Partial discharge characteristics of inverter-fed motor insulation at repetitive square wave voltages

In order to increase the signal-to-noise ratio of partial discharge (PD) detection on inverter-fed motors, both time and frequency features of PD and generator induced disturbance were studied under square-wave voltages with 200 ns rising time, and PD statistical characteristics with different square-wave voltage frequencies and duty cycles were obtained. Experimental results show that, the frequency energy of PD and generator induced disturbance mainly distribute in frequency ranges of 0~1.8 GHz and 0~0.5 GHz, respectively. Higher square-wave voltage frequency will give rise to PD pulses with lower magnitude, and square-wave voltage having small duty cycle will have PD submerged in the generator disturbance during voltage fall. Accordingly, when performing PD detections on inverter-fed motors, to suppress the power disturbance, high pass filters with cut frequency of 0.5 GHz should be adopted, and ultra high frequency sensors should have excellent response performance in the frequency range of 0.5~1.8 GHz. Furthermore, to increase the signal-to-noise ratio, repetitive square-wave voltages having frequency less than 200 Hz and duty cycle of 50% is recommended to be the testing voltages.