换油对变压器油中糠醛含量和绝缘纸老化评估的影响及修正

为研究现场变压器换油后油中糠醛的变化规律及换油对使用油中糠醛评估绝缘纸老化的影响,在实验室对油纸绝缘样品进行130℃加速热老化,在老化的前、中、后期分别换油,对比换油前、后油中糠醛的含量。结果表明,换油后,油中糠醛大量损失;换油前、后油中糠醛含量的差值随老化时间的加长而逐渐减小;不考虑换油,直接使用油中糠醛评估绝缘纸老化会使评估结果偏高,误差在换油后初期尤其显著。定义在相同的老化时间换油后与换油前油中糠醛的比例为修正函数,研究了修正函数的变化规律,并用其对换油后油中糠醛进行修正。结果表明,使用修正函数可以有效改善换油后绝缘纸老化程度的评估效果。研究了修正函数向现场运行温度推广的方法,以利于现场变压器换油后的糠醛修正。

Effects and Corrections of Oil Replacement upon Furfural Content inInsulating Oil and Aging Assessment of Insulation Paper ofPower Transformers

In order to investigate the changing of furfural content in insulating oil after oil replacement and its effects on insulation paper aging assessment, accelerated thermal aging test of oil-paper insulation samples was conducted at 130℃ in the laboratory. The aged insulating oil was replaced at the early, middle and late aging stages respectively, and the furfural content in oil was compared. The results showed that the furfural content greatly declined after oil replacement. The difference of furfural content in oil before and after oil replacement decreased with aging. If oil replacement was neglected, the aging assessment of paper will cause over-estimation, especially at the early stage after oil replacement. Furfural modification function was defined as the ratio of furfural in oil at the same time point before and after oil replacement. The changing rules of furfural modification function were studied and used to correct the furfural content. It was shown that the modification function could effectively improve the aging assessment results. The furfural modification function was generalized to operation temperature, which can correct the furfural content of in-service transformers.