Proposal of Management Method for Stator Winding of Hydro Generator by In-service Partial Discharge Diagnosis

In diagnostics of insulation degradation of stator winding of hydro generator, a high voltage (HV) is applied to the stator winding by HV applying device while the generator is disconnected from the power system to diagnose the degradation state of the stator winding. A method for estimating dielectric strength from the result of the off-line diagnosis is in practical use. On the other hand, in-service partial discharge (PD) diagnostics, which measures and evaluates the PD generated from the stator winding in service, do not require HV applying device and allows the frequency of measurement to be set freely, making it possible to determine the deterioration trend of winding and to expect early detection of winding faults. However, in-service PD diagnostics for stator windings of hydro generators have not been sufficiently implemented in Japanese electric power companies. Therefore, we examine the applicability of in-service PD diagnostics and propose management method for stator winding of hydropower generator by in-service PD diagnostics.