Analysis of influencing factors on buffer layer discharge for high-voltage XLPE cable

In the high-voltage (HV) cross-linked polyethylene (XLPE) cable, the buffer layer has the function of electrical connection and water-blocking. However, after water invades cables, the buffer layer discharge defect may occur, which can lead to the breakdown accident of cable line. It does serious harm to the safe and stable operation of the power system. At present, the buffer layer discharge defect has not been sufficiently investigated in existing research. This paper establishes a voltage distribution calculation model for analyzing the buffer layer discharge defect. The mechanism of how the presence of air gap and white marks (the corrosion products) between aluminium sheath and buffer layer influencing the voltage distribution inside cable is involved in this model. Based on the simulation software, a convenient method for solving the model is proposed. Using this model, the internal voltage distribution results of the cable under different forms of white marks are obtained. The influencing factors affecting the discharge of buffer layer are analyzed. The validity of the model is proved by the discharge test of the cable with controllable defects. The results show that the risk of buffer layer discharge can be quantitatively assessed by the white mark defect feature.