What Medium and High Voltage Stator Winding Partial Discharge Testing Can - And Can Not - Tell You

Off-line partial discharge testing has long been used as a quality control test for the stator winding insulation in motors and generators rated 6 kV and above. Both on-line and off-line PD tests are widely used to assess the condition of the insulation to determine if maintenance is needed. Although there have been many papers published on successful PD tests where stator winding insulation problems were detected, this paper tries to point out some of the limitations of PD testing that we have learned over the years from over 18,000 machines. In particular, the issue of false positive indications and false negative indications is discussed, with several examples presented.