Study on transient recovery voltage distribution mechanism and grading capacitor of double-break vacuum circuit breaker

To keep the uniform distribution of the transient recovery voltage (TRV) across each vacuum interrupter (VI) is very important for the breaking capability of double-break vacuum circuit breakers (VCBs). According to the transient equivalent circuit of double-break VCBs, a mathematical model describing the TRV distribution characteristics was established; it revealed that the bias of TRV distribution was caused by the stray capacitance and the imbalanced post-arc plasma characteristics in each VI. The validity of the TRV distribution model was proved by simulation results based on a vacuum arc model. The experimental results under different values of grading capacitors demonstrated their effectiveness in improving the even degree of the TRV distribution in double-break VCBs. However, too large grading capacitor significantly magnified the amplitude and duration of the reignition current, which was detrimental to the successful breaking of double-break VCBs. It is advisable for this reason to limit the value of grading capacitors to those ranges which can guarantee sufficiently improve the TRV distribution.