Aspects of electric charge on the surface of polymer materials in gas filled gaps

The number of discharge sites and butt gap stresses for a 10 pC discharge magnitude have been measured for a 1 mm diameter void in the middle layer of a 3 layer sample in a 3 mm gap between electrodes in air, nitrogen and helium at atmospheric pressure and temperature. In tests on tapes from cable models the maximum charge density was found in the butt gap areas. Nitrogen has the highest breakdown strength and gives a lower number of discharge sites than helium and air. Valeron is seen to be the best discharge resistant material followed by polypropylene, HDPE, Nylon, Melinex, polycarbonate and Kapton H. However, the butt gap stresses for 10 pC and number of discharge sites apply in magnitude to these materials in the reverse order