Electrical treeing (ET) can irreversibly deteriorate the insulation of polymeric power cables\nleading to a complete failure. This paper presents the results of an experimental investigation into\nthe effects of unipolar and polarity reversing DC voltages on electrical tree (ET) and partial discharge\n(PD) behavior within high voltage direct current (HVDC) cross linked polyethylene (XLPE) cable\ninsulation. A double needle configuration was adopted to produce non-uniform electric fields\nwithin the insulation samples, potentially leading to electrical trees. The development of trees was\nmonitored through an optical method and the associated partial discharge signals were measured\nthrough an electrical detection technique, simultaneously. The analysis of the results shows reasonable\nrelation between the formation of ETs and the type of the applied voltages. The polarity reversing\nattribute of the test voltages has a pronounced effect on formation and growth of electrical trees.\nThis implicates an interaction between the space charges that accumulate within polymeric materials\nand the operational polarity reversing electric fields, which causes insulation degradation. Therefore,\nstudy of influencing HVDC operational parameters on insulation degradations can contribute to\nimprovements in cable design and advancement in insulation diagnostic strategies applicable in\nHVDC systems leading to more effective asset management.
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