Temperature effects on PD statistics and endurance of inverter-fed motor insulation under repetitive square wave voltages

To study the influence of temperature on partial discharge (PD) statistics and endurance of inverter-fed motor insulation, experiments were carried out focusing on enameled wires tested under bipolar repetitive square wave voltages at different temperatures. The PD pattern, delay time, amplitude and life were obtaiaed according to a large amount of test results. Experimental results show that the influence of temperature on PD features depends significantly on the voltage frequency. At low frequency, higher temperature will give rise to more PD events with longer delay time and higher magnitude. At higher frequencies the behavior is significantly different, and the influence of temperature on PD features can be neglected. The endurance test results performed at 10 kHz indicate that, at ambient temperature, PD would be the dominant factor causing insulation breakdown, while at high temperature, the thermal aging plays an important role on the breakdown process and time.