State Detection Of Transformer Insulating Oil And Paper Based On Terahertz Spectrum

Terahertz(THz,1THz=10¹²Hz)wave refers to the electromagnetic wave whose frequency is in the range of 0.1-10 THz.It contains quite rich physical and chemical properties,and also has the advantages of low energy and non-destructive testing.In recent years,it has become a research hotspot in various industries.Under the background of vigorously building UHV network and smart grid,higher requirements are put forward for the insulation performance of oil immersed power equipment.Therefore,its operation state needs to be paid more attention to in order to eliminate potential safety hazards and reduce the accident rate.In this paper,terahertz time-domain spectroscopy technology is introduced into the aging state monitoring of transformer insulating oil paper.First,the insulating oil paper is aged at 130℃by accelerated thermal aging technology to obtain the experimental samples;then,the original spectral signal is obtained by using the self-made PE container,after the insulating oil sample is filled,the terahertz spectrum test is carried out to obtain the original spectral signal,and then the signal is processed by using the improved electromagnetic wave transfer function to obtain the terahertz optical parameters of the insulating oil;finally,the quantum theory is used to obtain the terahertz optical parameters of the insulating oil chemical software is used to simulate the frequency vibration of cellulose insulating paper and identify the fingerprint absorption peak.The main conclusions are as follows:（1）Due to the existence of Fabry-Perot effect（F-P）,there are many secondary peaks in the experimental data,which leads to echo oscillation in the frequency spectrum.The improved electromagnetic wave transfer function can be used to filter the echo oscillation without reducing the frequency resolution,and then more accurate sample data can be obtained.（2）Through the analysis of sample data,it is found that mineral insulating oil has two characteristic absorption peaks at 1.14 and 1.40 THz,and FR3 vegetable insulating oil has two absorption peaks at 1.30 and 1.50 THz.The average refractive index of mineral insulating oil and FR3 vegetable insulating oil in the range of 0.1-1.80 THz is1.459 and 1.533.At the same time,the dielectric properties of the two insulating oils in the range of 0.1-1.80 THz are studied,and obvious relaxation behavior can be observed in the dielectric loss spectrum.Through the analysis of furfural concentration in oil,it is found that there is a good correlation between THz parameter and furfural concentration.（3）Using 6-311+G（D,P）group in Gaussian software and B3LYP method in DFT,the quantum chemical calculation of frequency vibration of cellulose insulating paper monomer was carried out,and the absorption peak was assigned.The results show that there are obvious absorption peaks at 0.18,0.82,1.47 and 1.53 THz in theoretical calculation,while there are obvious absorption peaks at 0.17,0.49,0.82,1.20,1.42,1.53 and 1.74 THz in experimental test.It is found that the absorption peak in the theoretical calculation is caused by the different vibration forms of the intramolecular chemical bond.The absorption peak in the experimental test includes not only the intramolecular vibration,but also the intermolecular vibration.（4）Through the analysis of THz optical parameters of cellulose insulating paper with different thermal aging degree,it is found that the average refractive index of unaged cellulose insulating paper in the range of 0.1-1.80 THz is 1.531,which changes with the increase of aging degree.At the same time,there is a good correlation between the degree of polymerization and the refractive index,which shows that THz spectroscopy can be applied to the diagnosis of aging state of insulating oil paper.