Identification of Impurities of Unknown Composition in Insulating Oil by Gas Chromatography-Mass Spectrometry (GC-MS)
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Vol. 54, No. 4, November, 2020
IDENTIFICATION OF IMPURITIES OF UNKNOWN COMPOSITION IN INSULATING OIL BY GAS CHROMATOGRAPHY-MASS SPECTROMETRY (GC-MS) M. N. Lyutikova,1 S. V. Nekhoroshev,2 V. M. Kuklina,3 and M. G. Kulkov3 Translated from Élektricheskie Stantsii, No. 6, June 2020, pp. 47 – 53.
This paper presents the results of a study of the behavior of an antioxidant additive (ionol) in insulating oil from existing high-voltage equipment. Decomposition products of the inhibitor (ionol), the concentration of which changes as the oil ages, were found in the oil samples. These compounds can be attributed to impurity compounds, which can also serve as additional markers of aging of a liquid dielectric. The ionol degradation products were analyzed by gas chromatography with a flame-ionization detector (FID) and a mass spectrometric detector (MSD). The advantages of the gas chromatography-mass spectrometric method over gas chromatography with an FID are shown. Compounds that are formed as the oxidation inhibitor (ionol) is consumed are identified using chromatography-mass spectrometry. It has been found that the ionol concentration decreases as the mineral oil ages. At the same time, the concentration of ionol “metabolites” increases and becomes much higher than the concentration of the additive itself. Keywords: antioxidant additive; ionol; insulating oil; insolation aging indicator; diagnostics of high-voltage equipment.
ionol concentration in mineral oil is strictly controlled in practically all types of high-voltage oil-filled electrical equipment, including metering current transformers, voltage transformers, high-voltage terminals, etc. Currently, several analytical methods are used in diagnostic laboratories for quantitative determination of additives [2]. Each method has its own advantages and disadvantages, e.g., gas chromatography (GC) with a flame-ionization detector (FID), which is most often used in Russian laboratories [3]. In particular, GC with an FID does not allow a chromatogram peak belonging to an unknown compound to be identified. This issue is highly interesting because many compounds that can indicate the degree of degradation of a liquid insulator form during its aging. The goal of the present work was to test a new method based on gas chromatography-mass spectrometry (GC-MS) to determine the antioxidant additive ionol and its degradation products. Figure 1 shows a diagram of the experimental setup.
The use of mineral oil as an insulating fluid and heat-exchange agent in high-voltage equipment began at the end of the 19th century [1]. Mineral oil has several advantages over gas or solid insulators, e.g., efficient heat removal from the active part and excellent soaking of kraft paper that is used, as a rule, as wrapping for wires and other items. Also, electrical power in liquid dielectrics is practically fully restored after a breakdown. Irreversible chemical changes can occur only after several repeated spark breakdowns (or with prolonged arcing). The ability to be oxidized by operating fact
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