Investigation of Partial Discharge Activity and Insulation Life of a Large Hydro Generator

Abstract

Partial discharge (PD) is a well-known indicator of an aging insulation system, so trending the PD activity is suggested as a tool to prevent insulation failures by targeted interventions. This paper presents a case study in which on-line PD measurements showed a significant increase over several years and triggered an investigation and repair plan. Off-line site tests confirmed the concerns and helped in locating and replacing the most vulnerable bars. Laboratory tests on the service-aged bars also provided valuable information about the root cause and insulation condition of the winding.