Condition assessment of XLPE insulated cables based on polarization/depolarization current method

The water tree is one of the key factors leading to the insulation property deterioration in cross-linked polyethylene (XLPE) cables. An accelerated ageing experiment has been performed to produce water trees with the purpose of ageing the full-size XLPE cable under the high-frequency electric field. Based on Polarization and Depolarization Current (PDC) method, the diagnostic tests are employed to evaluate the ageing extent of the cable subjected to water tree at different ageing time. Results show that the average length of water trees is proportional to the ageing time, and thus the experiment is effective to accelerate the growth of water trees. Furthermore, such various diagnostic indicators as the I∗t∼lnt curves, the loss factor at different frequency, have their rules to assess the ageing condition of the cable with the duration of ageing time. Therefore, information obtained from PDC current can be used for determining the ageing extent of the cables.