Ablation Mechanism of Water-blocking Buffer Layer in HV XLPE Cables

In recent years, ablation failures of the water-blocking buffer layer in HV XLPE cables occur frequently, which has attracted widespread attention in the industry. In order to study the ablation mechanism of the water-blocking buffer layer, a simplified test platform was set up and comparative experiments were carried out corresponding to the actual operating conditions of the cable. Besides, a finite element simulation model was established for a 110 kV cable, with the dielectric parameters of the buffer layer assigned according to the measured data. Finally, the electric potential and field distribution were analyzed when the corrugated aluminum sheath and the buffer layer were contacted in different forms. The results show that, with the buffer layer getting damp, its resistivity and permittivity both increase, and the white substance appears under the applied current. The white substance containes water blocking powder and aluminum oxide products, and its non-conductivity will lead to the poor electric contact between the aluminum sheath and the insulation screen. When the axial length of the poor contact between the water-blocking buffer layer and the corrugated aluminum sheath reaches 0.4 m, the field strength in an air gap with a height of 0.1 mm will exceed 3 kV/mm, which can trigger the discharge. Damp of the buffer layer is the main reason of ablation failures, and the gap between the buffer layer and the aluminum sheath also affects the occurrence of air gap discharge. Therefore, it is suggested that the damp of the buffer layer should be avoided in the manufacturing and construction stages of HV cables, and the effective and continuous electrical contact between the buffer layer and the aluminum sheath should be strictly guaranteed. © 2021, High Voltage Engineering Editorial Department of CEPRI. All right reserved.