Generation and Dissipation of Negative Heterocharges in XLPE and EPR

Charge generation in cross-linked polyethylene (XLPE) and ethylene propylene rubber (EPR) under dc stress are influenced strongly by inclusions. The inclusions influencing charge generation are cross-linking byproducts, antioxidants, and moisture. These inclusions particularly influence the generation of negative heterocharges observed near positive electrodes, which produce high electric stress regions in XLPE cable insulation under dc voltage. Because a high electric field might cause dielectric breakdown of high-voltage equipment, it is important to minimize negative heterocharge accumulation. Consequently, the authors performed experiments to clarify the negative heterocharge generation mechanism in XLPE and EPR. The authors first studied the influence of cross-linking byproduct and moisture on negative heterocharge generation to clarify the mechanism. The authors next performed experiments to elucidate the effect of antioxidants on heterocharge generation, which revealed that the negative heterocharge is generated in XLPE insulation containing sulfur-containing phenolic antioxidant, or sulfur-type antioxidant. This heterocharge is presumed to be created by the combined effect of the antioxidant and acetophenone. Furthermore, the authors studied the dissipation of negative heterocharges in XLPE and EPR, clarifying that the dissipation of negative heterocharges in EPR is much faster than that in XLPE. This paper presents results of these studies.