Inverter design and partial discharge phenomenology in insulation systems of rotating machines

This paper focuses on aging and breakdown of insulation systems of rotating machines (Type I insulation). Specifically, it deals with the partial discharge (PD) phenomenology, comparing the PD behavior of phase to ground and turn insulation under sinusoidal and PWM-type voltage. Two-level and multilevel inverter design, with different rise times of the repetitive voltage impulses generated by the inverter, are considered and the relevant PD patterns displayed. Indication on how to measure PD under the noisy environment brought about by power electronics supply, as well as PD patterns due to interface discharge phenomena are reported. It is shown that typology and design of the inverter and of the electronic switches can influence significantly PD behavior, insulation system life and, thus, machine insulation reliability.