Influence of square waveform on life of twisted pairs due to power electronic converters

Issues in the life of stator winding of electrical motors fed by inverter drives have been concerned about researchers over the last two decades for obtaining adjustable speeds.The Power Electronic Converters produces a square waveform (duty cycle, 50%) with fast rising pulses due to the high switching frequency of IGBT’s, causes premature failure of motor winding insulation. The Life of such motor insulation is tested using twisted pair samples which are prepared using enamel wires.The enamel coating is of Modified Polyester (Class-F insulation) with different makes have the same thickness of 40 microns and Polyester-imide (Class-H insulation) thickness of 40 microns are the two primary insulation tested in this work and the results are compared. The breakdown test was performed with high voltage power frequency sinusoidal waveform and high frequency square waveform of different frequency levels of 5 kHz to 30 kHz. The test results show that breakdown strength of Class F insulation is more than that of Class H insulation.