Assessment of thermally aged XLPE insulation material under extreme operating temperatures

Abstract

The degradation of cross-linked polyethylene (XLPE) insulation material is critical for the safe operation of cables. While there are extensive studies on the thermo-oxidative ageing of XLPE at or below 130 °C, the maximum overload conductor operating temperature, the short circuit temperature can rise above 150 °C, and the ageing patterns at these situations have not been fully understood. Here, chemical, crystalline structure, cross-linking density as well as the mechanical properties were characterized. The results demonstrate the importance of antioxidants in the high temperature situation. Before antioxidants are completely consumed, most of the mechanical and physicochemical properties remain stable. While antioxidant is depleted, the thermo-oxidative degradation is detrimental to the structure and properties of the insulation. The activation energy is around 160 kJ/mol for the thermo-oxidative ageing, from which the lifetime allowed before serious destruction of the insulation at different shortage or overload temperatures can be calculated.