Effect of Thermal Ageing on Insulation Properties of 500 kV DC XLPE Submarine Cable Insulation

Thermal ageing of cross-linked polyethylene (XLPE) insulation cable is considered as a critical factor and can change the insulation properties distinctly. This paper presents the influence of thermal ageing on the insulation properties of 500 kV DC XLPE submarine cable insulation. The cable insulation is cut into three layers (inner layer, middle layer and outer layer) in a cylindrical shape. The thermal aging is carried out at 106°C for 250, 500, 750 and 1000 hours, respectively. The electrical and materials properties are analyzed. The result shows that the evident hetero charges are accumulated inside the unaged middle layer. The thermal aging can reduce the local space charge accumulation and the electric field distortion rate, whereas it decreases the DC conductivity of the samples. Diffraction peak intensity of (110) and (200) crystal are affected due to the thermal ageing. The transmittance peak of the C-O-C symmetric stretching vibration peak is observed. It is found that the thermal ageing of a short time is helpful to improve the physical and chemical properties of the samples. The material analysis shows that the oxidation process is suppressed by the antioxidant.