Investigation of Pre-Breakdown Current Based on Difference of Elapsed Time from Current Zero in VCB

In order to investigate a breakdown phenomenon occurring after current interruption, we measured currents on the order of milliamperes to amperes after current interruption. The pre-breakdown current changed depending on the elapsed time from current zero. The post arc current (PAC) rose again around the peak of the transient recovery voltage (TRV), when the breakdown occurred at the peak of the TRV. On the other hand, precursor pulsed currents were observed before breakdown from time to time, which occurred several milliseconds after current zero. The pulsed currents were on the order of milliamperes, and their time widths were on the order of 0.1 μs. The current waveform after current interruption varied according to the elapsed time from current zero. This shows that the factors involved in breakdown varied according to the elapsed time from current zero.