Effect of humidity on partial discharges of generator stator

Abstract

It was observed that the insulation condition of some generators is not up to the standard level when analyze the results of condition monitoring tests done on hydro generators of CEB. This situation prompted generator insulation level to be monitored closely. Hence, the Asset Management Hydro Electrical Branch of CEB recently initiated online monitoring of partial discharge (PD) activity in hydro machines. Partial discharge can cause progressive deterioration of insulation and end result of which may be eventual breakdown of the insulation. If partial discharges can be controlled to a certain level, possibility of unexpected winding failures can be reduced and loss of outages and repair cost can be avoided and the reliability level of the generators can be increased. Majority of main hydro power generators of Sri Lanka have been constructed in wet zone with water present lower close below the generator. Therefore these factors can give rise to higher humidity levels around such generators. The purpose of this research was to investigate the effect of humidity on partial discharge in hydro generators. For this study New Laxapana Unit 2 generator was selected and a partial discharge monitoring system was installed for online monitoring facilities. Using the data extracted from this system, behavior of PD variations against relative humidity was analyzed. In addition to that using an experimental setup PD activity was measured under controlled humidity conditions. Both these analyses confirmed that there is an effect of humidity on PD activity. Keywords: partial discharge, epoxy, mica