Common Questions on Partial Discharge Testing: A Review of Recent Developments in IEEE and IEC Standards for Offline and Online Testing of Motor and Generator Stator Windings

Partial discharges (PDs) are small electrical sparks that occur in voids within electrical insulation or on the surface of motor and generator stator winding coils. Offline and online PD testing have become widely used tools for in-factory quality acceptance and baseline performance evaluations of new groundwall insulation in stator windings rated 6 kV and above. Many petrochemical plants and refineries perform online PD tests to periodically assess the condition of the statorwinding insulation on machines during operation. The IEEE and the International Electrotechnical Commission (IEC) have created standards that are called recommended practices or technical specifications (TSs) to address offline and online PD measurement using electrical diagnostic equipment and optical measurement of surface PDs. The standards explain testing objectives and principles, discuss commonly used methods for measuring PDs, and provide guidance for data interpretation.