Steep-fronted impulse voltage testing of machine stator coils

The characteristics of steep-fronted voltage transients generated by switching operations in cable connected motor systems are described. It is shown that such transients produce severe interturn insulation stresses in machine windings. Factors which need consideration when drafting the necessary test standards for ensuring that interturn insulation will withstand such severe stresses are discussed. Techniques necessary for the correct implementation of such standards are explained. Results of interturn insulation tests on the coils of a large induction motor are presented and it is shown that steep-fronted transients voltage tests may be readily carried out if due care is taken in the test procedure.