Effect of HVDC stress on breakdown strength and partial discharge activity of lapped thin film insulation

In this paper results from measurement of electrical breakdown strength and partial discharge activity of samples comprised of polypropylene films is presented. Breakdown testing of 1-film samples using a linearly increasing voltage shows that the breakdown strength is reduced by 15% in the temperature range from 20 to 100/spl deg/C. Impulse breakdown testing of 1- and 5-film samples show that the 1-film samples have significantly higher breakdown strength. Prestressing with 50 and 150 kV/mm result in reduced breakdown strength for both aiding and opposing polarities for 1-film samples, whereas no effect is observed for the 5-film samples. Measurement of partial discharge activity of samples with an artificial void of varying diameter, show that the discharge activity is dependent on the area of the void and on the time of voltage application.