The influence of repetitive square wave voltage rise time on partial discharge inception voltage

Repetitive wave voltages should be used to perform partial discharge inception voltage (PDIV) tests on insulation systems of type I rotating machines fed by power electronics in qualification and type tests according to new standards published by International Electrotechnical Commission (IEC). To obtain objective test results, the influence of waveform parameters on PDIV results should be carefully considered and thus accordingly, the appropriate waveform selected. From previous research, we concluded that the rise time of repetitive square wave voltages can influence PD statistics in both time/frequency domain and the endurance of enameled wires. This study aims to investigate the influence of rise time on PDIV in inverter-fed motor insulation on the basis of PDIV tests performed on twisted pairs made out of enameled wires under bipolar and unipolar voltages of different rise times. Experimental results indicate that the influence of impulsive voltage rise time on inception voltage depends significantly on the overshoot voltage shape and duration time at the voltage rising and falling flanks. Repetitive square wave voltage with very short rise time and high overshoot voltage tends to give rise to higher PDIV results. Moreover, we found that the influence of voltage polarity on PDIV is significant. Relatively higher PDIV will be obtained at bipolar voltages than that at unipolar voltages (positive and negative), which could be attributed to the space charge distribution and accumulation inner insulation before PD activities.