Research on 40.5 kV two-break vacuum circuit breaker for switching capacitor banks

Restrike during interrupting capacitor banks with vacuum circuit breakers may lead to severe switching overvoltage. Reducing the probability of restrike during capacitive current breaking is the ultimate solution to suppress overvoltage. In this paper, a new design of vacuum circuit breaker with a very low probability of restrike was proposed based on the analysis of restrike mechanism. A two-break vacuum circuit breaker was presented to carry out the duty of capacitor bank switching, and further meet the requirement of power system. A capacitive current switching test circuit has been designed, which consists of a high frequency inrush current circuit and a power frequency circuit, to perform back-to-back capacitor banks switching test. The test result shows that two-break vacuum circuit breakers can reduce the probability of restrike significantly. Short-circuit making and breaking capacity of the vacuum circuit breaker was validated by synthetic test. The optimum value of the shunt grading capacitor is 400 pF to ensure the stress of each break is approximately equal. So the design scheme of 40.5 kV two-break vacuum circuit breaker for switching capacitor banks is completely feasible.