Initial experience with quadratic rate partial discharge tests on the stator winding insulation of power generators in South Africa

The Electricity Supply Commission of South Africa (Eskom) and Electricite de France (EDF) are involved in a technical exchange agreement whereby the effectiveness of the EDF method for stator winding insulation condition assessment, specifically on turbogenerators, will be investigated. This method basically entails off-line electrical quadratic rate partial discharge measurements, using relatively low center-frequency narrow band filters. Initial experience gained through measurements on two turbogenerators of Eskom in South Africa, has shown the ability of this method to accurately indicate the insulation condition of stator windings. On one of the generators tested, excellent correlation was found between the indications of test results and the findings of a stator bar visual inspection and dissection. Dissipation factor and conventional peak-value partial discharge measurements have in the past failed to indicate the extend of insulation damage (discovered through visual inspections) of this specific winding