Comparison of Phenolic Antioxidants’ Impact on Thermal Oxidation Stability of Pentaerythritol Ester Insulating Oil

Synthetic ester insulating oil emerges as an environmentally friendly substitute for mineral insulating oil. However, the intrinsic ester structure poses challenges to its oxidation stability, making improvement necessary. This article compares the impact of three phenolic antioxidants, specifically 2,6-di-tert-butyl-4-methylphenol (T501), tert-butylhydroquinone (TBHQ), and 4,4’-methylenebis (2,6-di-tert-butylphenol) (T511), on improving the thermal oxidation stability of pentaerythritol ester insulating oil (KKA). The antioxidants are introduced at molar ratios of 6 and $18~\mu $ mol/g. The thermal oxygen aging tests indicate that all three antioxidants mitigate the deterioration of KKA’s physicochemical and electrical properties to varying extents. TBHQ exhibits the most pronounced effect on enhancing KKA’s thermal stability, as evidenced by the highest extrapolated onset temperature obtained via thermogravimetric analysis and differential scanning calorimetry (TG-DSC) in a nitrogen atmosphere. T511 is the most influential in improving KKA’s oxidation stability, characterized by its superior onset oxidation temperature and highest capacity to elevate the initial oxidative activation energy of KKA determined through nonisothermal DSC. Furthermore, the lowest bond dissociation energy (BDE) ofT511 indicates a most facilitated release of hydrogen atoms, providing additional evidence for its superior antioxidant efficiency.