Dielectric response of machine insulation extracted from DC ramp test on individual stator bars

DC ramped voltage testing is used to assess the condition of the stator windings in high voltage generator stator windings. When used to only assess the ability of an insulation system to withstand a predetermined DC voltage level, the continuous (and usually slow, typically in the order of 1 kV/min) increase in applied voltage combined with the continuous monitoring of the current often allows a better control of the test to avoid unexpected failure and damaging the insulation. In addition, it can also be used as a diagnostic test and can provide quantitative information similar to the IR/PI test. This paper presents DC ramp test data from individual bars as well as the calculation techniques to calculate the insulation dielectric response compares it to results from polarization depolarization current (PDC) tests.