Investigating the Impact of Phenolic Antioxidants on the Oxidation Stability of Synthetic Ester Insulating Oil

As an environment-friendly ester-based insulating oil, synthetic ester possesses the advantages of strong biodegradability, good biocompatibility, a high flash point and fire point, and great chemical stability. However, the inherent ester structure in synthetic ester molecules is one of the risks that threaten its oxidation stability. Therefore, in this paper, the focus is on the influence of three phenolic antioxidants on the oxidation stability of synthetic ester insulating oil, specifically 2,6-di-tert-butylphenol (BHT), tert-butylhydroquinone (TBHQ), and 4,4'-methylenebis (2,6-di-tert-butylphenol) (T511). To assess the antioxidant effectiveness of oil samples, the oxidation onset temperature is evaluated using differential scanning calorimetry (DSC). Meanwhile, the physicochemical and dielectric properties of synthetic ester insulating oils containing phenolic antioxidants are also investigated to determine whether the performance of oil samples complies with the insulation requirements. The results demonstrate that although antioxidant application may slightly reduce the insulation properties, the three antioxidants all play a significant role in enhancing the oxidation stability of synthetic ester insulating oil. When added in the same molar ratio, T511 exhibits the strongest oxidation resistance, followed by TBHQ.