| Oil-paper insulation is the main form of insulation in oil-immersed power transformers.The aging of oil-paper insulation is the main cause of power transformer failure.Nomex insulation paper has been widely used in dry-type transformer insulation due to its good mechanical properties,thermal stability and electrical properties,but its insulation performance for oil-immersed transformers needs further attention;Partial discharge as a non-destructive electrical diagnosis method has been widely recognized in the practice of insulation aging diagnosis in power transformers,however,partial discharge has strong randomness,and it is necessary to further discover new characteristics of partial discharge to improve the recognition efficiency of insulation aging state..This paper carries out the thermal aging test of Nomex insulating oil paper in the laboratory,and analyze the gas characteristics and partial discharge characteristics of oil in the thermal aging process of Nomex insulation oil paper,and identify the thermal aging state of Nomex insulation oil paper,which has important theoretical significance and engineering value to guide the aging evaluation of new insulation materials for power transformers.Thesis includes the following main content:(1)The gas production characteristics of Nomex insulation paper in oil during thermal aging were studied.The trend of the evolution of various dissolved gases with ageing in mineral insulation oil and vegetable insulation was analyzed,acqurie the main characteristics of dissolved gas of Nomex paper during heat aging process;Perform a traditional DGA three-ratio analysis on oil-paper insulation fault conditions with excessive total hydrocarbon content to acquire the applicability suggestion of three-ratio method for fault diagnosis of Nomex insulation paper.(2)The partial discharge characteristics of Nomex insulation paper with thermal aging were studied.The initial discharge and breakdown voltages,PRPD spectra,and their statistical discharge characteristics of the insulating papers with aging were analyzed.The partial discharge characteristics of Nomex insulation paper and traditional kraft insulation paper during thermal aging were compared and analyzed.The partial discharge characteristics of Nomex insulation paper developed with heat aging were obtained.(3)Using the partial discharge galactic co-occurrence matrix texture feature,the aging state of Nomex oil-paper insulation was identified.Based on the partial discharge patterns of different aging stages of Nomex insulation paper,a corresponding two-dimensional matrix of partial discharge distribution is constructed,and the gray level co-occurrence matrix of the twodimensional matrix is calculated;Extract the texture features of the gray level co-occurrence matrix,analyze the extracted texture features using principal components,and reduce the dimension of the feature;Use the genetic algorithm to optimize the parameters of the support vector machine model,classify and identify the extracted partial discharge texture features,and determine the thermal aging state of Nomex oil-paper insulation. |
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