A THERMAL CYCLING TYPE TEST FOR GENERATOR STATOR WINDING INSULATION

Virginia Power has decided to replace the existing stator windings of the six hydraulic turbine generator-motors at its Bath County Pumped Storage Station, due to premature, severe degradation of the groundwall insulation system. As part of the vendor selection process for the manufacture and in-situ replacement of these windings, a 'Vendor Qualification Program' has been instituted. Ten fully-rated sample bars (half coils) furnished by each of three pre-qualified vendors are being subjected to accelerated aging tests at Ontario Hydro's Research Division facility. These accelerated aging tests will determine the relative ability of the replacement windings to resist deterioration and withstand actual operating conditions. A novel aspect of the program is a thermal cycling test which simulates the aging which the stator insulation system can experience due to severe cyclic duty. In addition to being used for pumped-storage generators, the thermal cycling test may be useful to evaluate the insulation system in combustion turbine generators. The thermal cycling test identified different manufacturer's insulation systems which were more able to resist deterioration due to peaking operation.