Quantitative Analysis of Dissolved Gases in Transformer Oil Based on Multi-Parameter
CHEN Xin-gang1, 2, FENG Yu-xuan1*, LI Chang-xin1, CHEN Shu-ting1, CHEN Xiao-qing1, LONG Yao1, CHEN Lin-chi3
1. Chongqing University of Technology, Chongqing 400054, China
2. Chongqing Energy Internet Engineering Technology Research Center, Chongqing 400054, China
3. Chongqing University of Post and Telecommunications, Chongqing 400065，China
Abstract：The rapid and accurate detection of characteristic gases（H2，CO，CO2，CH4，C2H4，C2H6，C2H2） in oil is an important part of transformer on-line monitoring. Laser Raman spectroscopy is suitable for the detection of characteristic gases and can overcome many shortcomings of traditional on-line monitoring. When the characteristic gas in transformer oil is detected, the characteristic peaks of methane (CH4) and ethane (C2H6) gather in the Raman spectrum from 2 900 to 3 300 cm-1. It is of great significance to study the mixed gases samples with different content ratios in this spectrum for the quantitative analysis of mixed gases in transformer oil. Based on the research of Raman spectroscopy detection of single characteristic gas, the spectral peak height, full-width at half-maximum and spectral peak area parameters of the characteristic peaks in the pretreated spectrum are selected as the characteristic factors to quantitatively analyze the mixed gas in the transformer oil. According to the second-order perturbation theory, there are four characteristic peaks in the methane Raman spectrum, and the selected spectrum contains two peaks with 3 111 and 3 284 cm-1 as the Raman shift center. Six characteristic peaks exist in the Raman spectra of ethane, and there are two peaks of 3 111 and 3 187 cm-1 in the selected spectral bands. In theory, the amount of both gases can be calculated by the information of the characteristic peak carried in the spectrum bands. Through the detection of Raman spectroscopy platform, the characteristic peaks of the mixed gas spectrum will produce translation and polymerization. In practice, four peaks with shifts center of 1 902, 2 918, 2 956 and 3 022 cm-1 were found in the spectrum. A Gaussian function model was established for the four mixed peaks, and the spectral peak height, full-width at half-maximum and spectral peak area of the characteristic peak was obtained. A partial least squares regression model (PLS) was established. The spectral peak height, full-width at half-maximum and spectral peak area were taken as independent variables, and the two gas contents were taken as dependent variables for calculation and analysis. When the potential factor of the model is taken to t6, the adjusted R-square is 0.993, indicating that the independent variable has a definite relationship with the dependent variable, and the regression model is reliable. The analysis of regression equation parameters shows that the full-width at half-maximum of spectral peaks contribute significantly to the area and height of spectral peaks, which is in line with the expected target. Four characteristic spectral peaks in the spectrum of mixed gases have an effect on both gases. It can be concluded from the experiments that for the methane-ethane mixed gas, at room temperature 25 ℃, integration time 15 s, integral number 2, slit 100 μm, by obtaining the peak height, peak area and full-width at half-maximum three parameters, the gas content can be accurately measured, which lays a foundation for the simultaneous detection of various characteristic gases in transformer oil.
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