Macroscopic behavior and microscopic mechanism analysis of lightning impulse breakdown properties of three-element mixed insulation oil under long oil gap

The study of the lightning impulse breakdown (LIB) characteristics in three-element mixed insulation oil (TEMO) is crucial for the design of high-voltage large-scale transformers utilizing TEMO. Consequently, the LIB of TEMO under long oil gaps and negative polarity was carry out, with mineral oil (MO) serving as the reference for comparative analysis. The focus is on parameters such as average breakdown voltage, average discharge development speed, and particle size content in the oil after breakdown. The LIB voltage of the TEMO was examined by using the Weibull distribution. Additionally, through first-principles and molecular dynamics simulation, the microscopic changes and differences in parameters of TEMO and MO under varying electric field were anlaysed. The research results reveal that the average LIB voltage of TEMO, along with the breakdown voltage at various failure probabilities, is lower than that of MO for any specified gap. However, as the oil gap length increases, the difference in LIB voltage between TEMO and MO becomes less pronounced. Simulations suggest that TEMO’s lower ionization potential, excitation energy, and forbidden band width in comparison to MO are the key factors causing the differences in LIB characteristics between the two oils.