Effect of surge testing on unimpregnated ground insulation of VPI stator coils

The IEEE 522 guide for testing turn-to-turn insulation in form wound coils for alternating-current machines is currently under working group review, with the intent to eliminate problems in interpretation and application. The guide is written for the testing of fully processed coils, while the motor industry uses the test guide for pre-impregnated vacuum-pressure-impregnated coils wound in the stator core. The impact of applied surge voltages on the ground insulation was investigated using finite-element analysis of stress and testing on actual coils. This paper presents data on surge testing of turn and ground insulation, and discuss some ideas on the use of surge voltages as a quality assurance test.