基于油中水分含量的变压器绝缘纸寿命评估

Life Expectancy Evaluation of Transformer Insulation Paper Based on Moisture Content in Oils

水分是影响电力变压器油纸绝缘性能的重要因素,如何通过油中水分含量简单、准确地判断变压器绝缘纸的老化状态成为当今研究的重点。本文首先分析了油纸绝缘系统的水分来源及其危害,然后基于频率因数a的Taylor展开式得出a与绝缘纸中水分含量间存在正比关系,进而得到了计及水分含量的修正Arrhenius定律。其次,结合化学反应动力学推得绝缘纸中水分含量与聚合度间的量化关系,并根据纤维素老化对Oommen油纸水分平衡的影响,获得了绝缘纸的聚合度（degree of polymerization,DP）与油中水分含量间数量关系的修正表达式;在此基础上推得了绝缘纸特征寿命的预测判据。最后,通过实验数据表明未考虑绝缘纸老化影响时,油纸水分与纸中水分间的表达式的计算误差为20%～50%,基于油中水分含量的DP表达式的计算误差为3.8%～38.4%;而修正表达式可分别将上述误差降低到12.5%以下及23.3%以下。当老化温度为140℃,油中水分的体积分数分别为10^（-6）和13×10^（-6）时,绝缘纸的特征寿命分别为65天和12天。

Moisture is a key factor affecting the insulating property of transformer oil-paper insulation and many current research efforts have focused on resolving the relationship between its insulation state and the moisture content in the oil. Firstly, the source and harm of moisture in the oil-paper insulation system were analyzed, and the proportional relationship between the frequency factor a and moisture content in the insulation paper was deduced based on the Taylor expansion of a, and then the modified Arrhenius law was obtained in which the moisture content was taken into account. Secondly, the quantitative expression moisture content in the insulation paper and degree of polymerization（DP） was obtained by chemical reaction kinetics, the modified expression between DP and moisture content in the oil was derived according to the influences of cellulose aging on the Oommen＇s moisture equilibrium curves, and the rectified representation between DP and the moisture content in the oil was acquired. Thereby, the characteristic life prediction criterion of the insulation paper was concluded. Finally, the validity of the proposed method was verified by experimental data. The results show that the calculation errors of the expression between moisture content in insulation paper and oil are between 20% and 50% without considering the aging of insulation paper and the errors of DP based on the moisture content in oil are between 3.8%～38.4%, but the above errors will be reduced to 12.5% and 23.3%, respectively, if they are calculated with the modified expressions. When the aging temperature remains at 140 ℃ and the moisture content in the oil is 10^（-6） and 13×10^（-6）, respectively, the insulation paper characteristic life will be 65 d and 12 d, respectively.