Analysis of Free Energy Increment for Insulation Aging in Crosslinked Polyethylene DC Cable

Electrical aging limits the reliability of crosslinked polyethylene DC cable. The study on the reaction kinetics of electrical aging is an important basis of improving the reliability of DC cable. Free energy increment (FEI) under electric field reflects the reaction rate of electrical aging, which is very useful to analyze the aging characteristics of materials. However, there is no direct way to get the FEI, which causes that the FEI stays at the stage of theoretical analysis and cannot be obtained by experiment. In this paper, an easy method including experiment and calculation to get the FEI is proposed, and a simulation method to obtain the FEI is also introduced. The experiment and simulation both show that the FEI of crosslinked polyethylene (XLPE) is proportional to the degree of polymerization, is approximately linear with the electric field, and grows with the temperature. According to the FEI obtained, we find that the molecular branches of the XLPE whose plane of carbons is perpendicular to electric field are more likely to age. Improving molecular chain orientation and reducing the length of branches are two of the methods to improve the aging characteristics of the XLPE.