Effect of voltage waveform on partial discharge characteristics and insulation life

Polymer materials are susceptible to electro-thermal coupled stresses, which may cause changes of microstructure and degradation of physical and chemical properties, or even bring about accelerated insulation aging and premature failure. Partial discharge (PD) is considered as the main cause of premature insulation failure in high frequency equipment, such as the converter valve, inverter-fed motor and power electronic transformers (PET). And voltage waveform has significant impacts on PD. This paper focuses on the effect of voltage waveform with high frequency on partial discharge characteristics, the insulation aging process and the insulation lifetime. In order to study the influence of high frequency repetitive pulses with different waveforms on the insulation life of polymers, a PD test system was set up, which can simulate the high frequency electro-thermal coupled stresses on insulation materials. Under the constant temperature and humidity conditions, aging tests were conducted on polyimide films, which are subjected to surface discharges under different voltage waveforms, including sinusoidal wave, bipolar square wave, triangle wave and repetitive pulse with frequency of 1 kHz. During the aging test, lifetime and partial discharge characteristics, including discharge amplitude, discharge number, were recorded. In terms of these data, phase resolved partial discharge pattern (PRPD) and insulation lifetime plot relevant to voltage waveform are computed, and the correlation between lifetime and discharge characteristics is built. Experimental results reveal the aging mechanism from high frequency electrical stresses under different waveforms based on the analyses of lifetime and discharge characteristics of specimens.