Application of partial discharge testing to motor and generator stator winding maintenance

Deterioration of stator winding insulation continues to be one of the predominant causes of large motor and generator failures. Over the past several years, practical methods have been developed for measuring the partial discharge activity in the high voltage insulation of stator windings, since partial discharges are a symptom of most of the insulation failure mechanisms in motors and generators rated 4 kV or more. The turbine generator analyzer (TGA) test has now been specifically developed to enable industrial plant staff to reliably perform a partial discharge test on operating motors and turbine generators. This paper presents several case studies of the use of these new partial discharge test technologies on rotating machines. Test results show that machines with deteriorated windings have a partial discharge activity at least 30 times higher than good windings. The availability of these test methods enables plant staff to economically and reliably plan stator winding maintenance, avoid unexpected failures and often extend the time between major maintenance outages.