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Inhibition of Rejuvenation Liquid on Trees in XLPE Cables under Switching Impulse Voltages

In this paper, the inhibitory effect of preinjected rejuvenation liquid on trees in cross-linked polyethylene (XLPE) cables was investigated. Experimental samples were prepared by inserting needles into XLPE samples, and many equally-spaced holes existed in the outer semiconductive layer. All cable samples were divided into two groups. One sample group was treated with rejuvenation liquid, while the other group was the control group. A tree accelerated aging system was used to obtain trees in the XLPE cable samples. During the aging experiment, an impulse voltage was applied to the samples repeatedly. The micromorphologies of the two groups were observed. Based on the micromorphologies, two parameters were determined: the initiation rate of electrical trees and the average length of trees. Furthermore, the electric field distribution was simulated to analyze the initiation of electrical trees. The results indicate that an electrical tree is much harder to initiate in the pretreated XLPE cables than in the untreated cables. This phenomenon is likely attributed to the dielectrophoretic forces in the pretreated cables. Moreover, rejuvenation liquid deposited in XLPE causes a substantial reduction in the Maxwell stress of molecular chains. Rejuvenation liquid inhibits electrical tree initiation and water tree growth to a great extent.