Internal partial discharge and breakdown characteristics of thin polypropylene films

The effect of cavity dimensions such as diameter (0.9 mm to 3.2 mm) and depth (40 /spl mu/m to 200 /spl mu/m) on the various PD (partial discharge) characteristics and the related breakdown of thin PP (polypropylene) films was studied experimentally. The inception voltage is found to increase with decreasing cavity diameter for a given depth and with increasing cavity depth for a given diameter. Measurements of discharge magnitudes indicate that a single discharge does not completely discharge the entire cavity. The discharge pulse magnitudes, number, and distribution depend on the diameter as well as the depth of the cavity. Experimental and calculated values of maximum discharge magnitude for different diameters and depths of the cavity indicate that there is an increasing deviation between the calculated and experimental values as the cavity diameter increases. This implies that only a part of the cavity and not the whole of discharges.<>