Insulation failure of inter-turn insulation in inverter-fed traction motor

Partial discharge (PD) under a sequence of high-frequency pulse is one of the key factors which lead to premature failure of turn insulation of inverter-fed motors. Aging experiments for turn insulation samples under bipolar continuous square impulse voltage were done. The number and mean quantity of PDs under impulse voltage has been studied. By means of scanning electron microscope (SEM), the microcosmic morphology of surface of turn insulation was analyzed. The results reveal that the relationship of PD parameters (PD number and mean PD quantity) and aging time is complicated. The damage to polyimide nano-composite film structure is concentrated on the degradation of polymer matrix in the presence of PDs. The residual nano-fillers remained on the surface and formed a screen layer to resist the further damage of PDs. It is the symbol of faults expanding rapidly when the floccules and voids formed on the surface, which means insulation failure.