Impulse partial discharge and breakdown mechanism under non-uniform electric field in N2/SF6 gas mixtures

Partial discharge inception voltage (PDIV₅₀) with 50% probability and breakdown voltage (BDV₅₀) were measured in N₂/SF₆ gas mixtures under non-uniform electric field for positive lightning impulse voltage application. In order to investigate partial discharge (PD) and breakdown (BD) mechanisms, PD step length and time interval of PD pulses were discussed through the simultaneous measurement of current, light intensity waveforms, streak and still light emission images of the impulse PD. Experimental results revealed the stepwise propagation of the impulse PD and the relationship between the time interval of consecutive PD pulses and the step propagation length.