Partial Discharge Measurement for Low- Voltage Motor Insulation Systems at Square Wave Voltage with Variable Slew Rate

In this work the dependence of the repetitive partial discharge inception voltage on the slew rate at square wave voltage is investigated. The partial discharge (PD) is measured with high frequency current transformers in combination with high pass filters and a wide band digital oscilloscope. A silicone carbide inverter is presented to generate the test voltage. The developed gate driver makes it possible to vary the slew rate. Twisted pairs are used as test samples, which are a possibility to represent the insulation system of the winding head of an electric motor. The results show that for unimpregnated twisted pairs a self-healing effect occurs, which is most likely due to the formation of space charges in the air winding. In comparison, the influence of the slew rate is rather negligible in the range considered.