A novel approach to identify slot discharges in the presence of end winding corona discharges

Different types of partial discharges occur in stator winding insulation and a few partial discharges may occur simultaneously. Among them, one of the important discharges, i.e. slot discharge, may get masked in the presence of end winding corona discharge. In such cases, recognizing the occurrence of slot discharge during partial discharge measurements is a challenging task. Therefore, in this paper, a novel approach has been used to identify the slot discharge in the presence of end-winding corona discharge. This approach is based on partial discharge measurements at 50 Hz and at a low frequency, in particular 0.1 Hz. Similar phase resolved patterns were seen at 50 and 0.1 Hz, for both discharges. In this method, per cycle positive integrated charge is measured and is compared at different PD threshold values. This unique method of determining the integrated charge as a function of PD threshold value clearly indicates the existence of slot discharges in the presence of end winding corona discharge. Otherwise, the occurrence of slot discharge would have gone unnoticed if the measurements were carried out only at power frequency, as it is usually done.