Motor & generator high voltage AC testing over voltage coil testing: Withstand & qualitative diagnostics explored

There are many tests made to a motor or generator at various steps along its production and upon completion, when Acceptance tests are conducted. For medium voltage input coils like 2.4 kV, 4.16 kV, 13.8 kV, etc., testing during and after winding or repair with high voltage is one of many recommended, really essential, tests to verify the integrity of the coils. Off-line, elevated over voltage testing (>Uo) should be part of any testing program. Many use AC voltage, many use DC voltage, and many do not perform any over voltage testing. Who's right, who's wrong, and what are the considerations? This paper provides a brief overview of the commonly performed over voltage tests, explains why AC voltage should be used and not DC, and describes the test equipment options with a guide to selecting the proper high voltage equipment.