Deterioration of Stator Winding Insulation in Inverter-Fed Traction Motors

Understanding of deterioration of the stator winding insulation in inverter-fed traction motors is significant for its diagnosis, maintenance, reliability or health assessment. In this paper, the diagnostic parameters of the stator winding insulation of the traction inverter-fed motors with various years of service, including insulation resistance, dissipation factor, partial discharge inception voltage (PDIV) and residual breakdown voltage, were measured. The insulation material from the various spots of the ground-wall insulation along the coil were sampled and analyzed with thermogravimetric analysis (TGA). The measured results show that the diagnostic parameters from the stator windings changed in comparison with ones of the new motor. The insulation resistance, dissipation factor, PDIV and residual breakdown voltage values at the top half-coils are higher than those at the bottom half-coils with the serviced motors. In general there was the more insulation deterioration in the bottom half-coils than in the top half-coils. The TGA results from the sampled insulation material indicate that the stator winding insulation in the inverter-fed traction motors with a service period up to ten years shows slight aging. The most insulation breakdown spots occurred at the first or second turn of a coil near the slot exit of the motor stators.