Investigation of the effect of humidity on partial discharge activity in stator windings

Recent investigations using continuous on-line partial discharge (PD) monitors on operating rotating machines have indicated that the PD activity may be strongly affected by humidity and/or dew point. The humidity dependence seems to be associated with specific stator winding deterioration processes such as electrical tracking and endwinding PD. Laboratory experiments have been designed and conducted to simulate these failure processes, and determine the effect of humidity and temperature on the Partial Discharge Inception Voltage (DIV), under power frequency conditions. This paper presents the results of the experiments. As well, the results obtained under laboratory conditions are compared to on-line PD data acquired on a motor and the results are discussed. The results indicate that the absolute humidity, rather than the relative humidity, need be considered when evaluating the influence of humidity on PD activity. Furthermore, the results indicate that the two mechanisms may be dominating the influence of humidity and temperature on DIV.