Examples of stator winding partial discharge due to inverter drives

Random wound stator windings in motors have failed when exposed to the fast-risetime voltage surges coming from inverters. Measurements on motors show that these surges can create partial discharges and these discharges eventually destroy the turn-to-turn and/or phase-to-phase insulation, resulting in premature motor failure. Since the risetime of the voltage surges is in the same order of magnitude as the risetime of the PD pulses themselves, it is very difficult to separate the PD from the surges. Thus there has been little characterization of the PD caused by IFDs. Using a new device that can separate the PD from the surges, preliminary measurements of discharge inception voltage from several different motors, as well on twisted pairs of magnet wire were made. The DIVs under surge voltage are significantly higher than those made with 60 Hz voltage. As expected, the PD magnitude increases dramatically with applied surge voltage. PD pulses occur during a small percentage of the surges.