EXPERIENCE WITH ON-LINE PARTIAL DISCHARGE TESTING OF MOTORS AND GENERATORS

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. One test, called the PDA test, can be performed by utility personnel during normal operation of a hydrogenerator. Several improvements have recently been made to the PDA test to help maintenance personnel interpret results and identify the root cause of any problems. A similar 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 plant staff to reliably perform a partial discharge test on motors and turbine generators. This paper presents several case studies of the use of these new partial discharge test technologies 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.