The partial discharge（PD） test system is set up 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

we performed PD tests on single discharge models made up of enameled wires used in low-voltage inverter-fed motor insulation under sinusoidal and repetitive square wave voltage with 200 ns rise times. Moreover

we analyzed single PD pulse magnitude

phase distribution in time domain

energy distribution in frequency domain

and the statistical PD patterns. Conclusions can be drawn 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 are around 10 times and 1/3 times of those at sinusoidal voltages. Therefore

when performing insulation evaluation on inverter-fed motors according to standards released by International Electrotechnical Commission

PD and endurance test system should be considered carefully on the basis of the influence of repetitive square wave voltage parameters on PD and endurance characteristics.