Study on the Current Concentration and Local Heating of the Buffer Layer in HV XLPE Cables

In recent years, failures caused by ablation of water-blocking semi-conductive buffer layer in high voltage (HV) crosslinked polyethylene (XLPE) cables with corrugated aluminum sheaths have been frequently reported. In this paper, a two-dimensional axisymmetric model of 110 kV XLPE cable was established by finite element software, and the current field distribution was simulated. The results showed that the phenomenon of current concentration occurred at the close contact locations between the aluminum sheath and the buffer layer, and the peak current increased linearly with the noncontact length, which could lead to a significant local temperature rise. According to the numerical simulation, the temperature could rise 23.18 °C when the non-contact length is 1 m, while the temperature rise could reach 303.85 °C when the non-contact length is 4 m. In the experiment, the continuous application of the current caused the shrinkage of fibers and ablation spots appearing in the buffer layer in a dry condition, while under a wet condition, the insulation screen surface would become rough due to the appearance of circular white materials. It is proved, both numerically and experimentally, that the current concentration is one highly possible cause of the ablation phenomenon, and it is the reason why most of the buffer ablation occurs at the troughs of the aluminum sheath.