Measurements of slot partial discharges with an antenna during accelerated aging

A long-term aging experiment is currently under way on six stator bars subjected to slot partial discharges (PD) activity under electrical, thermal and mechanical stresses. Slot PD were induced on each bar by abrading a portion of their semi-conductive coating. All bars were subjected to accelerated aging at twice their nominal voltage. Two bars were only electrically stressed, two others were electrically and thermally stressed and the last two were electrically, thermally and mechanically stressed. It was noted that the evolution of slot PD was different for each kind of stress. In order to understand those differences, periodic measurements as a function of the aging time were conducted using a directional antenna to detect the electromagnetic radiated signal from each specific slot PD site. The results show the evolution of slot PD activity for the different stress conditions.