| Transformers are the key equipment of the power system and play an important role in the power generation and distribution.Keeping safe and reliable operation is the basis of ensuring the supply of electricity.The aging degree of paper insulation determines the operating life of transformers.Aging assessment of transformer paper insulation is of great significance to the operation and maintenance of transformers.In this thesis the changing mechanism of refractive index of cellulose fiber was studied during thermal aging,and the dispersive staining method was adopted to obtain the cellulose fiber dispersion staining images,and the relationship between image characteristic parameters and aging degree of paper insulation was obtained.The main contents are as follows.(1)The changing law of paper insulation aging characteristics was obtained during the thermal aging.Through the accelerated thermal aging experiments of oil-paper insulation at different temperatures,the changes of physical and chemical characteristics such as polymerization degree,furfural content in oil,carbon and oxygen gas in oil,moisture content and acid value were studied.The dispersion staining images were obtained,and the changing law of the dispersion staining color was studied with aging time incresing.The results showed that the dispersion staining color is mainly blue at initial stage of aging.With the increase of aging time,the blue component decreases,and purple component gradually appear.The blue component decreases ulteriorly and the purple component increases inversely.Red component appeares in the end of thermal aging experiment.(2)The changing mechanism of refractive index of cellulose fiber was analyzed.The molecular simulation software was adopted to analyze the amorphous structure parameters to obtain the changing law of bulk density in amorphous zone of cellulose fiber.Through the simulation analysis of the refraction index of cellulose fiber,the cellulose fiber dispersion curves were obtained in different simulation times,and the change law of the polarization degree was obtained with the simulation time.The relationship between the refraction index and the polarization degree was analyzed,and the intrinsic reason for the change of the refraction index of cellulose fiber was obtained during the thermal aging process.The results showed that the first peak of the double body distribution function and the ordered domain size gradually increases.The decrease of the average atomic displacement indicates the expansion of the ordered range.The recrystallization phenomenon is indicated that the bulk density is increased.During the thermal aging process,the refractive index of the cellulose fiber increases gradually,while the inclination angle of the dispersion curve decreases gradually.The degree of polarization also increases.In summary,the increase of bulk density and polarization leads to the increase of refractive index during the thermal aging process.(3)The characteristic extraction method and characteristic parameters of cellulose fiber dispersion staining images were proposed.In order to extract the images of aging characteristic parameters,the cellulose fiber dispersion staining images were preprocessed.The statistical characteristics of the three primary color ratios and color inhomogeneity of the dispersion staining image were analyzed.Then the relationship between statistical characteristics and degree of polymerization was obtained.Finally the support vector machine was used for cellulose fiber identification to prove the rationality of characteristic parameters selection.The results showed that the mean value of b decreases,while the mean value of r increases with the increase of aging time.The color inhomogeneity increases at initial stage and then the color inhomogeneity decreases.When the degree polymerization of paper insulation is the same,the color inhomogeneity is significantly different. |
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