A variety of diagnostic tests are widely applied in the field in industry to evaluate the condition of high voltage (HV) motor stator insulation. In this paper, the influence of temperature on the stator insulation diagnostic tests such as the insulation resistance, AC current, dissipation factor, and partial discharge measurements are studied and reported. The tests are performed with the HV motor stator winding temperature set between 40℃ to 80℃ in 10℃ intervals. It is shown that the AC current, dissipation factor, and partial discharge magnitude steadily increase with temperature, which suggests that temperature must be taken into account in the interpretation of the test results.

Insulation breakdown of water-cooled generator stator windings occurs frequently due to leakage of cooling water and absorption into the insulation material. Leakage and absorption problems of water-cooled stator windings are often found during regular preventive maintenance. To evaluate cooling water leakage and absorption, diagnostic tests were performed on two water-cooled turbine generators, which have been in service for 13 and 17 years, respectively. The test results of the measured electrical properties such as dissipation factor (tano), capacitance and AC leakage current for water-cooled generator stator windings with wet bars are reported in this paper.