Oxidative Stability of Soybean Oil under Accelerated Transformer Conditions: Comprehensive Mechanistic Studies

Abstract

Understanding the oxidative mechanism of the natural ester based insulating oils will benefit the seeking of the antioxidants for their long time service in a transformer. The present studies introduced a comprehensive investigation on the oxidative mechanism of soybean oil under accelerated aging conditions through 1H, 13C, DEPT-135 NMR, GPC, ICP, viscosity analysis, and chemical scavenger tests. It was found that superoxide radical, generated by copper wire activated oxygen, played a significant role in soybean oil aging. Capturing the superoxide radical by benzoquinone almost completely inhibited the oxidation of soybean oil under the accelerated aging conditions as well as adding the well-known 2,6-dibutyl-4-methylphenol as additives. The dissolved copper(II) cation, generated in the aging process, also accelerated the oxidation due to its hydrogen abstraction ability to soybean oil. In addition to the common oxidation through the well-known free radical chain process and isomerization through olefini...