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A Study on Basic Theories of the high-voltage Large-current Vacuum Arc

Author:Wang Jimei Wang Jianhua Xiu Shixin Liu Zhiyuan Wang Zhongyi Jia Shenli Jin Li
School:Xian Jiaotong University,School of Electrical Engineering

In the paper, by applying the theory of the electromagnetic field and plasma theory and combining the technique for the analysis of the measured and computer values, the theoretic and experimental validation is conducted concerning the control mechanism of the vacuum arc. Some key techniques in the actual applications are also studied so as to provide theoretic bases for the high-voltage large-current switches. The main contents and features are as follows:
1. Research on the control mechanism of the vacuum arc. The transmission equation for the arc column plasma and arc column self-generated magnetic field is established. New viewpoints are presented that the arc column is contracted in the anode area and induces the anode spot. By use of the actual test and analytic method, a research is carried out on the phenomenon that the occurrence of the anode spot controlled by the longitudinal magnetic field enables the vacuum arc to manifest the diffusion characteristics, thus presenting the L-type characteristic between the vacuum arc voltage and longitudinal magnetic field strength. Meanwhile, the research is performed on the distribution of the longitudinal magnetic field for the stabilization of the vacuum arc, the after-arc current and after-arc re-ignition characteristics for the vacuum arc, the theory and test of the vacuum arc life and shutoff characteristics, test of the micro parameters of the vacuum arc, etc. The research results have become the principles for designing the longitudinal magnetic vacuum extinguishing chamber.
2) Research on the insulation mechanisms of the vacuum extinguishing chamber. Applying the computer simulation technique, the distribution of the static electric field in the vacuum extinguishing chamber is studied. With the help of the modeling experimental devices, a computational and analytic method is put forth with the conductivity as the macro parameter and the dynamic electric field in the on-off process in the vacuum extinguishing chamber with the charged particles on the shielding cover taken into consideration. The dynamic test method is used for determining the potential of the shielding cover of the vacuum extinguishing chamber to study the recovery process of the after-arc medium strength in the vacuum extinguishing chamber. The insulation analysis is made concerning the SF6 high-voltage vacuum switch. Some of the research results are applied to the optimization design of the 72.5kV vacuum extinguishing chamber.
3) Research on the contact material and electrode structure of the vacuum extinguishing chamber. Applying the actual test and computational analytic method, a research is conducted on the relation between the contact material and on-off characteristics in the vacuum extinguishing chamber. For the first time, the Cu-Co-Ta alloy contact material is developed, the experiment showing that compared with the CuCr50 contact material, the on-off current can be increased about 30%. Based on the research on the vacuum arc control mechanism, the longitudinal magnetic contacts with the two-pole, four-pole, single arm and iron core type structure are designed, developed, popularized and applied to the actual products. A large number of patents have been applied on the research results.
4. Research on the actuating mechanisms of the vacuum switch. The key problems are experimented and studied concerning the arcing, impact and rebound, arc energy and rebounding time, etc. before the striking under the loaded switching. Under the two conditions of the contact dynamic and static gaps, the research is conducted on the degree of the influence of the arcing time on the on-off short-circuit current, and the optimal opening interval section of the contact corresponding to the short-circuit current, thus deriving optimal switching-off kinematic characteristics for the contact, proposing a dynamic matching optimization method, establishing a mathematical model for the gap between the vacuum arc contacts and resulting in obtaining the contact speed equation for keeping the arc form. The experimental statistic analysis for the arcing time is performed, and the evaluation method of the mechanical characteristics of the vacuum switch is presented. The research results are used in the optimization design of the operating mechanism of the vacuum switch.
5. Study on the actual measurement of the vacuum switch. The first detachable vacuum switch arc extinguishing chamber is turned out used for the research on the on-off arc of relatively large current. An equivalent testing method was first developed both at home and abroad satisfying the value equivalent to the actually measured results. Compared with the actually measured electric life test, the power can be saved more than 10 times and the error is not over 10%, thus tackling the problem of huge power consumption during the electric life experiment of the vacuum breaker. An invention patent has been applied.
More than 250 papers are published. 8 papers are published in IEEE. 4 papers are collected by SCI (since 1997). 60 papers are collected by EI. 18 papers are collected by ISTP. The research results are cited 216 times by related papers, with 139 times by other papers. 7 treatises are published. 9 patents are acquired. Assistance is offered to manufacturers in producing many kinds of vacuum extinguishing chambers with outstanding performances.