油纸绝缘微水二次扩散过渡过程的分析

以菲克第二定律为基础建立数学模型,分析了变压器油纸绝缘纸中水分一次扩散未达到稳态时,外部条件改变导致绝缘纸中稳态水分含量改变,进而引发的绝缘纸中水分发生二次扩散过程。重点分析了由于一次扩散不充分引起的二次扩散过程中的过渡过程,并进行了实验验证。提出表征二次扩散过渡过程的特征量,即过渡时间和相对误差。过渡时间是从二次扩散开始到绝缘纸中水分扩散方向处处一致的时间,受温度、纸厚和一次扩散平衡率的独立作用;相对误差是以一次扩散水分均值作为二次扩散水分起始分布造成的误差,相对误差峰值表征二次扩散过渡过程的强度,受一次扩散平衡率、二次扩散稳态水分含量影响,相对误差峰值时间表征二次扩散过渡过程的速度,受温度和纸厚的影响。

Analysis of Transition Process During Secondary Diffusion of Moisture in Oil-Paper Insulation

On basis of Fick's second law, a mathematical model is established to analyze the secondary diffusion process of moisture in oil-paper insulation. The secondary diffusion occurs when the external conditions change during the first diffusion. Analysis focuses on the transient process during secondary diffusion, which is initiated by the insufficiency of the first diffusion and is verified by experiments. Two features of the transient process are proposed, namely transition time and relative error. Transient time is the time from the beginning of secondary diffusion to the time when the moisture diffusion direction is consistent everywhere. Transient time is independent of the temperature, paper thickness and the balance ratio of the first diffusion. Relative error emerges when the average moisture content of first diffusion is used as the initial distribution of secondary diffusion. The peak of relative error represents the strength of the transient process, which is influenced by the balance ratio of the first diffusion and steady moisture content. The peak time of relative error represents the speed of transient process, which is influenced by the temperature and paper thickness.