PD activity in void type dielectric samples for varied DC polarity

This paper discusses the DC testing of a dielectric sample (with voids) under DC conditions. The ramp test method was employed to assess whether the tests were repeatable. Three DC ramp tests were performed in quick succession. The polarity of the first/third tests was positive and the polarity of the second test was negative. The resultant partial discharge activity was analyzed for each series of tests and compared for positive and negative conditions. The results show that the inclusion of a negative ramp between two positive ramps enabled similar PD activity to be recorded in the first and second positive ramp tests. The negative cycle was used to re-initialise the test sample and allows trapped charge to migrate enabling similar PD activity in the subsequent positive ramp test. Changes in PD behavior were observed in the distribution of PD data between the tests.