Safe stroke of vacuum breaking process in DC circuit breaker commutated by intermediate frequency current

Abstract

The safe stroke between contacts of vacuum switch is the key parameter that can withstand transient recovery voltage (TRV) after arc extinction. In order to determine the minimum safe stroke during direct current (DC) interruption, this paper starts with the characteristic analysis of the commutation process. After breaking current zero crossing, contact gap is used to correlate the dielectric recovery level with TRV. In terms of theoretical description, based on the sheath development analysis of continuous transition model (CTM), different commutation moments and frequency have a perceptible effect on the TRV and dielectric recovery process. The breaking test of DC synthesis circuit with dual power supply is used to further verify the dielectric recovery level of vacuum gap, and the minimum safe stroke corresponding to reliable interruption. Simulation and experimental results show that safe stroke increases with the higher breaking current, TRV and its change rate during the DC breaking process, the corresponding commutation moment should be delayed. Finally, the influence of arc appearance on the safe stroke is discussed by analyzing the arc image of the draw-arc process. The safe stroke is helpful to determine the time setting for commutation moment and reliable breaking process of DC vacuum circuit breaker.