Effects of motorette structure and vanish treatment on repetitive partial discharge inception voltage measurement test in inverter surge insulation

The Inverter surge is a high-voltage phenomenon that is generated by the overlap returning waves by impedance mismatching among an inverter, cable and motor. The inverter has been available by advancement of control system of electrical instrument, such as the industrial motor. Insulation performance evaluation technology by partial discharge (PD) measurement is important because the mechanism leading to breakdown by the inverter surge is a cause of PD. In this study, a design methodology for the impulse generator for partial discharge test is developed. In addition, we measure repetitive PD inception voltage (RPDIV) at phase to phase, phase to ground and turn to turn in a motorette sample using automatic RPDIV measuring system and developed repetitive impulse voltage generator. As a result, it is found that generated voltage and current waveform varies depending on the motorette structure. It is also found that RPDIV of the motorette differs with and a without a varnish treatment. The repetitive impulse voltage is applied to confirm the insulation dignity of inverter-fed motor insulation.