Effect of extended grading capacitor on the interrupting performance of multi-break circuit breaker during out-of-step faults

Abstract

The extended grading capacitor (EGC) installed in parallel to multi-break circuit breaker (CB) chamber is a promising technique to suppress secondary arc. The effect of EGC on the interrupting performance of CB during is investigated in this paper. As CBs are subject to various operating burdens in practice, this paper is mainly devoted to the out-of-step fault. Considering the most severe condition, an equivalent circuit model for UHV line is established; the voltages on power source side and line side are derived based on Laplace transform and travelling wave theory, respectively; the expressions of transient recovery voltage (TRV) across CB contact are obtained, and hence the rate of rise of recovery voltage (RRRV). Since the CBs of two power source sides are often cleared asynchronous with a very small-time deviation, the characteristics of TRV waveform for them are separately computed and analysed. Furthermore, a series of sensitivity analysis have been performed. The influences of phase angle, parallel line, shunt reactor as well as reclosure on the interrupting performance are discussed. The results suggest that performance of CB during out-of-step fault is jointly determined by phase angle, parallel line, and especially the reclosure strategy. The EGC can smooth the TRV significantly especially during the first few microseconds of out-of-step fault, the breaking capability would be enhanced.