DC tree and grounded DC tree in XLPE

To elucidate the effects of antioxidants on electrical trees generated by DC voltage (DC tree) and trees generated by grounded DC voltage (grounded DC tree), experiments were performed using XLPE samples containing phenolic and sulfur-type antioxidants. Results of the experiments showed that, in all XLPE samples, positive DC trees were generated at lower voltage than the negative DC trees, whereas grounded positive DC trees were generated at higher voltage than the grounded negative DC tree. Experimental results showed also that XLPE samples containing sulfur-type antioxidant exhibit higher DC and grounded DC tree inception voltages. Taking account of the amount of injected charge from electrode tips, the polarity effect of the DC tree and grounded DC tree were examined. Effects of the antioxidant on the DC trees and grounded DC tree were also examined. It was presumed that enhancement of the charge injection by antioxidant from the needle electrode is responsible for DC tree suppression, whereas the charge trapping effect by antioxidants is thought to be the reason for tree suppression of the grounded DC tree.