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 1 H, 13 C, 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 olefinic bond shift, the polymerization of soybean oil to generate the polymers with high molecular weight also contributed significantly to the soybean oil aging.

Multi-aging Effects on Vegetable Based Oils for Transformer Insulation in HV Systems

“…In terms of the aging process, the transformers are subjected to electrical and thermal stresses during operating conditions for their whole service life. Further, to simulate the lifecycle conditions in a shorter period, high voltage and temperature are applied to transformers, termed as accelerated aging equivalent to 31.8 years of practical service [21]. The fresh vegetable oil was initially filtered under vacuum conditions employing Whatman No.…”

“…AC voltage of 1 kV is applied to oil samples at 100 °C temperature during the aging process. The oil samples were under the aging process for seven weeks equivalent to 31.8 years in actual practice [20,21]. The oil samples were chemically examined and compared with transformer oil.…”