Effect of DC testing water tree deteriorated cable and a preliminary evaluation of VLF as alternate

According to the experiences of some power utilities, the application of industry-recommended high storage DC field tests on 5-35 kV extruded dielectric cables containing water trees sometimes causes further deterioration of the insulation. Tests conducted on laboratory-aged 15 kV ethylene propylene rubber (EP) and 15 and 28 kV crosslinked polyethylene (XLPE) insulated cables indicate that DC proof tests in accordance with AEIC specifications and IEEE test guides without flashover do not appear to cause further deterioration. Depending on the degree of cable aging and the level of test voltage, when flashovers take place, damage may be inflicted on XLPE cables. No damage was observed on aged EP cable, at the same test levels.<
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