Influence of Voltage Overshoot in Enamel Wire Winding Insulation Systems

The voltage level used in electrical vehicles increase continuously which can be used to improve system efficiency. As the rise time decrease, the probability for overshoots in the voltage waveform however increases. The presence of overshoots increases the stress on the insulation system, particularly when partial discharge (PD) activity is introduced in the insulation. This work focus on elaborating the influence of voltage overshoot magnitude on enamel motor wire insulation with different insulation conductivity, utilizing different rise times and DC magnitudes. An approach and evaluation method to explore the performance of the insulation system is presented and demonstrated in this work. The measurement results show that the two specimens differed in the summed magnitude of PDs measured at the different flanks for all voltage levels, which is an indicator that the presence of overshoot can influence the stress level differently. Also, lower voltage levels utilizing shorter rise times can result in higher PD exposure than significantly larger ones with longer. The paper thus recommends that waveshapes which as much as possible resembles the stress in the actual application is used during insulation and product evaluations and consider the possibility for overshoots.