EXISTENCE OF PARTIAL DISCHARGES IN LOW-VOLTAGE INDUCTION MACHINES SUPPLIED BY PWM DRIVES

When standard low voltage induction motors are supplied by pulse-width modulated (PWM) adjustable speed drives, some of the traditional sinu soidal system concepts cannot be applied. This paper reports the resul ts of an investigation of the effect of PWM drives on the insulation o f the stator winding. The characteristics of the employed dielectric m aterial and the magnitude of the applied voltages led to the hypothesi s of the possible existence of partial discharges within the insulatio n. Practical experiments were carried out and high frequency signals w hich could be associated with such a phenomenon were observed. These m easurements also showed that the interturn insulation undergoes some h igh electrical. stresses and that the nominal rotation speed (50 Hz) a ppears to be a point of high disturbance in the working of the motor. Further work is required, since most of the points identified here nee d to be understood fully.