初始水分含量对油纸绝缘热老化特性的影响

为探讨初始水分含量对变压器油纸绝缘老化过程的影响机制,设计了绝缘纸初始水分质量分数分别为1%、3%、5%的矿物油-纸绝缘试品在90°C下的加速热老化试验,定期取样测量了绝缘纸聚合度、油纸绝缘水分质量分数、油中糠醛质量浓度、油中酸值等特征参量。然后,在分子模拟软件内建立了不同含水量的矿物油分子、糠醛分子、水合氢离子模型,通过分子动力学模拟技术计算了糠醛分子及水合氢离子与不同水分含量油分子模型之间的扩散系数、相互作用能、径向分布函数。实验结果表明:绝缘纸和矿物油中水分含量在老化过程中均是波动的,油中糠醛和酸值在老化过程中的变化趋势未与绝缘纸聚合度的下降规律相对应,受系统水分含量的影响较大。分子模拟结果表明:水分的增加显著降低了糠醛及小分子酸的扩散能力,并与糠醛及小分子酸形成稳定的氢键;同时,水分与糠醛及小分子酸的极性作用改变了彼此的相互作用能。实验数据与分子模拟结果相互验证,为深入研究油纸绝缘的老化机理及诊断提供了理论参考。

Influence of Initial Moisture on Thermal Aging Characteristics of Oil-paper Insulation

The mineral oil-paper samples with different initial moisture contents(1%,3%,and 5%) were thermally aged under 90°C in order to study the influence of the mechanism of initial moisture on thermal degradation process of oil-paper insulation.All the samples were periodically sampled and the degree of polymerization(DP) of insulation paper,the moisture content of oil-paper samples,furfural,acid in oil,and so on were measured during the aging process.Moreover,by using a material simulation software,oil molecule with different moisture contents,furfural molecules and hydroniumions were modeled,respectively.Then,diffusion coefficients,interaction energies,and radial distribution function among furfural molecule,hydroniumion and oil molecules with different moisture contents were calculated based on dynamic molecular simulation technology.The obtained results show that moisture in both oil and paper is fluctuant during the aging process.Additionally,furfural and acid in oil,which do not correspond with the decrease of DP,are markedly influenced by the moisture of oil-paper system.Molecular simulation results reveal that the increased moisture can not only reduce the diffusion capability of furfural and hydroniumions,but also result in more stable hydrogen bonds between moisture and furfural & hydroniumion.Meanwhile,the interaction energies between moisture and furfural & hydroniumion have been changed due to the mutual polar effect of moisture and furfural & hydroniumion.The experimental results and molecular simulation results agree with each other,and the relevant results can provide theoretical reference for in-depth study on the aging mechanism and diagnosis of oil-paper insulation.