Time behavior of partial discharges and life of type II turn insulation specimens under repetitive impulse and sinusoidal waveforms

Rotating machines controlled by power electronics are becoming more-and-more common in medium voltage assets, including renewable generation and industrial plants. The design of rotating machine bar insulation under AC sinusoidal waveform is well understood, but the peculiarities of the overvoltage, electric field distribution, and partial discharge (PD) experienced by the insulation when fed by a pulse width modulator (PWM) require new testing procedures, and the International Electrotechnical Commission (IEC) is now involved in the standardization [1]- [10]. The purpose is to provide adjustable speed drives and, in general, rotating machines controlled by power electronics, having the same level of reliability as conventional, power supplied, machines, which may not be the case at the present time. This article shows the influence on aging of turn-to-turn insulation samples from repetitive impulses compared to AC sinusoidal voltage, highlighting the partial discharge phenomenology changes and, depending on the energy and the risetime of the impulses, their influence on lifetimes.