纤维素老化对油纸绝缘水分扩散特性的影响机制

Influence of Cellulose Aging on Characteristics of Moisture Diffusion in Oil-paper Insulation

大量变压器进入运行的中后期,绝缘纸老化会对油纸绝缘水分平衡产生影响。试验测试了绝缘纸在空气中、油纸绝缘体系中的水分平衡过程。实验结果表明,相同空气湿度下,绝缘纸聚合度越低,其吸附的水分含量越高;油纸绝缘中,绝缘油中水分含量相同时,绝缘纸聚合度越低,水分向绝缘纸中迁移速率越快,其稳态水分含量越低。绝缘纸老化所发生纤维素微观特性的变化表明空气中老化绝缘纸无定形区增大,聚合度降低,附着在绝缘纸孔隙中的亲水性杂质导致其吸水性增加;油纸绝缘中,老化绝缘纸的无定形区孔隙、纤维素内的孔隙由于绝缘油分子的进入导致间接吸附水的减少,亲水性杂质溶解于油中,比表面积的下降导致亲水基团的减少使得吸附水分的含量降低。最后,将文中实验所得曲线与类Oommen曲线类比,聚合度对油纸绝缘水分平衡的影响可以认为在横坐标方向对类Oommen曲线的平移。

A large number of power transformers within electric utilities approaching the end of their design life, insulation paper aging will affect the moisture equilibrium in oil-paper insulation. Moisture equilibrium of insulation paper in air and oil-paper system were tested. Experimental results show that the lower degree of polymerization of insulation paper is, the higher moisture content is adsorbed at same air of relative humidity and the faster migration rate of moisture into insulation paper, but the lower steady-state moisture content in insulation paper in oil-paper insulation. Microscopic characteristics of aging cellulose： extended amorphous area, reduction of degree of polymerization （DP） and increased hydrophilic impurities attached to insulation paper lead to rise of moisture absorption of insulation paper in the air. In oil-paper insulation, pores in amorphous paper and cellulose filled with oil molecules causing reduction of indirect adsorption moisture, hydrophilic impurities dissolved in oil and the lower hydrophilic group caused by decreasing specific surface area reduce the moisture content in insulation paper. Finally, comparison experimental curves with the Oommen-class curves indicates that influence of cellulose aging on moisture equilibrium in oil-paper insulation could be simplified as Oommen-class curves shift in the abscissa direction.