Diagnosis of stator insulation of generators and motors using in-service partial discharge testing

This paper presents a practical partial discharge (PD) measurement system to diagnose stator insulation problems of generators and motors under normal machine operation. Partial discharge analyzers (PDA) can identify the type, nature, area and severity of partial discharge activity in the stator winding and associated problems (e.g. winding looseness). It is well known that heavy interference noise in on-line PD measurement may give a false indication of the insulation condition and hence reduce the confidence of users. The PDA system uses a pulse-by-pulse noise rejection technique to eliminate noise in operating generators and motors and to ensure reliable PD data acquired. The PDA system, the noise rejection technique, data analysis, and some practical PDA testing cases are presented.