Influence of PWM technique on breakdown in twisted pairs

Abstract

Premature insulation failure is frequently observed in the stator winding of electrical motors fed by inverter drives in industrial applications for obtaining adjustable speeds. The Power Electronic Converters using PWM technique produces pulsed waveforms having a very short rise and fall times due to the high switching frequency of IGBT's. The life of such motor winding insulation is tested using twisted pair samples prepared using enameled wires. The enamel coating of Modified Polyester (non-corona resistant material) of 40 microns thickness is used for this work. The breakdown tests were performed by applying a high frequency high voltage stress of PWM and PWM-peak waveforms with different frequency levels up to 30 kHz. The test results show that the insulation fails much earlier for PWM-peak waveform than the PWM waveform.