Life assessment of TUK and Nomex-910 impregnated mineral transformer oils using Raman spectroscopy

Concentration of furfural (Furan-2-carbaldehyde) in transformer oils is a well-known indicator for thermal degradation in oil-paper insulation. The application of Raman spectroscopy to determine thermal deterioration as a function of Furfural concentration can overcome many disadvantages of traditional detection methods and accelerated testing. In the present paper, thermal stability of thermally upgraded Kraft (TUK) and Nomex-910 impregnated mineral transformer oils has been investigated at higher accelerated thermal stresses. Samples having a standard mass ratio of oil and paper insulations in accordance with IEEE Std. C57.154-2012 have been studied. These samples were thermally stressed at 120°C and 150°C. Subsequently, the aged samples were analyzed using Raman spectroscopy test. Furfural was characterized by Raman signal at 1705.69 cm
^-1
, where no spectral interferences caused by oil-derived Raman signals occur. It has been observed from the test results that the oil sample consisting of TUK has higher life than that of the Nomex-910 immersed oil sample. It indicates that the Furfural formation in TUK test samples is more as compared to its Nomex-910 counterpart. Hence the degradation rate of TUK oil samples is more at higher temperatures. Consequently, Nomex-910 has been found more suitable for high temperature applications than TUK.