Water Tree Degradation Impacting on the Insulation Performance of Highly-aged MV/HV-class XLPE Cable

MV/HV-class XLPE cables are vital in underground power networks in Japan, installed in underground pipes where groundwater infiltration creates humidity. For wet-design cables having no water barrier (e.g., metallic sheath or glued metallic foil), moisture can penetrate the sheath and insulation, forming water trees, bow-tie trees (BTTs) and vented trees (VTs), bringing about decrease in electrical insulation performance. Prior works only investigated the wate trees in the insulation of the cable specimen near breakdown point.