pueden dividirse en economista, cooperativista y reglada por el idealismo Wilsoneano, y el imperialismo Rooseveltiano, basado en un nacionalismo agresivo, militarismo, unilateralismo y governanza global  basada en reglas directas, presencia física y coerción. Las políticas de la administraciones Bush representan esta última vertiente y la Guerra contra el Terror puede ser interpretada como una Primera Guerra Mundial y una guerra civil en los Estados Unidos. Se proclama que un nuevo imperialismo fracasará debido a diversas razones de tipo económica, política, étnica e histórica, y que esta política está debilitando la posición global de Estados Unidos. Al final, se explica cómo en el contexto de una Nueva Contención Pacífica, los ciudadanos norteamericanos y los ciudadanos del resto del mundo pueden utilizar la democracia en contra del nuevo imperialismo y apoyar un cambio de régimen democrático en Estados Unidos, procediendo a la construcción conjunta de un  mundo democrático y justo.________________ABSTRACT:After the terrorist attacks of S-11-2001 the US engaged in the policies of new imperialism and in the construction of a new kind of world-empire. US global policies can be divided in detached, economist, cooperative, rule-based Wilsonian Idealism and Theodore Rooseveltian Imperialism, based on aggressive nationalism, militarism, unilateralism and global governance based on direct rule, physical presence and coercion. The Bush administrations policies represent the latter and the War on Terror and Non-White Others can be seen as a First World War and an Internal Civil War in the US. It is claimed that the new imperialism will fail due to various economic, political, ethical and historical reasons and that this

  18. An adaptive neuro fuzzy inference system controlled space cector pulse width modulation based HVDC light transmission system under AC fault conditions

    Science.gov (United States)

    Ajay Kumar, M.; Srikanth, N.

    2014-03-01

    In HVDC Light transmission systems, converter control is one of the major fields of present day research works. In this paper, fuzzy logic controller is utilized for controlling both the converters of the space vector pulse width modulation (SVPWM) based HVDC Light transmission systems. Due to its complexity in the rule base formation, an intelligent controller known as adaptive neuro fuzzy inference system (ANFIS) controller is also introduced in this paper. The proposed ANFIS controller changes the PI gains automatically for different operating conditions. A hybrid learning method which combines and exploits the best features of both the back propagation algorithm and least square estimation method is used to train the 5-layer ANFIS controller. The performance of the proposed ANFIS controller is compared and validated with the fuzzy logic controller and also with the fixed gain conventional PI controller. The simulations are carried out in the MATLAB/SIMULINK environment. The results reveal that the proposed ANFIS controller is reducing power fluctuations at both the converters. It also improves the dynamic performance of the test power system effectively when tested for various ac fault conditions.

  19. 高压直流输电用无源型直流转换开关电弧电流特性研究%Arc Current Characteristic of DC Circuit Breaker in HVDC Transmission and Distribution System

    Institute of Scientific and Technical Information of China (English)

    那虎; 丁正平; 孙晋峰; 杨俊清; 刘龙开; 袁芳; 洪深

    2012-01-01

    直流输变电系统用无源型高压直流转换开关是直流系统中的重要运行设备,其运行工况及工作特性极其特殊.笔者通过对高压直流转换开关工作原理及工况进行研究,并依据试验测得的断口电弧电流曲线的特征,对高压直流转换开关开断转换电流的电弧电流特性进行理论研究及分析,给出了电弧电流特性函数,指出高压直流转换开关开断的关键点是断口的弧阻小,变化率大,L1C1辅助支路频率高,才能开断较大的直流电流.%The passive high-voltage direct current (HVDC)circuit breaker is important for ensuring reliability of HVDC distribution system, and its working condition and characteristic are particular. In this paper, the working condition and characteristic of HVDC circuit breaker in HVDC transmission and distribution system are analyzed, the arc current characteristic of the breaker is investigated according to test data, and a function for describing arc current characteristic of the breaker is achieved. Conclusion is drawn that small arcing resistance, high varying rate, and high frequency of L1C1 circuit can facilitate breaking larger direct current by HVDC circuit breaker.

  20. Vannevar Bush 2: Science for the 21st Century. Why Should Federal Dollars be Spent to Support Scientific Research?

    Science.gov (United States)

    Miller, Kate (Editor)

    1995-01-01

    On July 5, 1945, Dr. Vannevar Bush delivered a report to President Truman known as 'Science: The Endless Frontier'. In the report, Dr. Bush stated that 'scientific progress is one essential key to our security as a nation, to our better health, to more jobs, to a higher standard of living, and to our cultural progress'. Bush addressed job creation, the independence of basic research, the ties between research and application, and the nations's need for new talent. In 1995, there are strong similarities between the issues addressed in the Congress, Administration, and the public and those following World War 2. Federal funds and research funding are under severe pressure, including that from fiscal constraints in the federal budget due to the large and growing deficit and the escalating cost of health care. Defense conversion is addressed in the Congress and in industry, where many jobs are at stake. Conversion of the national laboratories, particularly nuclear weapons laboratories, has been a subject of a governmental commission and is the subject of draft legislation. Health care costs and the appropriate role of the federal government in funding basic and applied research has become a major topic of debate. Discussion on education in science has grown from the issue of how to produce more Ph.D.'s to how to improve the understanding of technology and science among the general public.

  1. Responses of wind erosion to disturbance in a desert scrub grassland: grass vs. bush cover, and a snapshot into recovery

    Science.gov (United States)

    Baddock, M.; Zobeck, T. M.; D'Odorico, P.; van Pelt, S.; Ravi, S.; Over, T. M.; Bhattachan, A.

    2010-12-01

    The mixture of grass and bush vegetation that typifies many desert scrublands is a distinctive feature of the northern Chihuahuan Desert, where it represents a change in land cover driven by shrub encroachment. In such environments, the redistribution of nutrients by aeolian transport has been recognized as an important biophysical process, with a role in sustaining shrub presence. Investigation of disturbances in these landscapes (e.g. fire and grazing) will enable better understanding of their dust emission behavior with changing climate, perturbance regime and management scenarios. Here we use a portable wind tunnel to investigate the impact of fire and animals on soil erodibilty and dust emissions from different vegetation types in the Sevilleta Wildlife Refuge, central New Mexico. Plots were selected that were a) predominantly creosote bush or b) predominantly grass covered. Dust emission was measured for these surfaces both before and after a prescribed burn was conducted. The grass plots were also clipped and artificially trampled to simulate grazing. PM10 concentrations and emission rates from the test surfaces are shown for initial blow-off experiments as the wind tunnel flow accelerates to a target velocity, plus the steady state emission flux produced under constant wind flow with an added abrader sand. An adjacent area burned 8 months previously also allowed investigation of the change in erodibility of the soil for a known time after fire. Our preliminary results indicate the extent that dust emission is changed by the introduced disturbances, and their differing effect on creosote bush and grass dominated covers.

  2. Transmissibility of Leishmania infantum from maned wolves (Chrysocyon brachyurus) and bush dogs (Speothos venaticus) to Lutzomyia longipalpis.

    Science.gov (United States)

    Mol, Juliana P S; Soave, Semíramis A; Turchetti, Andréia P; Pinheiro, Guilherme R G; Pessanha, Angela T; Malta, Marcelo C C; Tinoco, Herlandes P; Figueiredo, Luiza A; Gontijo, Nelder F; Paixão, Tatiane A; Fujiwara, Ricardo T; Santos, Renato L

    2015-09-15

    Leishmania (Leishmania) infantum is the cause of visceral leishmaniasis in the Americas. The disease is transmitted mostly through the bite of the invertebrate vector, the phlebotomine Lutzomyia longipalpis in the New World. Although the domestic dog is considered the most important reservoir of the disease, other mammalian, including wildlife, are susceptible to infection. The goal of this study was to perform xenodiagnosis to evaluate the capacity of naturally infected maned wolves (Chrysocyon brachyurus) and bush dogs (Speothos venaticus) to transmit Leishmania infantum to female sand flies (L. longipalpis). Xenodiagnoses were performed in February and August, 2013, when 77.7% (three maned wolves and four bush dogs) or 100% of the animals were positive, respectively. However, parasite loads in the engorged sand flies was low (<200 promastigotes and <150.2 parasites/μg of DNA). No statistically significant differences were observed between the two species or the two time points (February and August). In conclusion, this study demonstrated that maned wolves (C. brachyurus) and bush dogs (S. venaticus) asymptomatically infected with L. infantum are capable of transmitting L. infantum to the invertebrate host L. longipalpis, although the parasite loads in engorged phlebotomines exposed to these animals were very low.

  3. Absorption of copper(II) by creosote bush (Larrea tridentata): use of atomic and x-ray absorption spectroscopy.

    Science.gov (United States)

    Gardea-Torresdey, J L; Arteaga, S; Tiemann, K J; Chianelli, R; Pingitore, N; Mackay, W

    2001-11-01

    Larrea tridentata (creosote bush), a common North American native desert shrub, exhibits the ability to take up copper(II) ions rapidly from solution. Following hydroponic studies, U.S. Environmental Protection Agency method 200.3 was used to digest the plant samples, and flame atomic absorption spectroscopy (FAAS) was used to determine the amount of copper taken up in different parts of the plant. The amount of copper(II) found within the roots, stems, and leaves was 13.8, 1.1, and 0.6 mg/g, respectively, after the creosote bush was exposed to a 63.5-ppm copper(II) solution for 48 h. When the plant was exposed to a 635-ppm copper(II) solution, the roots, stems, and leaves contained 35.0, 10.5, and 3.8 mg/g, respectively. In addition to FAAS analysis, x-ray microfluorescence (XRMF) analysis of the plant samples provided further confirmation of copper absorption by the various plant parts. X-ray absorption spectroscopy (XAS) elucidated the oxidation state of the copper absorbed by the plants. The copper(II) absorbed from solution remained as copper(II) bound to oxygen-containing ligands within the plant samples. The results of this study indicate that creosote bush may provide a useful and novel method of removing copper(II) from contaminated soils in an environmentally friendly manner.

  4. Experimental reintroduction of the federally endangered Santa Cruz Island bush mallow (Malacothamnus fasciculatus var. nestioticus)

    Science.gov (United States)

    Wilken, D.H.; McEachern, K.

    2011-01-01

    Studies of Malacothamnus fasciculatus var. nesioticus were begun in 1995 to understand its distribution, reproductive biology and ecological requirements. After 100+ years of depredation by sheep, two known populations of fewer than 20 plants each survived in 1995. Molecular studies showed that each of the two populations was composed of 1–3 genets. During our study, two additional populations of similar size were discovered. Plants are self-compatible but require insect visitation to augment pollination. Based on seed set, viable embryos, and germination rates, we found no evidence for inbreeding depression. Bush mallow also reproduces vegetatively by rhizomes, the primary means of establishment and persistence in natural populations, and a key feature for maximizing recovery success. Ex situ observations and trial in situ outplantings suggested that supplemental watering was critical to initial survival. We developed a recovery strategy composed of four plots located at varying elevations and aspects. Each plot was enclosed to exclude feral pigs, which posed a continuing threat. Each plot was planted with twelve rooted plants derived from each of three natural populations. Plants were provided supplemental watering for four months. Survivorship after one year ranged from 46% to 91%. Significant differences in survivorship were observed relative to source of plants. After twelve months some plants were flowering and reproducing vegetatively.

  5. Analysis of Some Physio-Chemical Properties of Milk Bush (Thevetia peruviana Seeds

    Directory of Open Access Journals (Sweden)

    O.M. Olatunji

    2011-02-01

    Full Text Available The proximate and some technological properties of milk bush (Thevetia peruviana seeds were investigated. The results obtained showed the following chemical compositions: Moisture content (2.94%, protein (7.44%, oil (57.05%, crude fibre (22.37%, ash (2:24 and carbohydrate by difference (7.76%. In the same vain, mineralogical analysis using an inductively coupled plasma atomic emission spectrometer was conducted. The results obtained showed that magnesium, potassium and sodium were the predominant elements in the seeds. The technological properties studied were unit mass, unit volume, geometric mean, diameter, sphericity, bulk density, true density and porosity with average values of 4.14 g, 4.403.57 mm3, 20.34 mm, 0.67, 657.73 kg/m3, 942.05 kg/m3 and 31%, respectively. Information of these properties could be useful in process machine design. On the other hand, knowledge of the proximate properties is important for nutritional and dietary information.

  6. Effects of landscape structure on movement patterns of the flightless bush cricket Pholidoptera griseoaptera.

    Science.gov (United States)

    Diekötter, Tim; Speelmans, Marjan; Dusoulier, François; Van Wingerden, Walter K R E; Malfait, Jean-Pierre; Crist, Thomas O; Edwards, Peter J; Dietz, Hansjörg

    2007-02-01

    Because the viability of a population may depend on whether individuals can disperse, it is important for conservation planning to understand how landscape structure affects movement behavior. Some species occur in a wide range of landscapes differing greatly in structure, and the question arises of whether these species are particularly versatile in their dispersal or whether they are composed of genetically distinct populations adapted to contrasting landscapes. We performed a capture-mark-resight experiment to study movement patterns of the flightless bush cricket Pholidoptera griseoaptera (De Geer 1773) in two contrasting agricultural landscapes in France and Switzerland. The mean daily movement of P. griseoaptera was significantly higher in the landscape with patchily distributed habitat (Switzerland) than in the landscape with greater habitat connectivity (France). Net displacement rate did not differ between the two landscapes, which we attributed to the presence of more linear elements in the connected landscape, resulting in a more directed pattern of movement by P. griseoaptera. Significant differences in the movement patterns between landscapes with contrasting structure suggest important effects of landscape structure on movement and dispersal success. The possibility of varying dispersal ability within the same species needs to be studied in more detail because this may provide important information for sustainable landscape planning aimed at maintaining viable metapopulations, especially in formerly well-connected landscapes.

  7. Comparative study of Trombe wall, water wall and trans wall

    Energy Technology Data Exchange (ETDEWEB)

    Sodha, M.S.; Bansal, N.K.; Singh, S.; Ram, S.; Annamalai, M.; Iyer, M.V.; Nirmala, K.A.; Venkatesh, P.; Prasad, C.R.; Subramani, C.

    1982-01-01

    The thermal performances of three systems viz. Trombe wall: (1) without; and (2) with vents (forced air circulation), water wall and Transwall have been studied analytically interms of heat flux entering the living space (Maintained at 20/sup 0/C) corresponding to the meteriological data on January 19, 1981 at New Delhi (India), a typical cold winter day. Subsequent parametric studies using the simulation indicated that the Transwall system is the more efficient system for the passive heating of buildings.

  8. One-Terminal Fault Location for VSC-HVDC Transmission Lines Based on Principles of Parameter Identification%基于参数识别原理的VSC-HVDC输电线路单端故障定位

    Institute of Scientific and Technical Information of China (English)

    宋国兵; 李德坤; 褚旭; 饶菁; 蔡新雷

    2012-01-01

    为保障电压源换流器型直流输电(voltage source converter HVDC,VSC-HVDC)系统的可靠运行,提出一种基于参数识别原理的VSC-HVDC输电线路单端故障定位方法.由于VSC-HVDC输电线路两端并联大电容,识别故障距离的时候,在0模分量网络中可以把两端的换流站系统等效为电容,通过参数识别的原理列写出包含故障距离和过渡电阻2个未知参数的故障定位时域微分方程,通过最小二乘法优化求解该方程即可得到故障距离和过渡电阻,从而实现故障定位.PSCAD下的仿真结果表明,该方法能够实现VSC-HVDC输电线路的准确故障定位,最大测距误差不超过1%.该方法仅需要单端电气量就能实现准确故障定位,对采样频率的要求不高,理论上不受过渡电阻的影响,可以满足VSC-HVDC输电线路故障测距的要求.%To ensure reliable operation of voltage source converter HVDC (VSC-HVDC) transmission system, a one-terminal fault location method for VSC-HVDC transmission line is proposed. Because high-capacity capacitors are connected to both ends of VSC-HVDC transmission line, so during the fault location the converter station systems at both ends of VSC-HVDC transmission line can be equivalent to capacitors in the network of zero-mode component, and by means of the principle of parameter identification the differential equations in time-domain, which contains two unknown parameters of fault distance and transition resistance, can be listed, and solving this equation by least square optimization both fault distance and transition resistance can be attained, thus the fault location is implemented. The proposed method only needs single end electric quantities and is undemanding to sampling frequency, besides, theoretically this method is not affected by transition resistance, so it can meet the demand on fault location for VSC-HVDC transmission lines. Results of PSCAD simulation show that the proposed method can implement

  9. Domain Walls on Singularities

    CERN Document Server

    Halyo, Edi

    2009-01-01

    We describe domain walls that live on $A_2$ and $A_3$ singularities. The walls are BPS if the singularity is resolved and non--BPS if it is deformed and fibered. We show that these domain walls may interpolate between vacua that support monopoles and/or vortices.

  10. The Lamportian cell wall

    Energy Technology Data Exchange (ETDEWEB)

    Keiliszewski, M.; Lamport, D. (Michigan State Univ. Plant Research Lab., East Lansing (United States))

    1991-05-01

    The Lamportian Warp-Weft hypothesis suggests a cellulose-extensin interpenetrating network where extensin mechanically couples the load-bearing cellulose microfibrils in a wall matrix that is best described as a microcomposite. This model is based on data gathered from the extensin-rich walls of tomato and sycamore cell suspension culture, wherein extensin precursors are insolubilized into the wall by undefined crosslinks. The authors recent work with cell walls isolated from intact tissue as well as walls from suspension cultured cells of the graminaceous monocots maize and rice, the non-graminaceous monocot asparagus, the primitive herbaceous dicot sugar beet, and the gymnosperm Douglas Fir indicate that although extensins are ubiquitous to all plant species examined, they are not the major structural protein component of most walls examined. Amino acid analyses of intact and HF-treated walls shows a major component neither an HRGP, nor directly comparable to the glycine-rich wall proteins such as those associated with seed coat walls or the 67 mole% glycine-rich proteins cloned from petunia and soybean. Clearly, structural wall protein alternatives to extensin exist and any cell wall model must take that into account. If we assume that extracellular matrices are a priori network structures, then new Hypless' structural proteins in the maize cell wall raise questions about the sort of network these proteins create: the kinds of crosslinks involved; how they are formed; and the roles played by the small amounts of HRGPs.

  11. Halogenation of microcapsule walls

    Science.gov (United States)

    Davis, T. R.; Schaab, C. K.; Scott, J. C.

    1972-01-01

    Procedure for halogenation of confining walls of both gelatin and gelatin-phenolic resin capsules is similar to that used for microencapsulation. Ten percent halogen content renders capsule wall nonburning; any higher content enhances flame-retardant properties of selected internal phase material. Halogenation decreases permeability of wall material to encapsulated materials.

  12. Differential threshold effects of habitat fragmentation on gene flow in two widespread species of bush crickets.

    Science.gov (United States)

    Lange, Rebecca; Durka, Walter; Holzhauer, Stephanie I J; Wolters, Volkmar; Diekötter, Tim

    2010-11-01

    Effects of habitat fragmentation on genetic diversity vary among species. This may be attributed to the interacting effects of species traits and landscape structure. While widely distributed and abundant species are often considered less susceptible to fragmentation, this may be different if they are small sized and show limited dispersal. Under intensive land use, habitat fragmentation may reach thresholds at which gene flow among populations of small-sized and dispersal-limited species becomes disrupted. Here, we studied the genetic diversity of two abundant and widespread bush crickets along a gradient of habitat fragmentation in an agricultural landscape. We applied traditional (G(ST), θ) and recently developed (G'ST', D) estimators of genetic differentiation on microsatellite data from each of twelve populations of the grassland species Metrioptera roeselii and the forest-edge species Pholidoptera griseoaptera to identify thresholds of habitat fragmentation below which genetic population structure is affected. Whereas the grassland species exhibited a uniform genetic structuring (G(ST) = 0.020-0.033; D = 0.085-0.149) along the whole fragmentation gradient, the forest-edge species' genetic differentiation increased significantly from D habitat dropped below a threshold of 20% and its proximity decreased substantially at the landscape scale. The influence of fragmentation on genetic differentiation was qualitatively unaffected by the choice of estimators of genetic differentiation but quantitatively underestimated by the traditional estimators. These results indicate that even for widespread species in modern agricultural landscapes fragmentation thresholds exist at which gene flow among suitable habitat patches becomes restricted. © 2010 Blackwell Publishing Ltd.

  13. Abdominal wall fat pad biopsy

    Science.gov (United States)

    Amyloidosis - abdominal wall fat pad biopsy; Abdominal wall biopsy; Biopsy - abdominal wall fat pad ... method of taking an abdominal wall fat pad biopsy . The health care provider cleans the skin on ...

  14. Design status and procurement activities of the High Voltage Deck 1 and Bushing for the ITER Neutral Beam Injector

    Energy Technology Data Exchange (ETDEWEB)

    Boldrin, Marco, E-mail: marco.boldrin@igi.cnr.it [Consorzio RFX, Associazione EURATOM-ENEA sulla Fusione, Corso Stati Uniti 4, I-35127 Padova (Italy); De Lorenzi, Antonio [Consorzio RFX, Associazione EURATOM-ENEA sulla Fusione, Corso Stati Uniti 4, I-35127 Padova (Italy); Decamps, Hans [ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance (France); Grando, Luca [Consorzio RFX, Associazione EURATOM-ENEA sulla Fusione, Corso Stati Uniti 4, I-35127 Padova (Italy); Simon, Muriel [Fusion For Energy, c/ Josep Pla 2, 08019 Barcelona (Spain); Toigo, Vanni [Consorzio RFX, Associazione EURATOM-ENEA sulla Fusione, Corso Stati Uniti 4, I-35127 Padova (Italy)

    2013-10-15

    Highlights: ► ITER Neutral Beam Injector includes several non-standard components. ► The design status of the −1 MV{sub dc} HVD1 and Bushing is described. ► The paper reports also on the integrated layout of the two components. ► Preliminary electrostatic and thermal analyses are presented. ► Procurement activities are outlined. -- Abstract: The ITER Neutral Beam Injector (NBI) power supply system includes several non-standard components, whose ratings go beyond the present industrial practice. Two of these items, to be procured by Fusion for Energy, are: 1.A −1 MV{sub dc} air-insulated Faraday cage, called High Voltage Deck 1 (HVD1), hosting the Ion Source and Extractor Power Supplies (ISEPS) and the associated diagnostics. 2.A −1 MV{sub dc} feedthrough, called HVD1-TL Bushing, aimed at connecting the HVD1 to the gas (SF{sub 6}) insulated Transmission Line (TL), containing inside its High Voltage (HV) conductor all ISEPS power and control cables coming from the HVD1 to be connected to the NBI Ion Source services. The paper deals with the status of the design of the HVD1 and HVD1-TL Bushing, focusing on insulation, mechanical and thermal issues as well as on their integration with the other components of the power supply system. In particular, the insulation issue of the integrated system has been addressed by means of an electrostatic Finite Element (FE) analysis whilst a FE thermal simulation has been carried out to assess the impact of the dissipation of the proposed design of the inner conductors (ISEPS conductors) not actively cooled. Finally, the paper describes the status of procurement strategy and execution.

  15. 轻型高压直流输电技术的发展与展望%DEVELOPMENT AND PROSPECTS FOR HVDC LIGHT

    Institute of Scientific and Technical Information of China (English)

    李庚银; 吕鹏飞; 李广凯; 周明

    2003-01-01

    介绍了在原有高压直流输电(HVDC)基础上,以电压源换流器和绝缘栅双极晶体管为主要部件发展起来的轻型HVDC技术,分析了轻型HVDC的基本原理和技术特点,比较了轻型HVDC与传统HVDC之间的区别,简要介绍了轻型HVDC在国外的一些工程应用以及我国的研究现状,并指出目前的主要研究领域,展望了其发展前景.

  16. Neural Network Based Fault Diagnosis in HVDC System%基于神经网络的HVDC系统故障诊断

    Institute of Scientific and Technical Information of China (English)

    张家奇; 吴坚; 于飞

    2006-01-01

    HVDC(高压直流输电)系统对运行时的稳定性要求比较严格,出现故障时要求能及时分辨故障类型并快速恢复.鉴于神经网络具有很强的非线性分类能力,该文研究了多种不同结构的神经网络在HVDC系统故障诊断中的应用,并对其诊断性能进行了分析.仿真结果表明,神经网络能够很好的完成HVDC系统的故障诊断.

  17. 论高压直流输电系统的稳定性%Discussion on the Stability of HVDC System

    Institute of Scientific and Technical Information of China (English)

    张爱华

    2013-01-01

    高压直流输电(HVDC)系统与交流输电方式、UPS系统相比都具有不可比拟的优势,因此它的应用越来越普遍.但是在HVDC系统的运行过程中,存在直流偏磁、谐波等问题,这些问题都会影响HVDC的稳定性,从而给HVDC系统的正常运行造成影响.文中以交流与直流系统关系为前提,研究了影响HVDC的各项因素并提出了相应的解决方法.

  18. Liquid Wall Chambers

    Energy Technology Data Exchange (ETDEWEB)

    Meier, W R

    2011-02-24

    The key feature of liquid wall chambers is the use of a renewable liquid layer to protect chamber structures from target emissions. Two primary options have been proposed and studied: wetted wall chambers and thick liquid wall (TLW) chambers. With wetted wall designs, a thin layer of liquid shields the structural first wall from short ranged target emissions (x-rays, ions and debris) but not neutrons. Various schemes have been proposed to establish and renew the liquid layer between shots including flow-guiding porous fabrics (e.g., Osiris, HIBALL), porous rigid structures (Prometheus) and thin film flows (KOYO). The thin liquid layer can be the tritium breeding material (e.g., flibe, PbLi, or Li) or another liquid metal such as Pb. TLWs use liquid jets injected by stationary or oscillating nozzles to form a neutronically thick layer (typically with an effective thickness of {approx}50 cm) of liquid between the target and first structural wall. In addition to absorbing short ranged emissions, the thick liquid layer degrades the neutron flux and energy reaching the first wall, typically by {approx}10 x x, so that steel walls can survive for the life of the plant ({approx}30-60 yrs). The thick liquid serves as the primary coolant and tritium breeding material (most recent designs use flibe, but the earliest concepts used Li). In essence, the TLW places the fusion blanket inside the first wall instead of behind the first wall.

  19. A review of bush dog Speothos venaticus (Lund, 1842 (Carnivora, Canidae occurrences in Paraná state, subtropical Brazil

    Directory of Open Access Journals (Sweden)

    L. M. Tiepolo

    Full Text Available Abstract We report six new occurrence records of the bush dog Speothos venaticus, a widely distributed South American carnivore that is threatened with extinction. These records are accompanied by notes on the places where the records were made, such as vegetation type, date and information about the protection of areas. The records, obtained over the last 17 years in Paraná state, southern Brazil, offer an improved understanding of the species geographic range and the threats it faces and can enable better assessments of the conservation status of the species in southern Brazil.

  20. Solar heating wall

    Energy Technology Data Exchange (ETDEWEB)

    Schoenfelder, J.L.

    1983-08-16

    A solar heating wall is disclosed including a water pipe circulation system having a plurality of separate tubes, each formed as a loop, connected between a water supply and a return. The separate tubes are arranged in a single vertical plane at the approximate center of the wall. The wall is formed within a frame which is packed with a material suited for use as a thERMAL RESERVOIR, SUCH AS concrete. The frame provides extra support by having a series of horizontally disposed cross supports on one surface of the wall and a series of vertically disposed cross supports on the opposite surface A pressure relief valve may be provided between the water supply to the separate tubes and the water supply to the building or structure containing the solar wall, so that the solar wall can be adapted for use with a city water system.