Detection of Methanol in Power Transformer Oil Using Spectroscopy

Oil-paper insulation in transformers plays an important role in the operation of power grid. At present, the aging (life assessment) of transformers are mainly conducted based upon the degree of polymerization, concentration of furfural, and the gas analysis of CO and CO 2 in the transformer oil. However, these techniques lack sensitive response, especially in the early aging of oil-paper insulation. Methanol as a new indicator to evaluate the aging of insulating paper, is getting more and more attention. An evaluation method based on the measurement of methanol concentration using ultraviolet–visible spectrometer was proposed in this work. After the extraction from transformer oils, the methanol was oxidized using potassium permanganate. Then, chromotropic acid was used to react with the oxidation products (formaldehyde) to form a mauve clathrate, finally, the methanol content was measured using the spectroscopy. Different from traditional spectroscopy which calculate only by absorbance at the characteristic wavelength, this paper use the partial least squares method, obtain the relationship between the absorbance at selected regions and the concentration of methanol. The minimum detection limit for the proposed method was 10 ppb, whereas the correlation coefficient for the relationship between the absorbance and the concentration of methanol was as high as 0.99.