On-line monitoring for condition assessment of motor and generator stator windings

Deterioration of the stator windings continues to be one of the predominant causes of large motor and generator failures. Over the past several years, much research has been done to develop technologies to provide plant maintenance personnel with better, more objective methods of assessing the condition of machine windings. Through this work, 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 major insulation failure mechanisms. One test, called the PDA test, has been successfully used by utilities for many years, and can be performed by plant maintenance personnel during normal operation of a hydrogenerator. A similar partial discharge test, called the TGA test, has now been specifically developed for turbine generators and high voltage motors and is described in this paper. The TGA test allows motor and generator users of machines rated 4 kV and above, to reliably perform an in-service partial discharge test and through interpretation of the test results to confidently assess stator winding condition and plan machine maintenance requirements. Since the test is done by plant personnel during normal motor or generator operation, testing costs are also very low