Study of epoxy/mica insulation deterioration in generator stator using ultra-wide band partial discharge testing technique

The epoxy/mica insulation in a generator stator deteriorates under the conditions of thermal, electrical, vibrational and thermo-mechanical stresses when the generator is running. To assess the insulation aging status and to understand the deterioration process, an ultra-wide band partial discharge testing method was adopted in this study. A multi-stress accelerated aging equipment was established to imitate the actual service conditions. Obvious change in the waveforms of discharge pulses was observed when the epoxy/mica insulation was under accelerated aging condition in the laboratory. The test results indicated the formation and growth of voids in the insulation during the aging process. Furthermore, optical microscopy and SEM were used to examine the insulation. Delamination and cracks in the insulation were observed which accorded with the ultra-wide band partial discharge test results.