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.