Effect of Molecular Microscopic Parameters of Silicon Rubber on Trap Formation and Surface Discharge Under External Electric Field

The surface discharge under strong electric field is mainly caused by electrons, which is closely related to traps in solid medium. In this paper, the effects of the structure, the frontier orbital energy level, and the excited state of methyl vinyl silicone rubber (MVQ) on the formation of the trap and the surface discharge were investigated at the atomic and molecular level by using the density functional theory. The results show that the lowest unoccupied orbital and atomic charge population of MVQ molecule reflect that the vinyl region in the molecule gradually evolves into electron traps, and the trap gradually deepens with the increase of electric field. The electrophilic activity of the vinyl region activates the trapped electrons in the trap. During the surface discharge process, the electrons accumulated in this region will promote the development of electron avalanches due to their strong activity. The excitation energy of the MVQ molecular decreases, which makes the electrons within the molecule easy to be inspired. The vinyl area is the main excitation area, where the electrons will emit photons in the process of back excitation after excitation, which can facilitate the spatial photoionization of the surface gas molecules. The bond levels of some Si-O bonds and C-H bonds in molecules gradually decrease with the increase of external electric field. The molecules are prone to break bonds and generate free radicals, which are easily converted into plasma by free electrons produced after ionization with gas molecules, thus leading to the occurrence of electron avalanches. © 2022, High Voltage Engineering Editorial Department of CEPRI. All right reserved.