Effect of Moisture on the Breakdown Performance of XLPE Insulation: A First-Principles Study

Abstract

Traditionally, the research on the breakdown performance of XLPE mostly adopts experimental methods. This article attempts to study the influence of moisture on the breakdown performance of XLPE and the mechanism of action based on first principles and calculation methods. The Monte Carlo method was used to build a pure XLPE amorphous region unit cell model and simulate the damp condition of XLPE by adding water molecules. The geometry optimization and single point energy and band structure calculation were performed for above models by using the plane wave pseudopotential method. Some parameters, including the maximum displacement, maximum stress, total ground state energy, band gap and bond length, were calculated to study the effect of moisture on the breakdown performance of XLPE insulation. The calculation and analysis results show that for the cross-linked polyethylene model without moisture, as the external electric field intensity increases, the total energy gradually decreases, the band gap will be narrower, and the chemical bond length at the cross-linking position becomes larger. While the electric field intensity reaching a certain level, some C-H bonds and C-C bonds will be separated. It is shown that the molecular structure of XLPE was destroyed under strong electric field, and the breakdown performance of XLPE material deteriorated. Compared with the above model, for crosslinked polyethylene model containing water, the ground state energy decreased significantly, band gap was narrower, indicating that the existence of water molecule can reduce XLPE breakdown strength. The total energy and band gap show the declining trend and chemical crosslinking position bond length is larger as well with the increase of electric field intensity.