Proceedings - International Symposium on Discharges and Electrical Insulation in Vacuum, ISDEIV

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  • ISSN
    1093-2941

Publications in this journal

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    ABSTRACT: Compactness of switchgear can be reached using a shielded solid insulation technology. Thus the size and costs can be reduced and the substation installation becomes easier and more attractive for customers. Constraints are then reported on the design of Vacuum Circuit Breaker in order to fulfill the whole standard requirements. A new embedded Vacuum Interrupter was developed that complies with requirements related to partial discharges, thermal cycles, mechanical endurance, breaking performance and disconnecting dielectric withstand. Multi-physics simulations were widely used to match industrial and technical requirements of such a complex system. For instance, overmolding simulation is mandatory to ensure the material homogeneity, the suitability of stresses with thermal constraints and that there are no holes. Radial Magnetic Field contacts were used to get compactness, cost effectiveness and breaking capacity. Contact material was also selected in order to obtain the best compromise between breaking performance, anti-welding property and low erosion. Thus the E2 electrical endurance class and 50 full interruptions at 25kA/15kV were achieved with less than 0.8mm erosion. No degradation of power frequency dielectric performance across isolating distance was found after breaking tests. Finally, this vacuum interrupter complies with the circuit-breaker and the disconnector standards.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: Vacuum Interrupters use a metallic cylinder to shield the ceramic from the metal vapor during arcing. Rightly so, this metallic cylinder is termed as “shield” or “arcing shield” or “vapor condensing shield”. This shield plays an equally important role in the high voltage performance of the vacuum interrupter. The number, position, dimensions and profiles of these shields govern the electrostatic field distribution and hence the high voltage performance of the vacuum interrupter. The high voltage performance of the vacuum interrupter is evaluated through analytical means like FEM simulations and high voltage tests. This paper presents the significance of the shield through results of electrostatic simulations and experimental results of commercial vacuum interrupters with various combinations of shields. The paper also presents the role of multiple shields, especially for higher voltage interrupters. A case study, highlighting the importance of the annular gap between contacts and shield for the impulse voltage performance of the contacts is also presented in this paper.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: Copper-Chromium (CuCr) based contact material is widely used for vacuum interrupter (VI) contacts and has found worldwide acceptance in medium-voltage VIs, especially for high-current interruption. Contact material with chromium content between 25 and 50 wt. % is almost exclusively used. Conventionally, copper and chromium are uniformly distributed throughout the body of the contact. In a few cases, contacts with grading of the material along the thickness have been used. This paper presents a new concept of functionally graded electrical contact which consists of CuCr50 in the bulk region and the remaining petal region consists of CuCr25. The aim of this grading is to improve the interruption ability with optimum erosion characteristics. The paper further reports the results of the investigations of switching behavior of VI with these functionally graded contact tips. The results indicate that the higher thermal and electrical conductivity as well as anti-welding properties at the required locations of the developed functionally graded contact material improved the interruption ability of the VI. The results of the switching tests are seconded by the results of the microstructural analysis (SEM/EDS) of the arced and un-arced contact tips.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: Silicon nanowires were suggested as a material in production of field emission spot like cathodes. Field emission properties of high purity silicon nanowires produced by method of melt's electrolysis of the mixture KCl-KF-K2SiF6-SiO2 were investigated. The diameters dispersion of nanowires under consideration were approximately from 10 nm to 100 nm. Nanowires originally produced as “wisp” on carbon substrate firstly were separated from substrate then were reduced to fragments and further were strengthened to tungsten cathode in a shape of spike with curvature radius approximately 0.1-1 mcm by organic binder which was evaporated in a vacuum immediately before measurements. The volt- ampere characteristics the cathodes patterns were measured for voltages from 0,5 kV to 1,5 kV. The maximum achieved stable work current was 5 μA for a voltage 3.95 kV. The threshold current leading to dramatic destruction of the wires was estimated by 10 μA. As soon as this threshold had been reached spark discharge occurred and thin film of Si on tungsten tip formed in some experiments. In this case field emission became stable up to 25 μA and started with emission voltages of 300 V. The energy distributions of emitted electrons was obtained for silicon nanowires and nanoparticles of Si on tungsten tip.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: The review on low-energy, high-current electron beams production and their application for materials surface treatment is presented. It is shown that the guns with plasma anode and explosive-emission cathode are most perspective for the generation of such beams. Problems of explosive emission excitation, as well as formation and transportation of high-current electron beams in plasma-filled diodes have been considered.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: It is important to understand dielectric strength of vacuum interrupters after no-load operation and current switching, which reflects a dielectric condition of the vacuum interrupters operating in field. Especially there is no such data available for high voltage vacuum interrupters with contact gaps reaching 30mm. The objective of this paper is to experimentally investigate the influence of three kinds of switching operations on the standard lightning impulse voltage breakdown characteristics of high voltage vacuum interrupters with a contact gap 30mm. The three kinds of switching operations are “closing without current / breaking without current”, “closing without current / breaking with 5kA current” and “closing without current / breaking dc current”. Therefore we designed six high-voltage vacuum interrupters with butt type contacts. The experimental results revealed that the conditioning process became slowly and the breakdown voltage followed the Weibull distribution after the three kinds of operations. And the operation “closing without current / breaking 5kA current” will increase the 50% breakdown voltage U50 of the vacuum interrupter from 340kV to 394kV. The U50 of the vacuum interrupter after the operation “closing without current / breaking without current” will increase from 340kV to 362kV. The operation “closing without current / breaking dc current” will increase the dielectric strength. As the current is increasing. The U50 increased from 385kV to 395kV with the breaking current 450A dc 500ms. And the U50 increased from 385kV to 437kV with the breaking current 750A dc 500ms.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: Arc sources using liquid cathode material could enable very high rate deposition of metal and metal compounds of cathode materials of low melting point. Of special interest are cathodes of zinc, cadmium, tin, and indium as they can be used to deposit high quality transparent conducting oxide films. Phase transitions are briefly reviewed using phase diagrams and vapor pressure curves, and preliminary experiments are reported using a crucible designed to hold the solid or liquid cathode material. Liquid zinc showed evidence of boiling, and liquid tin emitted less and smaller macroparticles than the same source using solid tin.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: The vacuum circuit breaker is used as the single-break, and investigation is not conducted so much about the multi-break vacuum circuit breaker at present. So, we are investigating multi-break interrupters performance and the relation between the post arc current and the voltage distribution ratio in the double-break vacuum circuit breaker. In first investigation, performances of single, double and triple-break vacuum interrupter are measured to reveal their characteristics. In the results, multi-break vacuum interrupter has better breakdown characteristics than single-break vacuum interrupter. In second investigation, the post arc current and the voltage distribution ratio were measured in order to clarify the relation between the post arc current and voltage distribution ratio. Experiments are measurement of the post arc current which flows into one vacuum interrupter, and measurement of the voltage distribution ratio and post arc current of a double-break vacuum circuit breaker. The results of investigation showed that the bias of voltage distribution ratio occurs when the post arc current value which flows into each vacuum interrupter in a double-break vacuum circuit breaker became imbalanced. In addition, it turned out that the post arc current of spiral electrode is very scattering as compared with axial magnetic field electrode. It turned out that it is better to use the axial magnetic field electrode for a double-break vacuum circuit breaker.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: The influence of lagged axial magnetic field (AMF) due to eddy current induced in contacts system on the distribution of cathode spots (CSs) in current-zero stage of vacuum arc with different current falling rates was investigated experimentally. Experiments were conducted with cup-shaped AMF contacts in a demountable vacuum chamber. The characteristic of CSs distribution of triggered vacuum arc in current-zero stage with arc current frequency of 50Hz was investigated at first with the aid of a high-speed digital camera with an exposure time of 2 microseconds. Then the characteristic of CSs distribution with faster current falling rate, which was realized by injecting a countercurrent with frequency of 500Hz or 1kHz, was investigated. Moreover, the lagged AMF flux density in current-zero stage with different current falling rates was calculated by ANSYS. Research results showed that CSs located in the center of contact plate tended to extinguish earlier than those at periphery of contact plate in fast current-zero stage due to the stronger lagged AMF in contact center.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: Voltage distribution relation of vacuum switch (VS) with multi-break determined its breaking capacity in certain degree. The distribution properties of transient recovery voltage (TRV) and dielectric recovery characteristics of vacuum switch are studied by experiment in this paper. The experimental prototype is set up. The voltage distribution of the interrupters with grading capacitors and without grading capacitors is compared. When three interrupters parallel connect different grading capacitors, short-circuit current is interrupted under the conditions of three interrupters contacts synchronous or asynchronous parting. The experimental results show that successful interruption mostly due to the good voltage sharing in the dielectric recovery process. The voltage distribution is mainly decided by interrupters' arc resistances in the dielectric recovery process, whereas it is decided by their equivalent capacitance after the dielectric recovery process. Therefore, high controllability actuator and proper grading capacitors are important factors for multi-break vacuum switch to interrupt successfully.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: Vacuum Interrupters (VIs) are designed for a long operating life. Even after a large number of switching operations they should still provide good arc extinction and be able to withstand high voltages. Switching operations produce substantial masses of metal vapor that condense on the inner component parts of the VI. The Vis are equipped with shields to protect the ceramic surfaces from being coated by metal vapor. Since the first VI was put into service, a large number of shield designs have been developed. If the shield design consists of a floating shield with two end-shields, there are two gaps between these shields. These gaps are necessary for insulation when the VI is in the open position, but during the switching operation metal vapor can flow through these gaps and coat the ceramics. If the deposited area on the alumina ceramics reaches a critical value, the dielectric performance of the VI can become reduced. Standard VIs have been tested with a floating shield and two end shields, that did not overlap the floating shield. The VIs were assembled at the Institute's high power test facility to perform switching operations at different current intensities. After opening the VIs, the coated ceramics were examined. It became clear that, the more switching operations were performed, the darker the deposited layers became. Electron Probe Micro Analysis (EPMA) is a method for surface investigations which was used here to obtain a very detailed view of the thickness of the deposited layers. With EPMA it is possible to detect very thin layers in the range of nanometers. Several coated ceramic surfaces of VIs that had been switched with different current intensities were investigated. In order to provide a better understanding of how strongly different deposited layers can affect the dielectric performance of the VI, surface resistance measurements were carried outdone. These were performed with a high resistance meter, which is able to measure up to 1016Ω using a 1 kV voltage source.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: A particular Cathode-like luminescence (CLL) phenomenon occurring on vacuum-dielectric interface under high DC electrical field before or accompanied with flashover is reported, which is widely existed in vacuum-dielectric system. It is considered that the CLL presented in this paper is initialized by field electron emission at Cathode Triple Junction (CTJ) and finally generated by a process of radiative recombination due to the self-stabilizing secondary electron emission (SSEE) and collision on surface of insulator. The spectrum of CLL is measured and analyzed, and it shows that there are not any characteristic spectrums of C, O, N, which means that the CLL is not produced by discharge of desorption gas. In addition, simulation results also approved that the SSEE process in fact exists. Finally, its relevance to flashover is also discussed. It shows that flashover seldom occurs on the channels of CLL, which seems that the CLL has an inhibition effect on flashover. However, the exact mechanism is still unclear. This work will be researched in near future.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: The dielectric target has been made of polyethylene. High voltage short pulse (150kV, 5ns) generator RADAN was used. Ion flow was analysed with Thomson spectrometer. Hydrogen ions has energies up to 400keV, deuterium and carbon ions has energies up to 5keV. There are H, D, C+1, C+2, C+3, C+4 ions in the plasma flow. Most probable energy of ion fraction depends on its ion charge. At increase the anode-dielectric gap to 2mm in the ion flow hydrogen ions are observed only, Energies of protons grow up to distance 7mm. Hydrogen ions can be accelerated by the several separate bursts having narrow energy distribution.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: In the present work, mathematical modeling of dynamics of spherical particle after its separation from an electrode is done. On the basis of quasistatic model without solving the equations of electrodynamics it is shown that, at the high enough rate of rise of electric field strength, the particle can be returned to the electrode. This conclusion gives the grounds to pay attention to a possibility of nonelementary behavior of the particle after its separating from the electrode, and in particular to a possibility of its multiple return to the electrode during large rate of voltage rise.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: The integral action coefficient value K about the advanced breaking current weighted cumulative method (BCWC) used for the VCBs' contact system electrical endurance monitoring is studied. At first, the general selecting method of integral current coefficient K value is discussed, and the existent problem in the K value selecting, calculating process and potential improving room are analyzed. Considering the distribution, characteristics and factors which impact K value, and according to the analysis results the LM-BP neural network algorithm is adopted to research how dynamically select the K value based on the engineering application. The construct process, establishing skill, selecting method and determination criteria of the hidden layer node of researched K LM-BP neural network are significantly emphasized. In order to verify the feasibility and accuracy of the proposed LM-BP neural network the K value predict process was carried out by the researched neural network and the result indicate that the net has a good network optimization ability and forecast precision. Thus the feasibility of provided method can be achieved of this work The LM-BP neural network algorithm introduced can promise the K value selected more approximate to practical engineering, which can ensure and effectively improve the predicting accuracy.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: In order to clarify the characteristics of spark conditioning carried out in parallel at several parts of electrodes, we carried out conditioning experiment to use a multi-gap electrode system with multi-rod electrodes. As a result, we found that 50% breakdown voltage after conditioning saturation differed in the multi-gap electrode system from in a single gap electrode system. In addition, we found the different process to enhance the breakdown voltage in each electrode, by comparison to the single gap electrode system.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: The characteristics of arc quench time, overvoltage and reignition condition in forcing interrupt 270V DC system with vacuum switch was investigated in this paper. The experiment focused on the Magnitude of the interruption current in DC vacuum arc, variation rate of the current and voltage at zero passage (di/dt, dv/dt), and their influence in the reignition was analyzed. The di/dt was influenced by the parameters in forcing circuit, while the dv/dt not only influenced by the frequency modulation circuits but also the parameters in forcing circuit. The overvoltage contains two type of different frequency waveform, and depended on the precharged voltage and inductance. In the experiment, three types of reignition situation were found, and the reignition was undiscovered under 450A even with the dv/dt at 2000V/us. With the current increase from 540A to 1600A, the dv/dt at reignition decreased, and the time between peak voltage and reignition point decreased too, from 850ns to 50ns. While in the test, the reignition became very easy above 2100A. Finally the test gap and frequency-modulation of TRV was also researched. Large gap (3mm) and low TRV will be useful to prevent the arc reignition.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012