Correlation between Terahertz Spectrum and Insulating Oil Quality

The quality of insulating oil is a decisive factor for the safe operation of oil-filled high-voltage equipment. Acid, moisture, furfural, and other polar products and impurities produced by the deterioration of oil-paper insulation are important reasons for the decline in oil quality such as increased dielectric loss and decreased breakdown strength. Terahertz wave has a sensitive response to polar substances and strong penetration to weak polar substances. It is expected to realize the detection of trace polar products in weak polar insulating oil with a high signal-to-noise ratio. In this paper, the relationship between terahertz spectral characteristics and dielectric loss, acid value, and furfural content of insulating oil is studied. The results show that there is a good positive correlation between the characteristic peak area of the terahertz absorption spectrum around 1 THz and the dielectric loss of insulating oil. According to the simulation calculation, it is found that acetic acid and furfural have polar molecular characteristic peaks at 2.1 THz and 3.8 THz. And there is a good positive correlation between the peak height of the test sample at these two bands and the acid value and furfural. In the future, the number of samples can be further expanded, a mathematical model of terahertz characteristics and insulating oil quality can be established, and the accuracy and universality of the model can be verified.