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

Restrike caused by interrupting capacitor banks with vacuum circuit breakers will lead to severe switching overvoltage, which may cause great damage to power system. Reducing the probability of restrike during capacitive current breaking is the ultimate solution to limit overvoltage. In this paper, a new design of vacuum circuit breaker with a very low probability of restrike is proposed based on the analysis of restrike mechanism. A kind of vacuum circuit breaker with two breaks is presented, to carry out the duty of capacitor bank switching, and further meet the requirement of class C2 in IEC terms. A capacitive current switching test circuit is developed, which consisted of a high frequency inrush current circuit and a power frequency circuit, to perform back-to-back capacitor banks switching test. The test results show that two-break vacuum circuit breakers can reduce the probability of restrike significantly; short-circuit making and breaking capacity of the vacuum circuit breakers is validated by synthetic test. The optimum value of the shunt grading capacitor is determined to ensure the stress of each break is approximately equal.