油纸绝缘水分迁移特性研究综述

Review on Moisture Migration Characteristics of Oil-paper Insulation

油纸绝缘作为电力变压器的主要绝缘形式,其绝缘性能与水分含量密切相关,准确获得油纸绝缘的水分含量对变压器故障预警至关重要。在油浸式变压器内部电场、温度场等多物理场梯度的驱动下,水分始终处于动态迁移过程中,时空分布复杂,难以直接测量,因此需深入研究水分迁移特性。文中综述了油纸绝缘水分迁移机理、模型及特性研究上取得的成果:水分迁移是不同存在形式的水分子与绝缘油纸微观结构相互作用的过程,受多物理场的影响显著。现有油纸绝缘水分迁移研究多基于Fick定律,利用扩散系数表征水分梯度及温度对水分扩散速度的影响,但未能深入耦合多物理场的作用,不能获得温度梯度下的水分不均匀分布特性。研究获得了材料性质、温度、电场等多因素作用下扩散系数的变化规律及相应水分迁移过程,但将影响因素耦合于扩散系数的方式不能准确描述多物理场对水分迁移的作用,且缺少电场作用下的宏观水分迁移规律研究。根据驱动势平衡原理建立的热湿耦合模型能够描述水分的时空分布,量化电场对水分动态迁移特性的影响。进一步需推进基于水分时空分布无损测量的实验研究,深化多物理场耦合下水分迁移建模,构建多物理场下理论体系,以准确表征油浸式变压器中油纸绝缘水分迁移的时空分布。

The insulation performance of oil paper insulation,as the main insulation form of power transformer, is closely related to the moisture content. Accurately obtaining the moisture content of oil paper insulation is crucial for transformer fault early warning. Driven by the gradient of multiple physical fields such as electric field and temperature field inside the oil immersed transformer, the moisture is always in the process of dynamic migration, and the spatiotemporal distribution is complex, which is difficult to measure directly. Therefore, it is necessary to study the characteristics of moisture migration. This paper summarizes the research results on the mechanism, model and characteristics of moisture migration in oil paper insulation as follows: moisture migration is a process of interaction between water molecules in different forms and the microstructure of insulating oil paper, which is significantly affected by multiple physical fields. The existing research on moisture migration in oil paper insulation is mostly based on the Fick’s law. The diffusion coefficient is used to characterize the influence of moisture gradient and temperature on moisture diffusion velocity, whereas they failed to deeply couple multiple physical fields, and the uneven distribution characteristics of moisture under the temperature gradient can not be obtained. The change law of diffusion coefficient and corresponding moisture migration process under the multiple factors such as material properties, temperature and electric field are obtained. However, the way of coupling influencing factors to diffusion coefficient can not accurately describe the influences of multi-physical fields on moisture migration characteristics, and there is a lack of research on moisture migration law under the electric field. The heat moisture coupling model based on the principle of driving potential balance can describe the spatiotemporal distribution of moisture and quantify the influence of electric field on the dynamic migration of moisture. It is necessary to further carry out the experimental research based on the nondestructive measurement of moisture spatiotemporal distribution,deepen the modeling of moisture migration under the coupling of multi-physical fields, and build a theoretical system under multi-physical fields, so as to accurately characterize the spatiotemporal distribution of moisture migration of oil paper insulation in oil immersed transformer.