Effects of Phenolic and Sulfur Type Antioxidants on Polymeric Dielectrics

This study examined the effect of phenolic and sulfur type antioxidants on thermal and electrical deterioration of polymeric dielectrics, as well as the charge trapping effect under DC voltage stress. We confirmed that the sulfur-containing phenolic antioxidant 4,4´-tiobis (3-methyl-6-tert-butyl phenol) inhibits thermal degradation of ethylene propylene diene monomer (EPDM). Experimental results of cross-linked polyethylene (XLPE) demonstrated that phenolic and sulfur type antioxidants clearly suppress AC tree initiation. A synergistic effect between a phenolic antioxidant and a sulfur-type antioxidant was confirmed. It was presumed that the radical trapping effect of the antioxidant is responsible for inhibition of thermal degradation and tree initiation. Experiments on a grounded DC tree, and high-field conduction, were performed using XLPE samples containing phenolic and sulfur-type antioxidants to elucidate the effects of antioxidants on polymeric dielectrics under DC voltage stress. Results showed that samples containing sulfur-type antioxidants exhibit higher grounded DC tree inception voltages. The smaller conduction current was confirmed through flowing in XLPE which contains sulfur-type antioxidants. The charge trapping effect by antioxidants is the reason both for the increase of tree inception voltage of the grounded DC tree and the decrease of conduction current in XLPE