ELECTRICAL STRESSES APPLIED TO STATOR INSULATION IN LOW-VOLTAGE INDUCTION-MOTORS FED BY PWM DRIVES

The authors report experiments to identify real voltage stresses appli ed by pulsewidth modulated (PWM) variable-speed drive on the stator in sulation of a low-voltage induction motor, The idea that PWM drives im pose very high stresses on machine parts, especially the insulating ma terial, is widely accepted. Many theories and simulations have been ca rried out on the subject for nearly a decade, but too few experimental confirmations have been undertaken. The authors have processed a stan dard motor to access the copper wires inside the stator winding, Obser vation of real electrical stresses applied to insulation was performed thanks to these tapping points. The ground insulation is first identi fied putting in value the inductive effect of winding and the complexi ty of the three-phase voltage combination at the star point, Monitorin g of the voltages applied to interturn insulation reveals much higher surges than expected. Finally, the impact of PWM drives on insulating material is discussed with reference to the resulting experimental dat a.