Partial discharge and aging phenomena in insulation systems of rotating machines fed by power electronics

This paper deals with partial discharge measurements carried out on specimens of Type I and Type II insulation systems for rotating machines. Partial discharge (PD) patterns under sinusoidal and repetitive impulse voltage, considering two level and five level inverters, are presented showing that phenomenology is deeply different, but that increasing the number of inverter steps, PD patterns closer to those obtained under sinusoidal supply voltages can be obtained. The different characteristics, magnitude and repetition rate of PD varying the voltage supply waveshape have significant impact on life and insulation system reliability, for both Type I and Type II insulation.