Detection and Analysis of Partial Discharges under PWM Voltage Excitation

Abstract

Pulse width modulation (PWM) is commonly used in variable speed drives to generate excitation voltage for industrial motors. The strong interference caused by the high frequency switching of the PWM voltage affects the measurement of partial discharges (PD) for motor insulation condition assessment. This paper proposed a time domain-based software filter to eliminate the switching interference from the measured data and extract the discharge signal for analysis. It was shown that the switching interference waveform is steady enough to provide an effective basis for the filtering algorithm. Experiments were carried out to investigate the characteristics of surface discharges under sinusoidal PWM (SPWM) excitation, and the effects of different voltage levels on the relationship between the PD magnitudes and the time lag. It was observed that the larger the discharge magnitude the shorter the time lag of discharge occurrence.