Impact of Temperature on Partial Discharge in Generator Stator Windings

Partial discharge (PD) diagnosis is widely used to assess the insulation condition of generator stator windings during operation. However, the influence of winding temperature on PD behavior remains insufficiently understood. This study investigates the temperature dependence of PD characteristics in the epoxy/mica-insulated stator windings of hydrogenerators. To elucidate this dependence, PD measurements are performed on two operating hydrogenerators and three types of coil bars at sample temperatures ranging from approximately 25 °C to 90 °C. The results show that the phase-resolved PD patterns of void discharges are unaffected by sample temperature. By contrast, the largest repeatedly occurring PD magnitude (Qm) increases or decreases with the temperature of the sample, depending on the degree of insulation degradation. A strong correlation is observed between the temperature dependence of Qmand the breakdown voltage of the coil bars. Based on these findings, this study provides a proof-of- concept diagnostic approach that utilizes the temperature dependence of Qm.