Accelerated aging, partial discharges and breakdown of Type II turn-to-turn insulation system of rotating machines

Type II insulation systems, typical of MV motors or generators, were aged under sequential thermal cycling and voltage, and diagnostic quantities related to partial discharge activity recorded, such as partial discharge inception voltage (PDIV). Accelerated aging was carried out until breakdown statistics was reached. Sinusoidal and impulsive voltage waveforms were used, with the purpose of comparing breakdown times and PD phenomenology changing supply voltage waveform and rise time. The results undoubtedly indicate that the shape of the waveform, particularly the rise time, can affect dramatically both PD phenomenology and life.