A suggested approach for specifying partial discharge testing as a new winding acceptance test

Partial discharge testing has been used for over 50 years as a diagnostic to assess the insulation condition of motor and generator stator windings rated 3.3 kV and above. As such, most of the North America´s large utility generators already undergo routine on-line PD testing. Many users have expressed a desire to specify allowable PD levels for new stators or rewinds-to ensure acceptable manufacturing and assembly of the winding, especially for global VPI stators. Unfortunately there are no domestic or international standards that describe the acceptable PD levels. If PD tests are to be used as acceptance tests-then the users must insert this in their purchase specifications. One must be very careful when specifying PD for a new machine-to ensure that the test is both meaningful, yet not unreasonably difficult to pass. This paper reviews the reasons for this, and proposes a scientifically defensible way of specifying PD, that is independent of the test equipment used