Results of an experimental investigation into the effect of insulation temperature rise on the leakage current in crosslinked polyethylene (XLPE) insulated underwater power cables under alternating (50 Hz) and direct voltage stresses are presented. The effect of the surrounding water contamination and the size of XLPE cable as well as the applied voltage on leakage current are investigated. The results are compared with experimental results on impregnated-paper submarine cables of the same ratings. (1) Insulation capacitive impedance is the dominant factor affecting leakage current under AC voltage stress, while insulation resistance is the main impedance limiting leakage current under DC voltage. (2) The leakage current increases with applied AC and DC voltage. (3) Nonlinearity of leakage current vs. applied DC voltage can be caused by corona discharge currents. (4) The leakage current in XLPE cables increases with decreasing water resistivity and becomes higher than that of impregnated-paper submarine cables for water salt-content near that of natural seawater. (5) Insulation temperature has a great effect on the leakage current of XLPE cables, whereas leakage current of impregnated-power submarine cables does not change significantly with temperature due to their better thermal conductivity.
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