The Hidden Vulnerabilities of Pentaerythritol Synthetic Ester Insulating Oil for Eco-Friendly Transformers: A Dive Into Molecular Behavior

Ester-based insulating oils exhibit high flash points and biodegradability. Their inferior lightning impulse breakdown voltage (LIBDV), however, hinders the development of high-voltage, large-capacity, eco-friendly transformers. This study compares the negative LIBDV of 25#mineral oil (25#MO) and self-developed pentaerythritol synthetic ester oil (SEO-KA). Subsequently, employing density functional, time-dependent density functional, and wave function analysis methods, calculations are conducted to propose the influence mechanisms of frontier orbitals and traps, ionization and electron affinity processes, excitation processes, discharge active sites, and molecular polarity on LIBDV for both oils. The results indicate that the negative LIBDV of 25#MO is over 1.4 times that of SEO-KA under tested oil gaps. SEO-KA exhibits greater inherent dipole moment, induced dipole moment, and molecular polarity than 25#MO. The frontier orbitals are easily movable, and the trap energy level distribution is denser. The uneven distribution of surface electrostatic potential triggers more discharge active sites. Fortunately, SEO-KA can maintain negative electron affinity and local excitation types, demonstrating similar electronic reactivity and molecular stability to 25#MO. Future work can focus on improving the ionization energy of SEO-KA to enhance its LIBDV. This research provides a scientific basis and guidance for the design, development, and application of superior-performance eco-friendly insulating liquids.