Analysis and localization of spurious partial discharge activity in generator units

Partial discharge (PD) measurements are an effective tool to assess the condition of important power plant components, such as the generator, the generator circuit-breaker and the step-up transformer.This paper shows that, in addition to phase-resolved patterns, the waveshapes of PD signals provide valuable information on the type and origin of the discharges. The authors describe the complex propagation of PD signals in a stator winding and the consequences for PD detection. Results from on-line measurements in three power plants where abnormal PD activity was observed are presented. In all cases the source of the PD's ccan be located: (i) slot discharges in a 125 MW generator, (ii) interphase discharges in the end-windings of a 165 MW generator, and (iii) an improperly installed bleeding resistor in a generator-circuit breaker.