Analysis of steep-fronted voltage distribution and turn insulation failure in inverter fed AC motor

As a potential source of turn insulation failure, the steep-fronted voltage at the AC motor terminal generated by PWM drive switching or cable ringing is not uniformly distributed among the coils of the windings and among the turns of the coils. This paper presents a detailed electromagnetic analysis of the parameters of a transient model of coil and coil group which includes iron loss, skin and proximity effects. A finite difference method is applied to solve the model for the inter-turn and inter-coil voltage distributions. The detailed time-domain modeling is compared to a frequency-domain modeling solved by the lattice diagram method and to test results. A turn insulation surge-withstanding capability study is then presented with a flexible insulation test system