Improvements in Direct Current Stator Winding Insulation Testing

Direct Current (DC) high voltage testing is frequently used to assess the condition of stator windings. The list of the reasons why DC tests may be preferred over alternating 50 Hz or 60 Hz voltage tests is long: smaller size of the test equipment, fewer partial discharges, less risk of damage in the case of very poor insulation quality. Different direct current test methods are possible such as DC HIPOT, polarization index test, ramped voltage test, uniform time and graded time voltage step test, insulation profiling, etc. Since the traditional DC hi-pot test is not a diagnostic test (the result of the test is either PASS or FAIL), an improved method of DC testing using ramped direct high voltage was introduced by Bruce McHenry in 1964 [6] and this paper describes the differences between the two ramped direct-high voltage methods proposed in IEEE 95.