Application of IR spectroscopy to control oxidation inhibitor (ionol) concentration in mineral transformer oils

Mineral insulating oils used as dielectric and heat dissipating agent in high voltage oil-filled equipment are subject to oxidation. Oxidation results in the appearance of undesirable substances that reduce the electrical insulating properties of liquids. Therefore, to inhibit the oxidation process, an antioxidant additive is introduced into transformer oils. In the overwhelming majority, 2,6-di-tert-butyl-4-methylphenol (ionol) is used as an inhibitor. Residual concentration of ionol is a regularly monitored parameter. In Russia, the main method for determining the concentration of ionol in oil is gas chromatography. However, fourier-transform infrared spectroscopy should be considered as an alternative method for monitoring the ionol content as it has a number of advantages over the gas chromatographic method. The paper compares the results of the determination of ionol in operational transformer oils using gas chromatography and the IR method. We justified that the method of IR spectroscopy has no limitations as applied to oils from power transformers equipped with adsorption purification systems.