Stator winding performance testing when using AC and DC voltages

This paper is written on the basis of recommendations in IEEE Std 95-2002. This is a follow up paper written and presented at 2005 EIC. It is common practice to use both AC and DC power supplies for the high potential testing of large electrical generator stator windings. A much higher voltage, well above the machine operating voltage; is almost always used. This paper reviews the procedures, results and test aspects of both the AC and DC testing of stator coils and the completed stator winding. The major issues addressed are the voltage levels used; where and when they are applied; the relationship between the AC and DC test voltage levels; what components of the winding are actually being tested; what temperatures are experienced when testing; and are the presently used multiplication factors between DC and AC really being used correctly. A significant issue to address is that the stator coils and the stator winding layout, is designed to primarily get through the final AC or DC hi-pot test. It will be shown what the coil end turn grading response is when tested with DC and AC voltages.