The application of conductive and semi-conductive corona protection tapes to VPI'ed high voltage stator coils

Conductive tapes are used as a conductive layer on the coil slot portion to reduce corona discharges that can occur on the coil surfaces. Semi-conductive corona protection tapes are used on the coils at the slot exit region and prevents surface discharges at these locations. The use of these commercially available tapes on high voltage coils that are processed using the vacuum pressure impregnation (VPI) method, has been developed. Laboratory and factory tests were performed to determine the type of tapes to use, the application process, the required process steps, and the tape performance after coil processing. This paper reviews the successes and failures associated with the application of the commercial tapes and describes what does and what doesn't work when the tapes are applied to VPI stator coils. The design objectives and how the tapes meet or fail to meet these objectives are described. The test methods used to evaluate the tapes is presented along with the test data that summarizes the findings of this work.