A technique for defect investigation in pulse-controlled motors through partial discharge measurements

This paper presents a procedure for the investigation of partial discharge (PD) sources in PWM-controlled motors, based on off-line measurements under bipolar squarewaves. PD measurements were carried out on three-phase motors with open-star windings and different configurations, e.g., one phase supplied while the other two were grounded, two phases connected in series, grounding the motor frame. The voltage waveforms generated by a power supply and applied to motor windings was recorded at the winding terminals, for each test configuration. These measurements allowed to highlight winding positions where insulation can be overstressed by uneven voltage distribution, as occurs on motors in service. By comparing partial discharge measurement patterns along windings and under different test configurations, a qualitative evaluation of the location of partial discharge sources inside the tested motors was carried out.