# Quantifying the Effect of Catalysts on the Lifetime of Transformer Oil  
[PERSON]  
1 Faculty of Electrical Engineering, Regional Innovation Centre for Electrical Engineering, University of West Bohemia, Univerzitn 8, 306 14 Pilsen, Czech Republic; [EMAIL_ADDRESS] (P.H.J.); [EMAIL_ADDRESS] (P.K.); [EMAIL_ADDRESS] (D.M.); [EMAIL_ADDRESS] (P.P.)  
1 Faculty of Electrical Engineering, Regional Innovation Centre for Electrical Engineering, University of West Bohemia, Univerzitn 8, 306 14 Pilsen, Czech Republic; [EMAIL_ADDRESS] (P.H.J.); [EMAIL_ADDRESS] (P.K.); [EMAIL_ADDRESS] (D.M.); [EMAIL_ADDRESS] (P.P.)  
1 Faculty of Electrical Engineering, Regional Innovation Centre for Electrical Engineering, University of West Bohemia, Univerzitn 8, 306 14 Pilsen, Czech Republic; paulm1@ket.  
oxygen is suppressed; therefore, the temperature remains a dominant factor influencing the lifetime of the transformer insulation [6]. A convenient way to slow down the thermal oxidation of the used mineral oil, and thus to prevent the fast degradation of the whole transformer insulating system, is the addition of an appropriate antioxidant. A phenolic antioxidant, such as 2,6-di-tert-butyl-4-methylphenol (CAS no. 128-37-0), also called 2,6-di-tert-butyl-p-cresol (DBPC), is usually used for such purposes [7; 8].  
Nevertheless, the properties of mineral oil do not deteriorate solely under the influence of the abovementioned temperature, but also because of the presence of metallic particles originating mainly from copper winding wrapped in the insulating paper and immersed in the transformer oil. Metallic particles, together with moisture, which is naturally present in the structure of cellulose paper, can synergistically act as catalysts [9; 10], accelerate oil-paper insulation aging, and hence, reduce the lifetime of the whole transformer. For these reasons, the influence of catalysts on the aging mechanisms of transformer insulation has attracted the attention of numerous researchers in recent years, leading to studies by [PERSON] [11] and [PERSON] [12], technical brochure CIGRE WG A2-32 [13], and others. The majority of these studies have addressed the role of copper sulfide formation and its influence on transformer failure. With a few exceptions, e.g., a recent study by [PERSON] et al. [14], insufficient data exist to enable the exact quantification of the synergic effect of catalysts on the lifetime of transformer mineral oil. [PERSON] et al. [14] addressed the catalytic effect of copper on the thermal aging rate and the micro/nanolevel morphology of the oil-paper insulation aged with and without copper at 130 \({}^{\circ}\)C for 80 days (1920 h). These researchers confirmed that copper plays a catalytic role in the aging of naphthenic oil-paper insulation, and that this role becomes obvious during the later stages of the aging process. The thermal aging rate of paper was higher for the oil-paper insulation aged with copper. Nevertheless, considering that all of the aforementioned findings, that most likely depend on the temperature of aging, it is necessary to extend the research activities in this field and attempt to quantify the effect of catalysts on the lifetime of transformer oil at various aging temperatures. Such an experiment would provide further insight into the dynamics of mineral oil aging in the presence and absence of catalysts.  
For these reasons, within this study, the tested mineral oil was exposed to accelerated thermo-oxidative aging at temperatures of 110, 120, and 130 \({}^{\circ}\)C for times ranging from 24 to 2424 h in the presence and absence of catalysts. The effect of catalysts on the lifetime of transformer oil was then quantified using ultraviolet-visible (UV-Vis) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy.