A Utility's Functional Evaluation Tests for High-Voltage Stator Insulation

This is a progress report on research projects conducted in co-operation with the AIEE Rotating Machinery Insulation Subcommittee, the Canadian Electrical Association's Apparatus Section, and individual manufacturers and utilities. For the functional evaluation required by a utility, a voltage-endurance test was chosen as most indicative of the ionization resistance which is considered critical in short-bore water-wheel generators, and a test of endurance of the mechanical effects of thermal cycling was chosen as most applicable to the critical qualities of insulation for steamturbine generators and other long-bore machines. Test equipments of moderate size and cost have been developed for voltage and mechanical endurance. Emphasis has been laid on close control of aging influences; variation of voltage test "lives" of similar samples has been reduced to within a ratio of three to one. The voltage-endurance equipment is finding further use in studies of effects upon insulation life of various dry-out, overvoltage testing, and operating practices. The mechanical-endurance tester is being used in a study of the optimum clearances between coil side and slot for various insulations.