Influence of switching frequency of the voltage waveforms on breakdown in twisted pairs

Insulation degradation in the stator winding of electrical motors fed by inverter drives has been concerned about researchers over the last two decades for obtaining adjustable speeds. The Power Electronic Converters produces a PWM waveform with fast rising pulses due to high switching frequency of IGBT's, cause's premature failure of motor winding insulation. To simulate the breakdown of motor insulation, twisted pair samples prepared using enamel wires are tested. The enamel coating is of Modified polyester (Class-F insulation) with different makes have the same thickness of 40 microns are used for testing in this work and the results are compared. The tests were performed by applying high voltage, high frequency stress of sine, triangular and square waveforms with different frequency levels of 10 KHz, 20 KHz, and 30 KHz. The test results show that the breakdown strength of the various makes with the same thickness of same enamel material differs. Moreover, as the switching frequency is increased, the life of the motor insulation is reduced.