Modeling water tree phenomenon for insulated cable loss current estimation

Water tree degradation phenomenon constitutes a serious problem in XLPE insulated power cables. The presence of water trees lead to harmonic components in the insulation loss current, of which analysis provides a powerful indication of the state of the degradation. The first goal of this study is to establish a procedure to recover the measured loss current waveform in XLPE cables with water tree degradation by numerical calculations, and the second is to identify the loss current component from the total current that flows in the insulation. A new methodology based on the measured loss current waveform and the parameters calculations of the suggested equivalent circuit for the insulation with water trees is presented. It allows getting the THD of the loss current, the dissipation factor (tan delta) and the power losses in the insulation (p). It is also possible to determine its equivalent capacitance (C) and equivalent resistance (R). It is shown that the proposed methodology reproduces with a very good accuracy the loss current waveforms obtained in experiments.