Partial discharge measurements on hydro generator stator windings case studies

An overview is given of four case studies of four dominant partial discharge (PD) activity types in generator stator windings, including measurements and data analysis. The PD analysis considered the PD pattern, polarity dominance, and pulse phase analysis (PPA) in correlation with visual inspections and high-voltage testing. The four PD cases are as follows: PD within the groundwall insulation, confirmed by conducting dissipation factor tip-up and corona probe tests; PD at the end of a slot, confirmed by removing the bars from the slot; PD at winding end-turns, confirmed through a blackout test and visual inspection; and PD at the stress control grading paint area, confirmed by visual inspections.