Multi-dimensional Analysis and Correlation Mechanism of Thermal Degradation Characteristics of XLPE Insulation for Extra High Voltage Submarine Cable

This paper focuses on the multi-dimensional performance analysis including the oxidation performance, crystal morphology, thermal properties, mechanical properties and dielectric behavior of the thermally aged extra high voltage XLPE submarine cable insulation. Results show that the antioxidation and thermal oxidative aging of XLPE insulation are coexisting and competing during the thermal degradation process. In the early stage of thermal degradation, the antioxidation of XLPE insulation is dominant resulting in the decline of the spacing between spherulites. In the later stage of thermal degradation, thermally oxidative aging of XLPE insulation is dominant, which leads to the damage of the crystalline morphology and the rapid generation of aging products. It is indicated that the mechanical strength of the XLPE insulation is mainly determined by its internal crystalline morphology, while the dielectric properties of the XLPE insulation are governed by the crystalline morphology, aging products and micro interface. With the thermal aging time extended, the breakdown strength of XLPE insulation first increases and then decreases, which is determined by its amorphous region and aging products.