【作者】 王伟；

【导师】 李成榕；

【作者基本信息】 华北电力大学 ， 高电压与绝缘技术， 2012， 博士

【摘要】 运行年限较长的变压器中发现了较多的沿面爬电现象,老化程度和水分含量的增加被推测为导致这种现象的原因。但现有理论与研究成果尚无法很好的解释这一现象,原因在于试验数据表明老化对纸板的击穿特性没有影响,并且故障变压器中的平均水分含量也未超过标准限值。因此,需对老化与水分对油纸绝缘沿面爬电的影响开展进一步研究。这对于揭示老化与水分在沿面爬电发展中的作用,深入理解沿面爬电现象,预防变压器事故,具有重要的意义。为研究老化对油纸绝缘沿面爬电的影响,制备了不同老化程度的绝缘纸板试样,对试样进行了击穿电压试验与沿面爬电试验,对比分析了不同老化程度纸板的击穿电压、爬电起始、熄灭电压、耐受时间、击穿通道长度、白斑发展速度的差异,通过光学显微镜及SEM电镜研究了不同老化程度纸板层间及表面微观结构。发现了老化纸板中爬电具有更快发展速度的现象,提出并验证了老化导致的纸板层间方向孔洞体积及数量的增加是引起这种现象的主要原因。该结果表明,老化不仅影响纸板的机械性能,而且影响纸板的电气性能。为研究变压器中局部高水分区的形成原因,试验研究了变温条件下水分在油、纸间的迁移过程,分析计算了稳态及变温条件下,水分在纸板层间方向的分布规律,发现了油、纸交界面处油层在升温过程中,纸板表层在降温过程中可以形成高水含量区的现象；制备了不同老化程度的油与纸板,测量了不同老化程度油、纸板组合中的水分分布,发现了老化纸板纤维比表面积下降进而导致其吸湿能力下降的现象,该现象会导致老化变压器油中水分含量的进一步升高。为研究水分对沿面爬电的影响,基于水分在不同介质中的平衡原理,制备了不同水分含量的油试样与纸板试样,试验研究了水分含量与水分子状态对油纸绝缘沿面爬电的影响,观测并分析比较了油中水分与纸板中水分对沿面爬电影响的差异。研究结果表明：油中水分含量的增加会显著降低爬电的起始电压,但对爬电的发展速度没有影响；纸板中水分含量的增加不但会降低爬电的起始电压,还会导致沿面爬电速度的增加；纸板表面游离态水的出现是导致低场强、长间隙沿而爬电快速发展的主要原因。测量了沿而爬电发展过程中产生的脉冲电流信号,特高频信号,超声波信号及油中溶解气体,对各检测量的变化规律进行了统计分析,提出了沿面爬电严重程度的诊断方法更多还原

【Abstract】 Creepage discharge were found in many power transformers which serviced a long time, aging and increase of moisture were respected as the reason. However, present theories and results cannot explain the phenomenon well, because test results show there no impact of aging on breakdown voltage of pressboard and moisture constant of failure power transformers was still less than the limit value. So, impact of aging and moisture on creepage discharge on oil immersed pressboard should be researched deeply, which is very important to indicate the function of aging and moisture in creepage discharge, comprehend the phenomenon of creepage discharge and prevent the accident of power transformer.To research the impact of aging on creepage discharge, various aged pressboard samples were prepared, breakdown voltage and creepage discharge tests were carried out, breakdown voltage, creepage discharge inception voltage, extension voltage, enduring time, breakdown channel length and white mark development velocity were analyzed and compared, microstructure in normal direction and layer direction of various aged pressboards were observed by microscope and SEM. The results show that creepage discharge in cellulose layer for aged pressboards has higher average developing velocity compared to that for un-aged pressboards, which is related to the increase of cavity density and size between cellulose layers induced by thermal aging process. This finding indicates that the thermal aging not only may decrease the mechanical stress of the pressboard, but also may decreases creeping discharge stress in cellulose layer.To find out the condition of partial high moisture area generation, moisture move between oil and pressboard in warming and cooling process was researched, moisture distribution in pressboard layer direction was analyzed and calculated. The results show the high moisture area will generate in oil in warming process and generated in pressboard surface layer in temperature cooling process.Various aged oil and pressboard sample were prepared, moisture constant in oil and pressbord were measured. The results show the aged pressboard has lower moisture absorption. This is related to the decrease of specific surface area of celloluse induced by the thermal aging process. This finding indicates that moisture in oil will increase in age power transformer.To research the impact of moisture on creepage discharge, various moisture constant oil samples and pressboard samples were prepared according the moisture equilibrium mechanism in different media, the impact of moisture constant and water form on creepage discharge were observed and analyzed. The results show increase of moisture in oil will down the creepage discharge inception voltage signally, but has no effect on creepage discharge development velocity; increase of moisture in pressboard will both down the creepage discharge inception voltage and increase the creepage discharge development velocity; Formation of pretreated water is the main reason of creepage discharge decelop repidly under lower electric stress and long distance condition.Current impulse signal, UHF signal, acoustic signal and dissolved gases generated by creepage discharge were measured, their trends were analyzed, severity diagnostic method for creepage discharge was present.更多还原