STUDY OF SPACE-CHARGE EFFECTS ON DIELECTRIC-BREAKDOWN OF POLYMERS BY DIRECT PROBING

Direct and quantitative probing of space charge was carried out to study effects of space charge on dielectric breakdown of polymeric insulating materials. In poly-p-phenylene sulfide, in which dielectric-breakdown characteristics were explained in terms of space-charge formation, positive homo space charge was observed. The amount and the depth of space charge detected could explain the dependence of impulse breakdown strength on prestressing both qualitatively and quantitatively. In oxidized polyethylene, negative homo space charge was observed. This also agreed well with the prestress dependence of the breakdown characteristics. The injecting electrode during the prestressing or the region nearby was suggested to be important in the breakdown process of both materials.