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: The anode activities are critical for high-current vacuum arc characteristics, especially the interruption performance of vacuum interrupters. In order to understand the anode thermal process, a 2-D transient model was established. The simulation could provide temporal and spatial variation of anode temperature, the melting width and depth which have been validated by comparison with experiments. The basic features of anode erosion have been experimental investigated and the relation with the arc modes has been analyzed. A clockwise swirl flow of the liquid metal was found on anode surface under high current. Subsequent experiments indicated that the axial magnetic field (AMF) has great influence on the anode swirl flow. Both the theoretical analysis and experimental results shown that it is not the electromagnetic force but the interaction between ions from the inclined cathode plasma jets and the anode melting pool that leads to the observed swirl flow.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: The angular distribution of the metal and gaseous ion flow from vacuum arc plasma has been investigated. A Mevva-type ion source and a Time-of-Flight (TOF) mass-spectrometer were used. The experiments were performed using a range of different cathode materials, including C, Al, Zn, Cu, Ti, Co, Cr, W, Pb, Cu0.7Cr0.3, W0.4Co0.17C0.43, and Zn0.4Pb0.6, over a range of vacuum arc discharge parameters. Variable parameters in this study were vacuum arc discharge current, background gas pressure, configuration of cathode-anode gap, and composition of cathode material. A comparison with results obtained by other authors was made. The influence of discharge parameters on the ion angular distribution in a vacuum arc source is discussed.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: Various prototypes designs of 36 kV vacuum interrupters have been tested in high-power test station during capacitive switching operations. Back-to-back tests were performed for inrush current of 20 kA peak level and 4250 Hz frequency. Experiment was performed with a number of prototype vacuum interrupters of different geometry and contact material. Vacuum gap behavior under pre-arcing and inrush current conditions (pre-arc energy, duration and interruption of inrush current) will be highlighted. Field electron emission measurement has been used to monitor field electron emission current that flows in vacuum gaps after current interruption. Statistics will be presented in relation to the late breakdown events, field electron emission current measurement, vacuum interrupters design and contact material. It was observed that only the mechanism of electron field emission alone could not explain the breakdown in vacuum at the origin of late breakdown phenomena. Contact material, vacuum interrupter design as well as circuit breaker characteristics are determining the dielectric withstand during capacitor bank switching operations.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: Field electron emission (FEE) current in the open(ing) gap of nine different designs of 36 kV vacuum interrupters under standard recovery voltage conditions was measured during full-power back-to-back capacitive switching. During closing operation, 20 kA inrush current (@ 4250 Hz) was applied. The measurement system is described, able to measure FEE current with a threshold of 30 μA but that also has to withstand a full capacitor bank discharge current of up to 40 kA after re-strike. It was concluded that in spite of the wide variety of measured FEE current magnitude (up to several mA) there is no direct relationship between magnitude of FEE current and probability of breakdown. Longer arc duration of the normal load current reduces the FEE current level after load current interruption.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: The paper deals with the creation of vacuum ionplasma coatings based on Ti-C-Si with additionally by ion bombardment. Shows the results of studies of the electrode potential, corrosion and relaxation resistance of samples coated with submicrocrystalline structure based on the TiC-Si, were tested for thermal cycling. The obtained results of the study makes it possible to evaluate the benefits of coatings with SMC structure to multilayer and monolayer coatings.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: A newly developed coil-type electrode structure for high voltage vacuum interrupter (VI) of 170kV voltage level is presented in this paper. To evaluate the design results of electrode structure, magnetic field distributions on the center plane of gap between electrodes and on the surface of contact electrodes are measured, and the vacuum arc behaviors during the current interruption in the vacuum chamber are observed. The multi-shield structure is suggested as the internal floating shield. The experimental results of the sample electrode and internal shield structure are compared with FE analysis results. The current interrupting tests are performed to evaluate the current breaking performance of 170kV VI according to IEC 62271-100.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: Starting from a transient equivalent model of a triple-break 126 kV vacuum circuit breaker (VCB) containing a dielectric reignition criterion, the reignition current waveform of the vacuum interrupter (VI) which took over the higher part of the transient recovery voltage (TRV) was simulated. A series damped resistor was added in the grading capacitor branch to extinguish the reignition current as early as possible. The results show that the effect of the damped resistor is optimal when its value is threshold between oscillatory and non-oscillatory decay. Excessive TRV which appeared across other un-reignition VIs and power frequency recovery voltage (PFRV) which appeared across the reignition VI were simulated. A metal oxide arrester (MOA) was installed in parallel with each VI to ensure breaking successfully by limiting the excessive TRV and PFRV. It is shown that the voltage limiting effect is preferable when a MOA with the reference voltage of 50 kV is in parallel with a grading capacitor of 1000 pF, also the thermal limit can be satisfied. Research results are expected to provide a basis for choosing proper dynamic voltage sharing measures for a triple-break 126 kV VCB.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: A new two-contact system with double-TMF structure is investigated regarding its potential for high current interruption. It consists in two co-axial TMF contacts in which the inner contact has a disk-shape structure (spiral contacts) and an outer contact with cup-shape structure. This contacts assembly gives some advantages over the single-TMF contacts one, as the high current constricted arc might split between both, inner and outer contacts or commute to the outer contact and continues its rotation. For both scenarios we normally get a larger distribution of the arc energy over the contacts surface. B-field simulation and Lorentz forces evaluation were carried out to understand the interaction between two assumed co-existing arc columns. Single phase current interruption tests were carried out to compare the performance of double-TMF contacts system with the single-TMF one. The double-TMF vacuum interrupter has revealed superior current interruption performance, 25% higher than the single-TMF one.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: In this paper, the morphological changes and arc-voltage characteristics of vacuum arc at intermediate frequency (400Hz~800Hz) were investigated under transverse magnetic field (TMF). The experiment was performed on cup-type TMF contacts with a contact diameter of 40mm and a contact gap of 2mm in single-frequency circuit. With high-speed photography, we characterized the appearance of the arc at different current of intermediate frequency. When current value increases from 3kA to 10kA the arc morphology changes obviously. When current value is 3kA (current frequency 400Hz-800Hz), there is almost no split arc, while more than 6kA (current frequency 400Hz-800Hz), the arc rotates at high speed and also split arc can be observed. The split arc can be observed at different frequency and the arc-voltage with no noise component when it occurred. Furthermore, the arc voltage at the peak current increases almost linearly with the total current at the same frequency. As the current frequency increases, the arc voltage at the peak current also increases at the same current.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: Features of structure formation of the coatings on basis of M2 steel obtained by multiple-pass E-beam vacuum deposition were investigated. It was established that multimodal size distribution (d1=3.8 μm, d2=0.65 μm, d3
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: The contacts closing impact phenomenon of vacuum interrupter is a basic event in a vacuum circuit breaker, which reveals lots of information including impact force, bouncing duration, stress distribution and so on. The objective of this paper is to investigate the contacts impact phenomenon in a 126 kV vacuum circuit breakers. PVDF (polyvinyldene fluoride) piezoelectric sensors were used to measure impact force of a 126 kV vacuum circuit breaker at a closing velocity of 1.5 m/s. In addition, a finite element analysis simulation model of contacts impact in a 126 kV vacuum interrupters was set up by using ANSYS / LS-DYNA software. The experimental results showed that the maximum contacts impact force of a 126 kV vacuum circuit breaker was about 105 N at 1.5 m/s closing velocity, which is are in good agreement with the simulation results. And the simulation results also showed that the maximum impact force, durations of contact bounce and the maximum stresses of contact were related with some parameters of vacuum interrupter, such as contact shape, elastic modulus of contact material, impact velocity and contact spring force.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: Cathode spots (CSs) expansion speed in the initial expansion stage in high-current triggered vacuum arc was investigated experimentally. Experiments were conducted with butt contacts in a demountable vacuum chamber. Alternating current with frequency of 50Hz and peak value of 3kA~11kA was used. Images of CSs were photographed with a high-speed digital camera with exposure time of 2 microseconds. The influence of arc current rise rate and axial magnetic field (AMF), which was supplied by external magnetic field coil, on CSs expansion speed was mainly investigated. Experimental results indicated that, in the initial expansion stage, as the arc current increased linearly, CSs expansion speed was nearly a constant, which was proportional to the current rise rate. Experimental results also showed that CSs expansion speed decreased with the increase of AMF flux density.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: In this report we present state of work under development of LTD stages with air insulation in a primary circuit and vacuum insulation in a secondary turn. Special unit, named capacitor block, was developed for use as a main structural element of the transformer stages. It incorporates two capacitors GA 35426 (40 nF, 100 kV) and multichannel multigap gas switch. Two types of stages were developed: 1) Stage LTD-20 with 4 modules in parallel and 5 capacitor blocks in each module. In tests of this stage current amplitude up to 850 kA with ~ 140 ns rise time was obtained on a 0.05 Ω load at 100 kV charging voltage. 2) Stage LTD-4 with 2 modules in parallel and 2 capacitor blocks in each module. Several installations were built on base of these stages, including linear transformer, consisting of two identical LTD-20 stages in series, and high power electron accelerator on base of LTD-4 stages. Design of installations and tests results are presented and discussed in this report.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: This paper deals with the charge depression effect of a shield ring, a ring type electrode, which is applied to high voltage vacuum devices in order to relax the electric field near the triple junction on a cathode. In the present study the shield ring is located in an insulating hollow cylinder made of Al2O3, and the charge distribution on the inner surface is measured by employing an electrostatic method. As a result, we have obtained the charge distribution patterns for several ring heights. The results are discussed together with calculated charge distributions.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: The paper focuses on the stages of dense and superdense glow discharges. The process of discharge development is considered. The data on threshold current density at the cathode, at which the discharge passes from the dense phase of a glow discharge to a superdense glow form, are presented for various gases. The causes that initiate this transition are analyzed. Analysis of birth-death processes of charged particles in plasma based on measuring the discharge parameters is carried out. The mechanisms of charge transport and energy input into plasma are considered.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012
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    ABSTRACT: Alumina ceramics is widely used as an insulating material for high voltage devices, because of low outgassing, hardness, low dielectric loss and high bulk breakdown voltage. However, there is serious problem to solve that the flashover voltage along the surface in vacuum is lower than that of a vacuum gap at the same length between electrodes. Many intensive researches have been carried out to improve surface flashover voltage in vacuum. Even so the mechanism of surface flashover is not always clarified yet. One of reason is expected to charging characteristics which depend on the material properties of insulator. In this paper, we focused on the relationship between vacuum flashover characteristics and surface charge caused by high voltage application and surface flashover occurrence for three kinds of alumina ceramics.
    Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012