Molecular Mechanism Analysis of Multicomponent Mixed Insulating Oil Improving Lightning Impulse Discharge Characteristics of Oil-Impregnated Paper

During the operation of transformers, the oil-paper insulation system is susceptible to lightning impulse voltage. Investigating the lightning impulse discharge characteristics of a multicomponent mixed insulation oil-paper composite system can support the design of interturn and intercake insulation pad structures in transformers. This article examines the lightning impulse discharge characteristics of multicomponent mixed insulation oil-paper under extremely uneven electric fields. Using first principles and molecular dynamics theory, the study reveals the molecular mechanisms that enhance the impact resistance of oil-impregnated paper to strong electric fields from a microscopic perspective. The results indicate that, under pin-plate electrode conditions, the oil gap breaks down first. The positive and negative lightning impulse breakdown voltage of the multicomponent mixed insulation oil-paper is approximately 10%–40% higher than that of mineral oil-paper. Simulation results demonstrate that, compared to the mineral oil-impregnated paper, the multicomponent insulation oil reduces the dipole moment, self-diffusion coefficient, and radius of gyration of the oil-impregnated paper, while increasing the excitation energy, bandgap width, number of hydrogen bonds, lifetime of hydrogen bonds, intermolecular interaction energy, intramolecular interaction, and enthalpy of evaporation. These changes make the multicomponent insulation oil-paper system more resistant to electrical and thermal decomposition. This study provides a foundation for the safe and reliable operation of multicomponent mixed insulating oils in high voltage and large capacity transformers.