Use of AC and DC hipot tests to assess condition of stator insulation

Many generating stations in North America are more than 25 years old and are being refurbished to extend their serviceable life. Condition assessment of stator insulation in motors and generators is an important part of the life extension process for the generating stations. Various electrical tests including AC and/or DC hipot tests are used to determine whether the stator insulation is in serviceable condition, or should be refurbished or replaced. However, the equivalence of the AC and DC hipot tests or superiority of the one over the other in finding weak spots in the insulation has been a subject for discussion for many years. This paper provides experimental data for determination of the relationship between AC and DC hipot tests.