Experiment and Simulation of Leakage Current in HVDC Cable under Different Electro-Thermal Stresses

In the recent decades, HVDC XLPE cables have been in use for long distance transmission of power. A good insulator must have very low conductivity, low losses and high thermal stability. It is believed that, impurities, multiple voids, moisture and other contamination in the insulation may lead to increase in leakage current which causes losses in insulation, eventually leading to degradation or failure of insulation. Under high electric and thermal stresses, during transients such as switching, high load and sudden change in loads may lead to a faster rate of degradation of the insulation. So, it’s important to measure insulation leakage current to identify the status of insulation. In this paper, the authors have experimentally measured the leakage current of an actual XLPE cable under different electro-thermal stresses. The leakage current has also been simulated under similar stresses using interdependent distributed electrical and thermal circuit models. The nonlinearly varying DC conductivity of the insulation, characterized experimentally, has been incorporated in the simulation. The multi-factor dependency has been implemented in the circuit simulation. Using simulation model, the leakage current can be estimated for varying electric and thermal fields.