电力变压器用绝缘纸热老化微观机理的X射线衍射分析

Aging Micro-mechanism of Oil-paper Insulation in Power Transformers by XRD Analysis

温度是油纸绝缘老化的主要因素。笔者设计了油浸式电力变压器常用的普通牛皮纸和环烷基矿物油复合绝缘在90℃下长达370 d的热单因子老化试验。利用XRD(X射线衍射)定期测量不同老化状态的绝缘样品,对比分析了绝缘纸的聚态结构的变化情况,并深入讨论绝缘纸聚合度下降的动力学过程。研究结果表明:绝缘纸在老化过程中,纤维素氢键和糖苷键发生断裂,引起聚合度下降,结晶区遭受破坏,晶粒尺寸减小,导致纤维素分子间作用力减弱,热裂解活化能降低;老化过程中,绝缘纸纤维素晶体类型不变,聚合度的下降规律符合二阶动力学模型,相对结晶度的变化规律能很好地解释聚合度的变化规律。

Temperature plays the main role in oil-paper degradation.In order to study oil-paper aging mechanism,accelerated thermal aging experiments in laboratory were performed.Kraft paper and naphthenic mineral oil were thermally aged for 370 days at 90 ℃.The XRD under different aging conditions of insulation samples were periodically performed,the variation of supramolecular structure of the oil-paper with different aging conditions was investigated,and the kinetics of paper degradation was also discussed in detail.The results indicate that the degree of polymerization（DP） of the oil-paper is caused by breakdown of hydrogen and glycoside bonds,resulting in cellulose＇s inter-or inner-molecular force weakening and activation energy of pyrolysis decreasing.The crystal areas of cellulose are destroyed,and the crystal grain size decreases,and the crystal type keep stable during paper aging.The decreasing of DP coincides with the second-order kinetic model,and the decreasing law of DP can be well explained by relative degree of crystallinity.