Study On Characteristics Of Dispersion Staining Color Of Cellulose Fiber Correlated With Thermal Aging Of Transformer Paper Insulation

Transformers are the key equipment of the power system,and their safe and stable operation determines the reliability of the power system.The lifetime of paper insulation determines that of transformers and aging assessment of transformer paper insulation is of great significance to the operation,maintenance,examine and repair,and retirement of transformers.In this thesis the dispersion staining method was adopted to investigate the characteristics of dispersion staining color of cellulose fiber and the aging markers for paper insulation based on the dispersion staining color of cellulose fibers in oil were proposed.The main contents are as follows.(1)The changing law of refractive index of insulating paper and cellulose fiber during the thermal aging was obtained.By performing the accelerated thermal aging experiments of oil-paper and cellulose fiber,the changing law of crystallinity and refractive index of insulating paper and the changing law of crystallinity of cellulose fiber were studied.The changing law of refractive index of cellulose fiber was studied with the dispersion staining method.The results showed that the crystallinity and refractive index of insulating paper and the crystallinity of cellulose fiber increase with the increase of aging time.The average refractive index of cellulose fiber also increases with the increase of aging time,which was indicated by the changing law of its dispersion staining color.(2)The mechanism of increase in refractive index of insulating paper and cellulose fiber was analyzed.The changing law of state of aggregation of crystalline regions and amorphous regions of cellulose during the thermal aging was investigated and its influence on crystallinity was analyzed.The changing law of degree of order of amorphous regions of cellulose during the thermal aging was studied with a molecule simulation software.The correlation between refractive index and crystallinity was analyzed,and the mechanism of increase in refractive index was obtained.The results showed that the recrystallization of amorphous regions of cellulose and the subsequent increase of the degree of order are the main reasons that increase the crystallinity of cellulose fiber.The increase in the ordered domain size further confirms the recrystallization of amorphous regions of cellulose.The refractive index of paper and cellulose fiber is positively correlated with its crystallinity and therefore it increases during the thermal aging.(3)The changing law of fiber morphology and the law of paper fiber abscission during the thermal aging were studied.The characteristic of surface fiber damage and rupture of paper was studied with a scanning electronic microscope.The changing law of fiber length,width,their corresponding distributions,and the shape factor of fiber were analyzed with a fiber tester.The abscission law of fiber from paper and the influence of temperature and initial moisture content of paper on it were studied,and the correlation between the number of cellulose fibers in oil and the average number of chain scissions per cellulose chain was found.The results showed that the ratio of long cellulose fibers decreases while that of short cellulose fibers increases during the thermal aging.The ratio of long fibers in oil decreases while that of short fibers in oil increases,and the number of fibers in oil exhibits a linear relationship with the average number of chain scissions of paper.The temperature and initial moisture content of paper have significant influence on the number of cellulose fibers in oil.(4)The aging markers of paper insulation based on the dispersion staining color of cellulose fiber in oil were proposed.The changing law of average value of primary color ratio of red and blue of dispersion staining images were found by observing and analyzing the dispersion staining color of cellulose fibers.The aging markers based on dispersion staining color were proposed.The mathematical models revealing the relation between degree of polymerization of paper and the proposed aging markers,as well as the relation between aging time of paper and the proposed aging markers were established.The applicability of the proposed aging markers after oil replacement was evaluated by conducting oil replacement in accelerated thermal aging experiment for oil-paper insulation.The results showed that the average red primary color ratio of the dispersion staining images of cellulose fibers increases while the average blue primary color decreases with the increase of aging time.The proposed aging markers is capable of reflecting the aging degree and aging time of insulating paper and they also apply to the aging assessment of insulation paper after an oil replacement was conducted.The above research work is an active exploration in aging assessment of transformer paper insulation.The research findings provide theoretical and experimental basis for the aging assessment and life prediction of transformer paper insulation.