Partial discharge testing of random wound stators during short risetime voltage surges

Modern inverter fed motors often produce short risetime, high magnitude voltage surges that may lead to partial discharge in the random wound stator windings. Detection of PD during such voltage surges can not be done with the usual PD detectors described by ASTM D1868. Instead a detector that can separate PD pulse currents from a short risetime voltage surge is required. This paper describes a PD detector that can measure PD pulses when the applied voltage is a voltage surge with a risetime as short as 100 ns. PD data has been collected from dozens of stators, many of which had known insulation problems. In most cases the PDIV easily met the requirements of a new IEC technical specification that sets the partial discharge inception voltages for random wound stators. Since most of these stators had obvious insulation system deficiencies, it seems that the PDIV levels set by IEC TS 60034-18-41 may be too low.