Study On Aging Assessment Model Of Transformer Insulation Paper Based On Methanol In Oil And Modification Of Influencing Factors

Oil-paper insulation is an important part of power transformer,and its aging state directly affects the safe operation of transformer.The degree of polymerization(DP),which is an important parameter reflecting the aging state of insulation paper,decreases gradually during the aging process.Methanol,as a characteristic by-product of aging degradation of insulation paper,can effectively reflect the change of DP of insulation paper.Therefore,this dissertation carried out experimental research in the laboratory,based on the detection of methanol content in oil,established an assessment model that can effectively reflect the DP of insulation paper,and provided theoretical guidance for the aging state assessment of insulation paper.Thermal aging experiment of oil-paper insulation were carried out to study the changes of DP and methanol content in oil during the aging process,and an assessment model of oil-paper aging state based on methanol in oil was established based the degradation kinetics of cellulose.The results show that with the aging time increasing,the DP of insulation paper decreases,slows down and eventually tends to be constant,and the methanol content in oil increases,slows down and finally tends to saturation.According to the analysis of the theory of assessment model,the conversion mechanism between cellulose degradation and generation of methanol was clear.In the amorphous region,the methanol conversion amount increased rapidly first and then tended to saturation with the degradation of cellulose.In the crystalline region,the methanol conversion amount maintained a linear increase with the degradation of cellulose,and its conversion rate was lower than that in the amorphous region.In order to improve the applicability of the assessment model under different operation conditions,the influence of temperature and moisture content of insulation paper on methanol in oil was studied,and the assessment model was modified by establishing the temperature and moisture correction relationships of methanol content in oil.The results show that methanol content in oil is positively correlated with temperature,and the higher the aging,the more obvious the influence of temperature on methanol content in oil.The methanol content in oil is positively correlated with the moisture content of insulation paper,and the higher the temperature,the more obvious the influence of moisture on the methanol content in oil.Considering the influence of transformer oil-replacement on assessment model,the influence of oil-replacement in different aging stages on methanol content in oil and degradation of insulation paper was studied.The results show that there is a large loss of methanol in oil after oil-replacement,and the later the oil-replacement period is,the larger the gap with the oil without replacement,but the influence of oil-replacement decreases gradually as the aging continues.Meanwhile,oil-replacement can inhibit the degradation rate of insulation paper and help to slow down the decline trend of DP of insulation paper.Based on the above rules,the correction relationship of methanol and DP under oil-replacement was established,which to modify the assessment model.