Life Assessment of XLPE Insulation for HVDC Cable Based on Thermo-oxidative Aging Kinetic Analysis with Improved Algorithm

High voltage direct current (HVDC) cables play a key role in long-distance power transmission and interconnection of grids. Cross-linked polyethylene (XLPE) has good mechanical and thermal properties and is more recent used for HVDC cable insulation. The thermal stress is one of critical aging actors for XLPE insulation. The thermal life estimated by quick methods based on thermogravimetric kinetic analysis is usually abnormal. In this study, the thermogravimetric analysis (TGA) of XLPE insulation is performed under air atmosphere and the thermogravimetric kinetic analysis is carried out for the first degradation stage reflecting the actual thermo-oxidative aging process. With the aid of nonlinear least squares fitting, two higher-accuracy temperature integral approximations are proposed. The approximation in exponential form is used to develop an improved method for solving activation energy regardless of reaction mechanism. The approximation in rational function form is used to establish a life equation because of its high accuracy. The activation energy calculation error of the improved method is proved to be much smaller than that of traditional Flynn-Wall-Ozawa (FWO) method and the estimated thermal life of XLPE insulation is experimentally verified to be reliable. This paper provides an effective life assessment method based on thermo-oxidative aging kinetic analysis for HVDC XLPE cable.