Abstract
Analyzing the concentration of low molecular acids dissolved in oil is vital in the oil-paper insulation aging diagnostic procedure of power transformers. The existing methods cannot distinguish between different acid types and their strengths. In this study, an improved solution Raman detection platform is fabricated. The direct measurement of dissolved acetic acid, a kind of low molecular acids, is observed in transformer oil without extraction. The Raman shift line of oil-dissolved acetic acid at 891 cm−1 corresponding to H–C–H symmetrical swing and O–H swing modes is taken as its characteristic value. Taking Raman shift line of pure oil at 932 cm−1 as an internal standard, a linear regression curve for quantitative analysis is obtained with a slope of 0.19. The best platform parameter of accumulation number is 300, which is determined by Allan deviation analysis. The current concentration detection limit and accuracy for oil-dissolved acetic acid are obtained at about 0.68 mg/mL and 91.66%, separately. The results show that Raman spectroscopy could be a useful alternative method for evaluation insulation aging state of an operating power transformer in the future.
Highlights
IntroductionOil-immersed transformers are one of the most important electrical components in power systems
Oil-immersed transformers are one of the most important electrical components in power systems.Their reliability is significant for the safety and stability of power grids [1]
Improvements made on our previously introduced solution Raman detection platform is reported for getting higher detection limit, including using a quartz cuvette and two edge filters
Summary
Oil-immersed transformers are one of the most important electrical components in power systems. Their reliability is significant for the safety and stability of power grids [1]. High-molecular-weight acids (more than 5 carbon atoms), typically stearic and naphtenic acid, have a lower affinity for cellulose due to the hydrophobic nature of the alkyl group Cn H2n+1 [10,11], while, low-molecular-weight acids, typically formic, levulinic, and acetic acid, are more hydrophilic and 90% of which will be absorbed by the oil-immersed paper [12]. It has been demonstrated that a precise analysis of the concentration of low molecular acids along with content of water in oil and in paper is of great value for assessing ageing condition and for assessing the effect of maintenance actions [16,17]
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