Experience with the partial discharge testing of operating motors and generators

Surveys have shown that about 40% of serious motor and generator problems are due to the deterioration of stator winding insulation. 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 insulation failure mechanisms. An online partial discharge test, called the TGA test, has now been specifically developed for turbine generators and large motors. The TGA test allows fossil and nuclear power plant staff to reliably perform a partial discharge test on motors and turbine generators. This paper presents several case studies of the use of this new partial discharge test technology on generators. 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 utilities to economically and reliably plan stator winding maintenance and avoid unexpected failures