Voltage stresses on stator windings of induction motors driven by IGBT PWM inverters

In the IGBT PWM inverter, insulation breakdown and irregular voltage distribution on stator winding due to high rate of voltage rise (dv/dt) caused by high-frequency switching and impedance mismatches between inverter and motor have been treated as the main consideration. This paper describes the distribution characteristics of switching the surge voltage in the stator windings of an induction motor driven by IGBT PWM inverter. To analyze the voltage distribution between turns and coils of the stator winding, an equivalent circuit model of the induction motor including feeder cable is proposed and high frequency parameters are computed by finite-element analysis. From the electro-magnetic transient program (EMTP) simulation of the entire system, which consists of induction motor, feeder cable, and PWM inverter, the effects of rising time of the inverter output voltage, cable length, and switching frequency on the voltage distribution are also presented. A 380 V, 50 HP three phase induction motor with taps from the first through fifth turns has been built in order to experimentally measure the turn voltage and it provides informative experimental results.