WGC1 - Substations Working Group C1

Suggestions are made for testing the dielectric strength of the insulation separat­ing the various turns from each other within multi-turn form-wound coils to determine their acceptability. Typical ratings of machines employing such coils normally lie within the range of 200 kW to 100 MW. The test voltage levels described do not evaluate the ability of the turn insulation to withstand abnormal voltage surges, as contrasted to surges associated with nor­mal operation. The suggestions apply to: (1) individual stator coils after manufacture; (2) coils in completely wound stators of original manufacture; (3) coils and windings for rewinds of used machinery; and (4) windings of machines in service to determine their suitability for fur­ther service (preventive-maintenance testing). Coil service conditions, test devices, and test sequence are discussed. Surge test levels for new coils during winding and for complete windings are given.