Comparative study of PD characteristics for inverter-fed motor insulation under sinusoidal and repetitive square wave voltage conditions

Abstract

The partial discharge (PD) test system is setup based on ultra-high frequency technologies in order to study PD characteristics for inverter-fed motor insulation under both sinusoidal and repetitive square wave voltage conditions. Resorting to the system, PD tests are performed on single discharge models made out of enameled wires used in low-voltage inverter-fed motor insulation under sinusoidal and repetitive square wave voltages with 200 ns rise times. Experimental results show that repetitive square wave and sinusoidal voltages having same peak-to-peak voltage and frequency can produce PD with significantly different magnitude, phase, and energy distribution as well as endurance lifetime. The PD magnitude and insulation endurance under repetitive square wave voltages show seven times higher and three times shorter than those obtained at sinusoidal voltages. Accordingly, when performing insulation evaluation on inverter-fed motors according to standards released by International Electrotechnical Commission, it is recommended to use repetitive square wave voltages and the influence of square wave voltage parameters on PD and endurance test results should be considered carefully.