Motor Winding Problems Caused by Inverter Drives

FOR OVER 70 YEARS, RESEARCHERS have understood that fast rise-time voltage surges from a circuit breaker closing can lead to an electrical breakdown of the turn insulation in motor stator windings [1]. If the turn insulation is of an insufficient thickness or has aged in service, the insulation will puncture when a short rise-time voltage surge occurs. Punctured turn insulation allows for a very high circulating current to flow into the affected copper turn, rapidly melting the copper conductors, which, in turn, results in a consequent burning/melting of the slot liner insulation, thus leading to a stator winding ground fault [2], [3].