Partial discharge activity in high voltage stator coils

Partial discharges (PD) within the insulation components of high voltage stator coils can cause damage over a period of time and can have a detrimental effect on such coils. Possible internal locations of PD in a stator coil are the groundwall insulation; the Roebel filler material; and between the interface of the uninsulated bar and groundwall insulation. Of these three, it was found that Roebel filler can be the largest contributor to PD activity. This paper describes the testing and analysis that was done on experimental high voltage coils in order to obtain a better understanding of PD activity within the coil´s insulation system. Results are presented that show how corona probe measurements and power factor tip-up measurements were used in the detection and analysis of PD activity within a high voltage coil. The major factors that contribute to high levels of coil PD are presented, along with ways to reduce PD