A Turn Insulation Test for Stator Coils

Normally applied maintenance tests do not evaluate the condition of insulation between the turns of generator coils. The existing standards recommend neither methods of turn insulation testing nor values of voltage for testing turn insulation. This situation exists in part because of the difficulty in applying a proper test voltage to the turns without overstressing the ground insulation. Occasions arise, particularly with large hydro generators, where it is necessary to either test the turn insulation to assess the quality of the coils in a stator winding or else to completely rewind the machine.