New near-infrared absorbance peak for inhibitor content detection in transformer insulating oil

Monitoring the condition of transformer insulating oil has been considered as a crucial and effective measure for preventive maintenance of power transformers. Various properties of the oil can be monitored such as the dissolved gases, furan content, and inhibitor content. This paper focuses on the inhibitor content in insulating oil. Currently, Fourier transform infrared (FTIR) spectroscopy in accordance with the IEC 60666 standard is used for the measurement of inhibitor concentration in insulating oil. However, this technique involves site sampling, transportation to a laboratory and an expensive instrument. This work proposes the characterization of inhibitor content in insulating oil in the near-infrared (NIR) waveband, which would lead to the design of a faster and cheaper detection system for inhibitor content. It was found that the inhibitor content exhibits an optical absorbance peak at 1403 nm, which was not reported in any previous work. A mathematical model was then created to describe the relationship between the concentration of inhibitor, the area under the absorbance spectrum and the peak optical absorbance. The model was verified, and the results showed a root mean square error (RMSE) of 0.0458.