A comparison with insulation system for PWM-inverter-fed induction motors

The winding insulation of low-voltage induction motors in adjustable-speed drive system with voltage-fed inverters is substantially stressed due to the uneven voltage distribution and excessive voltage stress (dv/dt), which result in the premature insulation breakdown. This paper describes test results of the insulation characteristics from 20 HP, 380 V induction motors for inverter applications. Five different types of insulation techniques are applied to 19 induction motors. The insulation characteristics are compared to partial discharge, capacitance, AC current, and dissipation factor tests. Also, the insulation breakdown tests by high voltage pulses are performed, and the corresponding breakdown voltages are obtained.