Final breakdown in field-aged XLPE

Water tree growth in field-aged cross-linked polyethylene (XLPE) was investigated. The tests were performed on 600- mu m-thick ribbons peeled off from a field-aged 28-kV cable. Water tree growth in the samples saturated at around 70% of sample thickness after 12000 hours of aging, probably due to ion consumption. Ion concentration of the electrolyte solution influenced water tree growth. No correlation was found between the sample location in the insulation and water tree length. AC breakdown strength decreased with aging time and ion concentration. Under the present conditions water trees behave as dielectrics. No electrical tree was observed even with water needle samples.<
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