Detection of partial discharges on the online hydro-generator stator winding

Abstract

Demand for hydro power is ever increasing with the escalating cost of fossil fuel and generation capacity limitations at peak loads. Therefore availability of hydro units is critical in order to cater the demand. The insulation system of stator winding is highly susceptible to electrical, thermal and mechanical stresses, aging and consequent failures. Replacement or maintenance of Stator winding would take long time and properly engineered condition monitoring system is needed to avoid such occurrence or plan remedial works making outage time minimum. Off line test methods has long been used to assess the condition of the motor and generator winding insulation. There are practical limitations in those methods while Online Partial Discharge (PD) measurements is currently being used commercially addressing some of the drawbacks of offline methods. This research analyses the 2 different online PD monitoring technologies which are being commercially used for hydro generators. Required data were obtained from the PD monitoring systems installed at Samanalawewa Hydro Power station. Pulse distribution patterns of PD with respect to polarity predominance, Load effect on PD, effect of environmental factors of humidity and temperature on PD, cross talk between phases when measuring PD and applicability of RTDs embedded in the winding to sense PD were analysed. Results have been interpreted based on the obtained data and contemporary research works on online PD monitoring systems.