Differential Analysis of Electronic Structural Parameters Between Mineral and Synthetic Ester Insulating Oils

Insulating oil is a crucial dielectric fluid widely employed in oil-immersed transformers. Synthetic ester oil (SEO), characterized by its balanced performance, renewability, and biodegradability, is gradually replacing traditional mineral oil (MO). However, SEO is prone to rapid streamer discharge under lightning impulse voltage, leading to a breakdown voltage lower than that of MO. To comprehend this phenomenon, density functional theory and time-dependent density functional theory are employed to calculate and summarize the electronic structural parameter variations and correlations with macroscopic discharge behaviors of SEO and MO molecular under different electric fields. The results indicate that the inherent and induced dipole moments of SEO are greater than those of MO, making it more prone to forming space electric field. The energy gaps of MO and SEO consistently remain above 10 eV and 8 eV, respectively, suggesting their ability to maintain high resistivity under intense electric fields. The faster decrease in ionization potential of SEO triggers electron impact ionization, and the consistently negative electron affinity indicates that SEO is less prone to forming negative ions. The excitation energy of SEO is slightly smaller than that of MO, and both could maintain relatively stable excitation energy under intense electric fields, making them less susceptible to photoionization.