Application of Infrared Spectroscopy for Discrimination Between Electrical and Thermal Faults in Transformer Oil

Power transformer diagnostics and condition assessment are essential measures to increase the transformer's lifetime. In this regard, the dissolved gas analysis (DGA), the most common method worldwide in predicting the incipient faults in the transformer, is applied. Recently, the optical spectroscopy methods have attracted most of the attention towards effective monitoring of the state of power transformer insulation. Therefore, in this paper, Fourier Transform Infrared (FTIR) spectroscopy was employed to discriminate between the electrical and thermal faults that frequently happen in oil insulation. Regarding the electrical fault, it was simulated by applying repeated high voltage impulses to a fresh oil sample while the thermal fault was imitated through a localized overheating in another fresh oil sample with the help of a heating coil. Firstly, the two samples were examined via FTIR spectroscopy to obtain their FTIR spectra. Then, the effect of ageing on the spectrum was studied comprehensively for determining the degree of deterioration as well as any change that happen in the concentration or structure of the oil molecules. After that, both of them were analyzed by DGA to measure the concentration of the dissolved gases in the oil in order to confirm the FTIR spectroscopy results. In the final analysis, it was obvious that the implementation of the optical method is considered a promising tool to monitor the faulted oil and distinguish between the electrical fault and the thermal one making the FTIR spectroscopy a superior alternative for DGA.