The electric stress from fast front repetitive pulse voltages on the winding insulation in a pulse width modulated (PWM) inverter driven induction motor is much more severe than that from conventional sinusoidal voltages. Partial discharge can be the result of voltage overshoots that are due to fast rise pulse, and dielectric heating may occur locally due to harmonics in pulse surges, which have proved to be detrimental to organic insulation. Therefore, when designing an insulation system or selecting a winding insulation for an inverter-duty motor, one has to consider the hazards of partial discharge, dielectric heating in addition to that of thermal, mechanical and environmental stresses.
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