Partial discharge screening test for internal voids and delaminations in stator coils and bars

Beginning in 1989 a partial discharge screening test was applied to stator coils and bars for which the measuring frequency bandwidth was approximately 8 MHz to 100 MHz. In this frequency range, the measurement is more sensitive to partial discharges in internal voids and delaminations than is the case for discharges associated with surface coatings. Recently changes have been made to the test circuit which have improved the repeatability of the measurement. Selection of the operating voltage for particular stator coils and bars based on their partial discharge screening test results may reduce the risk of future problems with the winding