Nadel, L.A.; Lint, M.G.; Ribel, N.E.
An equipment set for protection of 500+ kV power autotransformers has been developed. The entire equipment is contained in three cabinets. The first cabinet Sh2101 houses differential protection of an autotransformer and of its low-voltage busbars, one or two (depending on the voltage class) lead high-voltage insulation testers, protective devices for two-phase operation, circuits for automatic acceleration of backup action, overload relays, an alarm circuit signaling a short to ground on the low-voltage side, and tripping circuits. The second cabinet Sh2102 houses two 2-step distance relays and two directional zero-sequence current relays, one of each kind for the low-voltage side and another for the intermediate-voltage side, and circuits for manual acceleration of backup action. The third cabinet Sh2103 houses backup differential protection of an autotransformer as well as of its high-voltage and intermediate-voltage busbars, peak-current relays with holding elements for the low-voltage side, protection of the reactive branch on the low-voltage side, gas-leak protection circuitry, and tripping circuits. Reliability of the entire equipment is ensured by continuous operational monitoring of all meters and periodic spot-check testing of each cabinet, with appropriate logic and interlocking.
Full Text Available This paper focuses to 3/9 phase auto-transformer with multiple windings per phase is powered a 9-phase AC to DC converter this type of transformer has 40o phase shift between the output voltages, it is supplied from a three phase AC source with star or delta connection, to use this type of transformer in aerospace the operation frequency should be at 400Hz in addition to reduce the current harmonic distortion through a three phase line reactor are connected after three phase AC source in this case the current harmonic distortion decreases to value less than 5% and it can be less than 3% level by using an additional suppression devices (Chokes at the output of the converter, this autotransformer includes three sections each spaced 120o electrically apart. Each section comprises a main winding and a pair of phase shift windings, it is a main element in 18 pulse converters, the multiphase rectification can be analyzed by using orcad simulation software, and shown the comparisons between the odd phases so that the 9 phases has a lower value of the ripple factor which is 0.763 %.
Full Text Available This article deals with a description of methods of an experimental analysis concerning the actual condition of windings and magnetic circuit of the autotransformer, which is required in power transmission companies all over the world.
Xiao-qiang, Chen; Hao, Qiu
In this paper, a zigzag connected autotransformer-based 24-pulse AC-DC converter is designed, modeled and simulated to feed direct torque controlled induction motor drives. Winding arrangements and parameters of the autotransformer and interphase reactor are given. Moreover, the design procedure of the autotransformer is modified to make it suitable for retrofit applications. Simulation results indicate that the system is capable of eliminating up to 21st harmonics in the ac mains current. The effect of load variation and load character is also studied to demonstrate the performance and effectiveness of the proposed 24-pulse converters. A set of power quality indices at ac mains and dc side are presented to compare the performance of 6-, 12- and 24-pulse converters.
Siwakoti, Yam Prasad; Blaabjerg, Frede; Loh, Poh Chiang
This paper introduces a new single-switch nonisolated dc-dc converter with very high voltage transfer ratio and reduced semiconductor voltage stress. The converter utilizes an integrated autotransformer and a coupled inductor on the same core to achieve a high step-up voltage gain without extreme...... to use a low voltage and low RDS-on MOSFET, which reduces the cost, and also the conduction and turn on losses of the switch. The principle of operation and theoretical analysis supported by key simulation and experimental waveforms are presented in details....
Full Text Available the base of earlier proposed model calculations were made and were investigated peculiarities of special asymmetric modes of three-phase three legs autotransformer (AT with tertiary winding, connected in triangle. Calculations were carried out taking into account the electromagnetic coupling of coils, located on different legs. Modules and angles of currents and voltages vectors in autotransformer windings were calculated at breakage of one of the phases of the supply voltage and its simultaneous fault to ground at the side of AT. Based on these data vector diagrams were constructed, which give a visual representation of specific features of such regimes. Considered mode at grounded neutral is characterized by the occurrence of significant currents of the same value in all windings, app. equal to nominal current. Voltage of the windings varies slightly from the nominal values, except for the short-circuited phase. Furthermore, there is a considerable flow of the zero sequence flux, which may lead to additional heating of AT. At ungrounded neutral in this particular mode and absence of load on the secondary AT side, only a small magnetizing currents flows and neutral is significantly displaced. If the load is present, despite of the absence of the current in the neutral, currents in the windings, comparable with the nominal one appeared, also zero sequence flux appeared. In the general case, the currents of this failure (as in the previous case are much smaller, than the usual short-circuit currents, so are insufficient to trigger the relay protection, this may require additional measures to protect AT against such damage.
This paper presents a pulse doubling technique in a 12-pulse ac-dc converter which supplies direct torque controlled motor drives (DTCIMDs) in order to have better power quality conditions at the point of common coupling. The proposed technique increases the number of rectification pulses without significant changes in the installations and yields in harmonic reduction in both ac and dc sides. The 12-pulse rectified output voltage is accomplished via two paralleled six-pulse acdc converters each of them consisting of three-phase diode bridge rectifiers. An autotransformer is designed to supply the rectifiers. The design procedure of magnetics is in a way such that makes it suitable for retrofit applications where a six-pulse diode bridge rectifier is being utilized. Independent operation of paralleled diode-bridge rectifiers, i.e. dc-ripple re-injection methodology, requires a Zero Sequence Blocking Transformer (ZSBT). Finally, a tapped interphase reactor is connected at the output of ZSBT to double the pulse numbers of output voltage up to 24 pulses. The aforementioned structure improves power quality criteria at ac mains and makes them consistent with the IEEE-519 standard requirements for varying loads. Furthermore, near unity power factor is obtained for a wide range of DTCIMD operation. A comparison is made between 6-pulse, 12-pulse, and proposed converters from view point of power quality indices. Results show that input current total harmonic distortion (THD) is less than 5% for the proposed topology at various loads.
文中基于自耦变压器零序电流的分布特点,探讨了自耦变压器零序电流保护的构成及整定原则,重点分析了自耦变压器零序差动保护。%Based on zero-sequence current distributed characteristics of auto-transformer,the construction and setting principle of zero-sequence current protection is discussed in this paper.Particularly analyses zero-sequence current different protection of auto-transformer.
P. Shyam Kiran
Full Text Available In this paper, a new voltage sag compensator for critical loads in electrical distribution system discussed. The proposed scheme employs a Pulse width modulation ac-ac converter along with a auto transformer. During a disturbance such as voltage sag, the proposed scheme supplies the missing voltage and helps in maintaining the rated voltage at the terminals of the critical load. Under normal condition the approach work in bypass mode and delivering utility power directly to load. The proposed system has less number of switching devices and has good compensating capability in comparison to commonly used compensators. Simulation analysis of three-phase compensator is performed in MATLAB/SIMULINK and performance analysis of the system is presented for various levels of sag and swell.
Methods of increasing the operating reliability of power transformers, autotransformers and shunting reactors in order to reduce the risk of damage, which accompany internal short circuits and equipment fires and explosions, are considered
The radiational-thermal development of coil short circuits due to the action of partial discharges of the first kind when the windings of transformers, autotransformers and shunting reactors become contaminated with metal-containing colloidal particles, formed in the transformer oil as a result of the interaction of the oil with the constructional materials (the copper of the windings, the iron of the tank, the core etc.) is considered. Acriterion of dangerous contamination of the coil insulation of the windings by metal-containing colloidal particles is proposed, namely, 3% of the mass content of copper and iron in it, which, if exceeded, may serve as a basis for recognizing the state of transformers, autotransformers and shunting reactors at a voltage of 110 kV and above the limit. It is shown that filters for continuously cleaning the oil play a considerable role in prolonging the life of transformer equipment.
This paper is concerned with a monitoring and diagnostics system currently in operation for a high power autotransformer and is associated bays. The diagnostics system analyses and crosschecks in a statistical way all the recorded data and diagnostic indicators (voltages, currents, pressures, temperatures, dissolved gases, alarms, controls and positions), increasing the quality and the amount of the technical information available to maintenance personnel. The system prototype is divided into two separate units, communicating via a fiber optic link, which are permanently installed, the latter near the autotransformer. The data processing unit is based upon a VME Bus and is made up of a data acquisition system, an on-line processor and an off-line CPU. During the system design, care was taken not only to avoid environmental as well as EMC troubles, but also to prevent disturbing the operation of the transformer bay itself and the connected equipment
Oliveira, Jose Carlos de; Guimaraes, Geraldo Caixeta; Moraes, Adelio Jose [Uberlandia Univ., MG (Brazil); Abreu, Jose Policarpo G. de [Escola Federal de Engenharia de Itajuba, MG (Brazil); Oliveira, Edimar Jose de [Juiz de Fora Univ., MG (Brazil)
This article aims to present initially the constructive and operative forms of a phase-shift autotransformer which provides both magnitude and phase angle change through thyristor commutation, including a technic to reduce the number of thyristors. Following, it is proposed a control system to make such equipment an efficient AC system stabilizing tool. It is presented some simulation results to show the operation of this transformer in an electrical system. (author) 3 refs., 11 figs., 3 tabs.
Griffo, Antonio; Wang, J B; Howe, D.
The paper presents an averaged-value model of the direct symmetric topology of 18-pulse autotransformer AC-DC rectifiers. The model captures the key features of the dynamic characteristics of the rectifiers, while being time invariant and computationally efficient. The developed models, validated by comparison of the resultant transient and steady state behaviours with those obtained from detailed simulations can, therefore, be used for stability assessment of electric power syste...
A control system has been developed for the energy control of the electron beam accelerator using PLC. The accelerating voltage of 3 MV has been obtained by using parallel coupled voltage multiplier circuit. A autotransformer controlled variable 0-10 KV DC is fed to a tube based push pull oscillator to generate 120 Khz, 10 KV AC. Oscillator output voltage is stepped up to 0-300 KV/AC using a transformer. 0-300 KVAC is fed to the voltage multiplier column to generate the accelerating voltage at the dome 0-3 MV/DC. The control system has been designed to maintain the accelerator voltage same throughout the operation by adjusting the input voltage in close loop. Whenever there is any change in the output voltage either because of beam loading or arcing in the accelerator. The instantaneous accelerator voltage or energy is a direct proportional to 0-10 KVDC obtained from autotransformer. A PLC based control system with user settable energy level has been installed for 3 MeV, EB accelerator. The PLC takes the user defined energy value through a touch screen and compares it to the actual accelerating voltage (obtained using resistive divider). Depending upon the error the PLC generates the pulses to adjust the autotransformer to bring the actual voltage to the set value within the window of error (presently set to +/- 0.1%). (author)
Singh, Bim; Bhuvaneswari, G.; Garg, Vipin [Indian Inst. of Technology, Dept. of Electrical Engineering, New Delhi (India)
This paper presents an optimised 12-pulse autotransformer-based AC-DC converter with reduced kVA magnetics for reducing the harmonic distortion in AC mains current in a vector-controlled induction motor drive (VCIMD). The proposed AC-DC converter results in elimination of fifth, seventh and 11th harmonics in the supply current. The proposed system consists of an autotransformer and a tuned passive filter. A small rating passive filter is tuned to 11th harmonic frequency and it reduces the harmonic currents generated by the AC-DC converter, thus reducing the total harmonic distortion of AC mains current. The filter is tuned such that the supply current is less than the converter input AC current. The detailed simulations of the drive system along with the 12-pulse AC-DC converter are carried out in MATLAB environment using SIMULINK and power system blockset toolboxes. Four different topologies of 12-pulse autotransformer connections have been considered to feed voltage source inverter-based VCIMD. A set of power quality parameters such as total harmonic distortion and crest factor of AC mains current, power factor, displacement factor and distortion factor at AC mains and DC bus ripple factor for a VCIMD fed from different 12-pulse converters are computed and tabulated. The effect of load on VCIMD is also studied to demonstrate the effectiveness of the proposed topology for power quality improvement of AC mains. (Author)
Full Text Available The location of ground faults in railway electric lines in 2 × 5 kV railway power supply systems is a difficult task. In both 1 × 25 kV and transmission power systems it is common practice to use distance protection relays to clear ground faults and localize their positions. However, in the particular case of this 2 × 25 kV system, due to the widespread use of autotransformers, the relation between the distance and the impedance seen by the distance protection relays is not linear and therefore the location is not accurate enough. This paper presents a simple and economical method to identify the subsection between autotransformers and the conductor (catenary or feeder where the ground fault is happening. This method is based on the comparison of the angle between the current and the voltage of the positive terminal in each autotransformer. Consequently, after the identification of the subsection and the conductor with the ground defect, only the subsection where the ground fault is present will be quickly removed from service, with the minimum effect on rail traffic. This method has been validated through computer simulations and laboratory tests with positive results.
Yao, Wenli; Blaabjerg, Frede; Zhang, Xiaobin;
The power electronics technology plays an even more important role in the aerospace applications of More Electric Aircrafts (MEA). AutoTransformer Rectifier Units (ATRU) have been widely adopted in aircrafts due to its simplicity and reliability. In this paper, Zero Sequence Blocking Transformers...... and cost of the entire system. The operation principle of the ZSBT is analyzed, and the kVA rating design of each component in the proposed unit is also explored. The kVA rating of ZSBT is only 0.034 times of the rated power. Moreover, this topology can eliminate low-order harmonics in the AC supply...
Raposa, F. L. (Inventor)
A self-stabilizing voltage regulator is described. Direct current voltage regulation employing a series transistor rendered conductive during various portions of a cycle is controlled by saturation of an autotransformer. The constant volt-second capacity of the transformer provides conduction time inverse to the input voltage whereby average output voltage is maintained constant. Conduction commenced in response to short gate signals, and resistor feedback for degenerative turn-off of the transistor was after transformer saturation. Standard output filters are also included.
Jesus Serrano; Platero, Carlos A.; Maximo López-Toledo; Ricardo Granizo
The location of ground faults in railway electric lines in 2 × 5 kV railway power supply systems is a difficult task. In both 1 × 25 kV and transmission power systems it is common practice to use distance protection relays to clear ground faults and localize their positions. However, in the particular case of this 2 × 25 kV system, due to the widespread use of autotransformers, the relation between the distance and the impedance seen by the distance protection relays is not linear and therefo...
Shneerson, E.M.; Fedorov, E.K.; Virt, A.N.
The already commercially produced protective distance relaying equipment of the latest design includes PDE 2001 panel replacing the DZ-503 panel for 500-750 kV transmission lines, ShDE 2801/2 cabinets replacing EPZ-1636 and PZ-201 panels, module BRE 2801 of impedance relays replacing KRS-2/3 sets, and module BRE 2701 of distance relays replacing the PZ-3 set for protection against any kind of short-circuit along 10-35 kV transmission lines, also a set of distance relays in the Sh2102 cabinet for protection of 330 kV autotransformers. Any of these new 3-step distance relays is designed for any kind of interphase short-circuit. The panels and the cabinets are designed to coordinate the operation of all protective relaying devices by proper interconnection and circuit matching, with inclusion of necessary reserve capacity.
Siwakoti, Yam Prasad; Blaabjerg, Frede; Galigekere, Veda Prakash;
A novel A-source impedance network is proposed in this letter. The A-source impedance network uses an autotransformer for realizing converters for any application that demand a very high dc voltage gain. The network utilizes a minimal turns ratio compared to other Magnetically Coupled Impedance...... Source (MCIS) networks to attain a high voltage gain. In addition, the proposed converter draws a continuous current from the source, and hence it is suitable for many types of renewable energy sources. The derived network expressions and theoretical analysis are finally validated experimentally...... with an example single-switch 400 W dc-dc converter. For the closed-loop control design and stability assessment, a small signal model and its analysis of the proposed network are also presented in brief....
Wiechowski, Wojciech Tomasz
, provided that background harmonic distortion, and the network configuration, are not changing during the measurement. It is shown that switching of a shunt linear power system component can result in variation of the harmonic levels that can be measured and used to verify the harmonic model of the network......, in order to determine which power system component, when switched, results in the largest change in harmonic levels, some initial harmonic simulations, using the created harmonic model of Energinet.dk transmission network, are performed. The criterion is that the measuring equipment shall not be installed...... of the measurements. The conclusion is that a key requirement of this technique is a good synchronization of the measurements. Capacitive voltage transformers installed at the 400 kV substations are not suited to measure higher frequencies and the capacitive taps of the 400 kV/150 kV autotransformer bushings are used...
In much pulsed power experimentation a capacitor bank is discharged into an inductive load, but although sufficient energy may be available in the capacitors their voltage rating may considerably exceed that necessary for the load and the current delivered during the experiment may accordingly be too low. This paper describes a novel design of air-cored transformer that has been used as an interfacing or matching device in such a situation, where peak load currents between 1 and 2 MA were required. Design considerations led to the use of an air-cored autotransformer connection wound with copper sheet conductors. Although thick wide conductors and clamping are needed to prevent deformation due to high magnetic pressure, the transformer is nevertheless relatively simple, easy to make, lightweight and inexpensive. This paper describes the design and the winding arrangement of the transformer that was constructed, and presents typical experimental results
Lee, F. C.; Cho, B. H.
The progress to date on the analysis and design of a high power, digitally controlled spacecraft power system is described. Several battery discharger topologies were compared for use in the space platform application. Updated information has been provided on the battery voltage specification. Initially it was thought to be in the 30 to 40 V range. It is now specified to be 53 V to 84 V. This eliminated the tapped-boost and the current-fed auto-transformer converters from consideration. After consultations with NASA, it was decided to trade-off the following topologies: (1) boost converter; (2) multi-module, multi-phase boost converter; and (3) voltage-fed push-pull with auto-transformer. A non-linear design optimization software tool was employed to facilitate an objective comparison. Non-linear design optimization insures that the best design of each topology is compared. The results indicate that a four-module, boost converter with each module operating 90 degrees out of phase is the optimum converter for the space platform. Large-signal and small-signal models were generated for the shunt, charger, discharger, battery, and the mode controller. The models were first tested individually according to the space platform power system specifications supplied by NASA. The effect of battery voltage imbalance on parallel dischargers was investigated with respect to dc and small-signal responses. Similarly, the effects of paralleling dischargers and chargers were also investigated. A solar array and shunt model was included in these simulations. A model for the bus mode controller (power control unit) was also developed to interface the Orbital replacement Unit (ORU) model to the platform power system. Small signal models were used to generate the bus impedance plots in the various operating modes. The large signal models were integrated into a system model, and time domain simulations were performed to verify bus regulation during mode transitions. Some changes have
Petrov, A.A.; Karkazov, E.I.
While the RVA-62 automatic field-current regulator performs adequately with small and medium-size turbogenerators, its stability margin being often sufficiently large to compensate design inaccuracies, a refinement is nevertheless recommended to ensure reliability under no-load as well as during parallel operation of generators into a common busbar group. The procedure is based on necessary adjustments of over 40 units and applies to redesign, measurements, breadboard simulation, settings, reassembly, and testing. First it is necessary to determine the correct number of primary and secondary turns in the universal controlled phase-compounding transformer, taking into account the parameters of associated equipment (autotransformer, filter choke, power rectifier, current transformer) as well as various modes of generator instability and the use of automatic field suppression. Revisions in testing circuitry and procedure are proposed, including more precise and some extra measurements, also replacement of selenium rectifiers with silicon diodes. Adjustments according to this scheme have been made in the RVA-62 regulators for 6-60 kW generators with VT exciters and 3000-12,000 kW generators, including Skoda, Siemens-Schuckert GmbH, Parsons Ltd units.
Bogatyrev N. I.
Full Text Available The article contain the peculiarities of testing asynchronous generator with sixzone winding on the basis of the asynchronous motor series 4A100S4 and analysis of obtained characteristics. Circuit parameters of the stator winding can significantly affect the characteristics of the asynchronous generator. Asynchronous generator was tested with a stator winding connected star, autotransformer and sectional winding. Use chastising windings opens the possibility of applying various circuits of capacitors and the load to asynchronous generators, which in turn affect the efficiency and stabilizing properties of the electric machine. Asynchronous generators to test with sectional winding by confirmation of theoretical calculations for determine the most optimal scheme under connect capacitors and load, testing the stator winding. The volume of testing for asynchronous generators standard is not defined, so we proposed testing method, taking into account the design features of the stator winding. Asynchronous generators were tested with the help of special equipment with the use of analyzer of energy power quality. Article contains characteristics of idling, short circuit and others, considered the heat mode. On the basis of the results we have determined the parameters of the circuit, the efficiency and power factor of induction generator
Liu, Y.L. [Institute of Materials Physics and Chemistry, School of Sciences, Northeastern University, Shenyang 110819 (China); Shahzad, M. Babar [Institute of Materials Physics and Chemistry, School of Sciences, Northeastern University, Shenyang 110819 (China); Institute of Metals Research, Chinese Academy of Sciences, Shenyang 110016 (China); Qi, Y., E-mail: email@example.com [Institute of Materials Physics and Chemistry, School of Sciences, Northeastern University, Shenyang 110819 (China)
Highlights: • The O/Zn effect on the non-polar a-axis film growth is studied at the atomic scale. • The optimized film quality is achieved through a series of ReaxFF based MD study. • A film growth mode (singular atom → cluster → chains → continue film) is revealed. • The transformed way of the defective substrate to the perfect stacking is revealed. - Abstract: The understanding of the growth process and formation mechanism of non-polar ZnO films in atomic-scale is crucial in adjusting and controlling the film deposition conditions. Using the advanced reactive force field based molecular dynamics method, we theoretically studied the effect of O/Zn ratios (8/10–10/8) on the quality of ZnO films. The comprehensive investigation of energy and temperature fluctuation profile, radial distribution function, the sputtering and injecting phenomenon, and layer coverage indicated that the film grown under stoichiometric conditions possesses the optimized quality. Furthermore, the auto-transformation ability of the substrate from defective to perfect stacking was presented and discussed by comparing to the perfect structure. The instant film growth configurations, atomic layer snapshots, and the interfacial morphology evolution were provided step-by-step to reveal the defect type and initial film nucleation and growth mechanism.
Robles Balestero, Juan Paulo; Lessa Tofoli, Fernando; Mendes de Seixas, Claudiner; Torrico Bascopé, Grover Victor; José Mendes de Seixas, Falcondes
This article presents a comparative study involving a buck converter derived from the three-state switching cell in both operation modes, i.e. non-overlapping and overlapping modes, since it is well known in literature that several advantages can be addressed to topologies based on this approach. In the case of the mentioned converter, only part of the load delivered to the load flows through the controlled switches, so that operation at high-current high-power levels is possible. Besides, the design of reactive elements such as very autotransformer and filter inductor is performed for twice the switching frequency, with consequent reduction of size, weight and volume. Another clear advantage is that the area for which the converter operates in continuous conduction mode is wider than that for the discontinuous conduction mode in comparison with the so-called classical non-isolated buck converter. The operation of the converter, which was previously proposed in literature, is analysed considering the aforementioned modes in terms of the efficiency, and similar approaches for the non-isolated dc-dc conversion are also investigated.
The elaboration of a study of transient stability is seen as part of the planning process associated with the Plan de Expansion de la Transmision. Studies have historically contemplated the calculation of critics times of release of failures without allowing to obtain conclusive information about the performance of protection systems. An evaluation of the protection schemes of substations is determined make of the Sistema Nacional Interconectado of year 2014. Analysis of transient stability was used to verify compliance with the ''Criterios de Seguridad para la Planificacion, Diseno y Operacion del Sistema Electrico Nacional'' and ''Criterios de Calidad, Seguridad y Desempeno'' of the Reglamento del Mercado Electrico Regional in order to determine the necessary improvements. A methodology is proposed for simulating the behavior of protection systems using the software PSS/E, which has replaced the methodology based on the calculation of critical times. The presence of 42 substations were determined in which the release of failures for remote backup has caused unstable conditions of the system. 174 improvements have identified as necessary among which are: the implementation of distance relays in autotransformers, differential protections in reactors, differentials of lines and overcurrents of definite time in lines, duplication of differentials in bars, the replacement of pole breakers for monopolar and duplication of breakers of link bars. The current criteria have been recommended to supplement with probabilistic criteria to avoid incurring unnecessary investments. (author)
In the transformer rectifier circuit, unbalance of the output voltage of the device is quite large, so the analysis input voltage imbalance on the output voltage is very important. This article wil be a quantitative analysis of isolation transformers and autotransformers asymmetries and imbalances affect the input volt-age of the rectifier system, through data analysis to a detailed analysis of the relationship between different parameters of transformer voltage imbalance.%在变压器整流电路中，输出电压的不平衡对设备的影响是是相当大的，因此分析输入电压不平衡对输出电压的影响是非常重要的。在本文中将定量的分析隔离式变压器和自耦变压器不对称和输入电压不平衡对整流系统的影响，通过数据分析来详细的分析不同变压器参数与电压不平衡的关系。
SPHINX is a microsecond linear transformer driver located at Atomic Energy Commission (CEA) Gramat (France), which can deliver a current pulse of 6 MA within 800 ns in a Z-pinch load. Using the concept of the dynamic load current multiplier (DLCM), which was proposed by Chuvatin, we expect to increase the load current above 6 MA, while decreasing its rise time to ∼300 ns. The DLCM developed by the CEA Gramat and International Technologies for High Pulsed Power (ITHPP) is a compact system made up of concentric electrodes (auto-transformer), a dynamic flux extruder (cylindrical wire array), a vacuum convolute (eight post-hole rods), and a closing switch (compact vacuum surface switch). The latter is a key component of the system, which is used to prevent the current from flowing into the load until the inductance builds up due to the implosion of the wire array. This paper presents the design and testing of the DLCM surface switch, resulting from both electrostatic simulations and experiments on the SPHINX generator. These studies, carried out either with or without load (open circuit), were valuable for a first experimental evaluation of the DLCM scheme in a microsecond regime and provided detailed information on the surface switch behavior. (authors)
Innovation of high voltage supply adjustment device on diagnostic x-ray machine has been carried out. The innovation is conducted by utilizing an electronic circuit as a high voltage adjustment device. Usually a diagnostic x-ray machine utilizes a transformer or an auto-transformer as a high voltage supply adjustment device. A high power diagnostic x-ray machine needs a high power transformer which has big physical dimension. Therefore a box control where the transformer is located has to have big physical dimension. Besides, the price of the transformer is expensive and hardly found in local markets. In this innovation, the transformer is replaced by an electronic circuit. The main component of the electronic circuit is Triac BTA-40. As adjustment device, the triac is controlled by a variable resistor which is coupled by a stepper motor. A step movement of stepper motor varies a value of resistor. The resistor value determines the triac gate voltage. Furthermore the triac will open according to the value of electrical current flowing to the gate. When the gate is open, electrical voltage and current will flow from cathode to anode of the triac. The value of these electrical voltage and current depend on gate open condition. Then this triac output voltage is feed to diagnostic x-ray machine high voltage supply. Therefore the high voltage value of diagnostic x-ray machine is adjusted by the output voltage of the electronic circuit. By using this electronic circuit, the physical dimension of diagnostic x-ray machine box control and the price of the equipment can be reduced. (author)
XishanHao; BaocunSun; ShiwuZhang; XiulanZhao
OBJECTIVE To determine if vasculogenic mimicry (VM) exists in bi-directional differentiated malignant tumors. METHODS The blood supply models for bi-directional differentiated tumors were studied with immunohistochemical and PAS double-staining techniques. New sections were made from 158 paraffin-embedded bi-directional malignant-tumor samples, including melanoma (high malignancy n=30, low malignancy n=30); synoviosarcoma(SS) (high malignancy n=26, low malignancy n=13); acinar rhabdomyosarcoma (All) (high malignancy n=16,low malignancy n=13); malignant mesothelioma (MM) (n=26), and epithelioid sarcoma (ES)(n=4). Tissue microarrays were made. The representative points in the paraffin sections were labeled and two tissue microarrays were made, one included 60 cases of melanoma, and the other included the other tumors. Immunohistochemical staining of the platelet-endothelial cell adhesive molecule(CD31 antigen) and periodic acid Schiff(PAS) staining were conducted. The areas were calculated of vessel-like channels consisting of CD31 antigen-positive tumor cells and of PAS positive materials. The VM was studied using the data obtained. RESULTS Some of these bi-directional tumor cells secreted PAS-positive materials and 0D31 positive materials. The walls of the VM consisted of PAS-positive materials lined with CD31 negative tumor cells with red blood cells inside the channel, whereas the walls of the epithelium-dependent vessels were comprised of CD31 positive materials. The positive areas of CD31 were significantly less than that of PAS (P<0.01). The number of cases with VM in highly malignant tumors was greater than that found in the lowly malignant tumors. CONCLUSIONS Bi-directional differentiated malignant tumor cells have the ability to auto-transform and might interact with the extracellular matrix to form a vessel channel system which mimics blood vessels for transporting blood. That process is called VM. Results in this study show that bi
The extensive use of non-linear and electronically switched loads in power system has lead to higher incidences of harmonic distortion of the voltage and current waveforms. Harmonic currents degrade power quality and are considered the main source of many system malfunctions. Technical guidelines and standards regarding suppressions of system harmonic contents have been enacted. This dissertation proposes several new three-phase power factor correction (PFC) schemes using single-phase PFC modules. An integrated single-switch approach is first proposed. This is essentially an add-on solution to standard ASD's. This approach is based on circulating third harmonic current between neutral and DC mid-point by utilizing a lossless resistor. Single-phase PFC emulates this resistor to control the amplitude of the current, which is implemented by the dynamic breaking chopper available in standard adjustable speed drives (ASD's). This approach is also capable of reducing harmonic distortion in multiple drives. Analysis, design and simulations are conducted to determine the performance of the proposed scheme with different line impedances and with and without dc-link inductance in the ASD. Experimental results are presented using commercial ASD retrofitted with the proposed approach. Second scheme proposes a three-phase PFC using two standard single-phase PFC modules. In this approach, three-phase input is transformed into two-phase by means of 0.14 pu autotransformer. Two standard single-phase PFC modules are employed to process two-phase power to do output. Split inductors and diodes are employed to limit the interaction between the two phases. A method to eliminate the interaction between phases is also described. Due to cascade operation of two PFC stages, low frequency (120Hz) ripple in dc-link is cancelled. An active interphase transformer (IPT) scheme is proposed to draw sinusoidal input line currents, in the third study. This scheme utilizes a unique combination of a
access to international connections, contractual exchanges by border; and the evolution of the transmission network - the following facilities were commissioned on the RTE network in July 2003: A 600 MVA auto-transformer at the 400 kV Tricastin substation; the Tricastin substation has also been connected to the 225 kV Bollene-Chateauneuf du Rhone 1 line, as part of work to restructure the 225 kV network between Tavel and Tricastin; Transformer 632 at the 225 kV Bruges substation, for strengthening supply to the Bordeaux area; Transformer 612 at the Muette substation, for relieving pressure on the 225 kV lines circling Paris; the 63 kV substation at Arsot, connected to the substation at Argiesans by a 9.6 km underground cable; the 63 kV Cissac-Margaux line, following the connection of the Margaux substation to the 63 kV Bruges-Cissac 1 line. (A.L.B.)