基于分子动力学模拟的油纸绝缘系统中气体小分子扩散行为

Diffusion Behavior of Gas Molecules in Oil-paper Insulation System Based on Molecular Dynamic Simulation

为了从微观层次上揭示气体小分子在变压器油纸绝缘系统中的扩散机理,对变压器油纸复合绝缘材料老化过程中产生的7种常见气体小分子(包括H2、CO、CO2、CH4、C2H2、C2H4和C2H6)在油纸两相介质中的扩散行为进行了分子动力学模拟。采用分子动力学模拟软件,搭建了2组模型,以分别模拟各种气体小分子在油中和纤维素绝缘纸中的扩散。通过对气体小分子在油纸介质中扩散系数、位移特性、自由体积特性与油纸的相互作用能的研究,考察了不同气体小分子在油纸介质中扩散的微观机理,探讨了气体小分子在油纸介质中扩散特性的差异,比较了不同因素对气体小分子扩散行为的影响。研究发现:气体小分子在纤维素中的扩散系数比其在绝缘油中的扩散系数小1个数量级,且7种气体小分子在2种介质中的扩散系数的排列顺序亦不相同;在绝缘油中,主要影响气体小分子扩散行为的是自由体积;而在纤维素材料中,对气体小分子的扩散行为起主要影响的是分子间的相互作用。

In order to reveal the diffusion mechanism of gas molecules in transformer oil paper insulation system on the micro level, diffusion behaviors of 7 kinds of gas molecules in oil and paper medium were simulated based on molecular dynamics, respectively. The gases includes H2, CO, CO2, CH4, C2H2, C2H4, and C2H6, which are commonly utilized in dissolved gas analysis of power transformer and produced during the aging process of oil paper composite insulating material. By using a molecular dynamics simulation software, 2 groups of models were set up to simulate the diffusion of the gas molecules in oil and paper. By investigating the diffusion coefficients, displacement features, free volume characteristics, and interaction energies of corresponding gas molecules, the diffusion micro-mechanism of the gas molecules was observed, the differences in diffusion features among the gas molecules were discussed, and the influences of impact factors on gas molecules＇ diffusion were contrasted. Simulation results indicate that the diffusion coefficients of gas molecule in cellulose is an order of magnitude lower than that in oil, and the order of the diffusion coefficients of these gas molecules in the 2 kinds of insulation media is different. It is concluded that, in oil, the main factor influencing the gas molecular diffusion behavior is the free volume of gas molecules, and in cellulose, this main factor is the intermolecular interaction.