Voltage Stress Modeling and Measurement for Random-Wound Windings Driven by Inverters

This paper studies voltage stress in complex machine windings under steep-fronted voltage excitations from inverter drives. Electrical stress in this paper includes voltage overshoots between any two conductors in windings and between conductors and the stator. This stress can accelerate insulation degradation in inverter-fed machines compared to that in traditional ac machines. A high-fidelity finite element (FE) model is used to model individual conductors and parasitic parameters of the complex winding structure. The model is able to predict voltage stress between any two conductors or between a conductor and the stator ground wall during switching transients. The winding structure studied in this work is random wound and has multiple serial coils and multiple parallel strands. Both behaviors of single-phase windings and three-phase windings under Pulse Width Modulation (PWM) excitation were simulated to study the voltage stress on the stator insulation system. Experimental tests were performed to verify the FE modeling. Measured voltage distribution and voltage stress agrees with FE simulated results very well.