PD characteristics and mechanisms in artificial air-filled voids at room and liquid nitrogen temperatures

In this study, partial discharge (PD) characteristics in artificial air-filled voids at room and liquid nitrogen temperatures were investigated experimentally. It was found that minimum PD inception voltage at liquid nitrogen temperature (77 K) decreased with decrease in ambient temperature due to condensation of oxygen in the void. By observation of PD current pulses and light images, it was found that there were three modes of discharge: streamer, Townsend and glow like discharges in PD at room and liquid nitrogen temperatures. Especially the mode at liquid nitrogen temperature changes markedly with the stress time.