A Novel Antioxidant Addition Strategy for Synthetic Ester Insulating Oils: Phenolic Compounding

The combination of phenolic and amine additives represents a traditional approach for the co-formulation of antioxidant compounds in insulating oils. However, the introduction of amines not only induces significant alterations in the inherent characteristics of the oil but also gives rise to aging by-products that are environmentally detrimental. This study examines the aging behavior of three commonly employed phenolic antioxidants, namely, butylated hydroxytoluene (BHT), butyl hydroxyanisole (BHA), and tert-butyl hydroquinone (TBHQ), when added individually or in combination with synthetic ester insulating oil. The investigation reveals that the co-formulation of phenolic antioxidants demonstrates exceptional antioxidant efficacy within synthetic ester insulating oil. Through the oxidative stability test, it is observed that incorporating a combination of 0.3 wt% BHT and 0.1 wt% BHA into the oil maintains the dielectric dissipation factor (DDF) at 0.681%, representing a mere 0.202% increase compared to fresh oil. Furthermore, the total acid number (TAN) can be sustained at 0.01 mg<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula>KOH/g, and the breakdown voltage (BDV) can be up to 78 kV. This study employs linear sweep voltammetry (LSV) and Fourier transform infrared (FT-IR) spectroscopy to analyze the behavior of antioxidants and the degradation products of aged oil samples. A preliminary investigation into the synergistic antioxidant mechanism of phenolic antioxidants in synthetic ester insulating oil is conducted, to provide a novel approach for the formulation of antioxidant compounds.