How humidity affects partial discharge activity in stator windings

It has been found that PD activity may be strongly affected by humidity and/or dew using continuous on-line partial discharge (PD) monitors on operating rotating machines. This appears to be associated with specific stator winding deterioration processes such as electrical tracking and end-winding PD. Experiments have been conducted to simulate these failure processes, and to determine the effect of humidity and temperature on the partial discharge inception voltage (DIV), under power frequency conditions. This paper illustrates the results of these experiments. As well, the results are compared to on-line PD data acquired on a motor. The results indicate that the absolute humidity, not relative humidity, need be considered when evaluating the influence of humidity on PD activity. The results also indicate that the two mechanisms may be dominating the influence of humidity and temperature on DIV.