Experimental comparison of partial discharge between fast-switching pulse waves and square waves

Abstract

The behaviour of partial discharge has been examined for unipolar turn-to-turn-like waveforms with short 10%-90% rise-times of approximately 25 ns. Such waveforms simulate what may be seen between turns on random-wound inverter-fed electrical machines driven by ultra-fast switching wide-bandgap power semiconductors. The influence of pressure, voltage polarity, and pulse duration was examined, with particular focus on environments relevant to aerospace. Pulse waves were observed to generate distinct partial discharge behaviour relative to square waves, with important implications for detection and lifetime assessment. Partial discharge likelihood for pulse waves at a given voltage was reduced, with comparable discharge activity requiring an additional several hundred volts at both ambient pressure and 116 hPa. Partial discharge events typically occur sooner after voltage rise for shorter duration pulses, whereas discharges occasionally occurred over 1 ms after voltage rise for longer-duration 10-100 Hz square waves at lower pressures, which may be outside the window of detection of some instrumentation. While observations and stochastic behaviour were interpreted within the context of space charge and the latest understanding of Volume-Time theory, some observations have not been able to be accounted for. These include observed stochastic trends between partial discharge delay time and unipolar pulse duration not correlating well, a reduced delay between voltage change and partial discharge activity during voltage fall relative to rise, and the lack of observed partial discharge activity after voltage fall for unipolar voltage pulse durations less than 50 μs.