Experimental investigations on the post-arc current of the vacuum circuit breaker in an active mechanical DC circuit breaker

Abstract

Vacuum circuit breakers (VCB) are commonly used in active mechanical direct current circuit breakers (DC CBs) to accomplish the interruption of the fault current. The post-arc current phenomenon of a VCB is related to the dielectric recovery process of the VCB. Thus, we performed experiments to investigate the influence on the post-arc current by taking the electrode separation, breaking current, and interruption of the bi-directional current with the injecting high frequency current in a fixed direction into account. To be in accordance with the practical interruption duty, the breaking current in the experiment ranges from 500 A to 20 kA. At the same time, the di/dt at current zero (CZ) varies between 200 and 1100 A/μs. The experiment results reveal that the peak value of the post-arc current in an active DC circuit breaker can reach more than 100 A with high di/dt at CZ. It is found that with a longer electrode separation, not only the residual charge increases but also the post-arc current increases. The arcing current before CZ can influence the post-arc current but the effective duration before CZ is short. This duration is the memory time and it is derived from the experiment results. The influence of the breaking current and interruption of the bi-directional current with the injecting current in a fixed direction are dependent on the relation of the current commutation time with the memory time.