Dynamic dielectric recovery and statistical charac

2022-07-26
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Dynamic dielectric recovery and statistical characteristic analysis of multi break vacuum switch

1 introduction

vacuum switch is a new type of switching device in power system. It is characterized by using vacuum as the insulation medium and arc extinguishing medium between main contacts. The extremely excellent insulation strength and arc extinguishing ability of vacuum bring many advantages to vacuum switch, which has been widely developed and applied in the field of power distribution. On the other hand, due to the insurmountable difficulties in the insulation of long true space gap, the current vacuum switch can only be applied to the voltage level of 110kV and below. There are two ways to develop vacuum switches with higher voltage levels: one is to continue to develop single break vacuum switches, such as 123kv, 31.5KA vacuum circuit breakers developed by Japan mingdianshe company in 1980; 145kV, 31.5KA vacuum circuit breaker developed by Toshiba in 1987; Second, develop double break and multi break true novodur HD m203fc G3 air switches certified in relevant provisions of ISO 10993, such as 168kv, 40ka double break vacuum circuit breaker developed by American General Electric Company in 1980; 145kV double break vacuum circuit breaker developed by Westinghouse Electric Company; In 1985, the former Soviet Union produced 110KV, 25kA multi break vacuum circuit breakers in series with four arc extinguishing chambers; Mitsubishi Corporation of Japan plans to develop 500kV Double break vacuum circuit breaker [1, 2]

the source of great interest in multi break vacuum switch technology is based on technical and economic considerations. Because multi break vacuum switch has many advantages, multi break vacuum circuit breaker has become a research topic in many countries [3~7]. At the same time, the development of multi break vacuum circuit breaker also involves many research topics. The most important one is the theoretical study of its basic breaking mechanism, but there is no more in-depth report on this research at home and abroad. The slow progress of theoretical research restricts the technology from going through the friction coefficient function of measurement data to industrial application. This paper attempts to theoretically deduce the maximum possible growth multiple of multi break vacuum switch from the study of dynamic dielectric recovery process after arc of double break vacuum switch, and uses the concept of "breakdown weakness" [8~10] and introduces the random theory and probability statistical method in the field of mathematics to analyze the mechanism of breaking, dielectric recovery and re striking of double break and multi break vacuum switch, The conclusions obtained are beneficial to the further study of multi break vacuum switch

2 dynamic dielectric recovery process of double break vacuum switch

for single break vacuum switch, the post arc dielectric recovery process of vacuum arc extinguishing chamber refers to the process that the gap of vacuum arc extinguishing chamber gradually recovers from the high conductivity state during arcing to the high resistance insulation state after the current crosses zero and the arc is extinguished. The strength recovery characteristic of the post arc dielectric of the vacuum interrupter directly determines the breaking capacity of the vacuum interrupter if it needs high wear resistance. Therefore, it has been concerned by the majority of researchers and a lot of research has been done in this field. The post arc dielectric strength recovery of vacuum interrupter includes two aspects: inherent dielectric strength recovery and dynamic (actual) dielectric strength recovery [11]. The inherent dielectric strength recovery characteristic refers to the recovery characteristic of the arc extinguishing chamber under the action of no transient recovery voltage. It is an ideal recovery characteristic and the basis for studying the actual dielectric recovery characteristics. Under actual operating conditions, both ends of the vacuum circuit breaker will be affected by the rapidly rising transient recovery voltage (TRV) immediately after breaking the current. The dielectric recovery under this condition is called dynamic (actual) dielectric recovery. For a double break vacuum switch, the dynamic dielectric recovery process is quite different from that of a single break vacuum switch

2.1 equivalent model of double break vacuum switch

the biggest advantage of double break vacuum switch technology is to obtain the current breaking capacity of high voltage level after the arc extinguishing chambers of low voltage level are connected in series. Figure 1 shows the synthetic test circuit of the double break vacuum switch. The effective value of current source is 25kA, and the peak recovery voltage of voltage source is 100kV. Here, the double break arc extinguishing chamber is arranged from top to bottom. For the double break vacuum switch shown in Figure 1, when the recovery voltage of the synthetic circuit is added, the change rate of the recovery voltage applied at both ends of the vacuum gap is very high (the average rise rate of the recovery voltage can reach 2~10kv/ms) [3~5], so the voltage distribution of the two vacuum interrupters is mainly affected by the capacitance of the vacuum gap (the influence of the arc gap resistance is not discussed temporarily), and the equivalent circuit diagram of the double break vacuum switch can be obtained, As shown in the solid line in Figure 2. 2.2 dynamic medium recovery process of double break vacuum switch

double so as to reduce the pollution caused by waste water and waste gas. The dynamic medium recovery process of double break vacuum switch is different from that of single break vacuum switch. During the breaking process of the double break vacuum switch, due to the uneven partial voltage of the upper and lower vacuum arc extinguishing chambers (due to the influence of the capacitance CG to the ground), the arc extinguishing chamber with higher recovery voltage is usually re struck first. At this time, as long as the peak value and rising speed of the recovery voltage are lower than a certain limit value, the whole double break switch will not fail due to the re striking of an arc extinguishing chamber. This is because the dielectric strength of the other vacuum arc extinguishing chamber may still be higher than the recovery voltage at this time, and it can also withstand the whole recovery voltage for a relatively short time. When the dielectric of the heavily penetrated vacuum arc extinguishing chamber recovers, it will jointly complete the breaking process. Fig. 3 is the oscillogram of the recovery process of a typical double break vacuum switch. It can be seen from Figure 3 that at point ①, when vi2 (vacuum arc extinguishing chamber at the upper end) is about 8ms after the current zero point and the recovery voltage is -49kv, a re striking occurs, and it can be seen that the voltage of u42 drops to zero. At this time, VI1 (vacuum arc extinguishing chamber at the lower end) bears the whole recovery voltage, and its voltage value soon increases from -18kv to -78kv. In section ②, the vi2 medium recovers quickly and can bear part of the recovery voltage. Here, it can be seen that VI1 has withstood the recovery voltage of more than -60kv for 12ms, and finally its recovery voltage

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