Basic Research On Aging Characteristics Of Transformer Oil Paper Insulation Based On Molecular Dynamics Simulation

Oil-paper insulation is the most basic and main form of combined insulation in power equipment such as oil-immersed power transformers.Although the Dissolved Gas Analysis in Oil?DGA?method is currently widely used,there are coding defects due to the three-ratio method Such problems limit the in-depth application of this method.Molecular simulation technology,as a specific form of modern scientific research simulation calculation method,reveals the microscopic dynamic characteristics of matter from the molecular and atomic levels,and has been applied and paid attention in many fields.This article aims to apply molecular simulation technology to reveal the movement mechanism of gas molecules in oil-paper insulation from a micro level,with a view to laying a theoretical foundation for the in-depth application of DGA method and the evaluation of oil-paper insulation aging.First,the molecular dynamics method is used to divide the main component MPIA fiber of Nomex insulating paper into a crystalline region and an amorphous region.The temperature ranges from 343K to 423K,from mechanical parameters,hydrogen bonding,chain motion,and free volume.The thermal stability of MPIA fiber is analyzed from multiple angles such as fractions.The results show that the thermal stability of the crystalline region of MPIA fiber is stronger than that of the amorphous region.At the same temperature,various modulus values in the crystalline region are about twice that of the amorphous region;the incompressibility,rigidity,resistance to elastic deformation and plasticity of the crystalline region are stronger than the amorphous region,but the ductility and toughness It is not as good as the amorphous region;the hydrogen bonding structure of the crystalline region is more stable,the free volume fraction is less than the amorphous region,and the thermal stability is stronger.Secondly,accelerated thermal aging experiments were conducted on Nomex paper-mineral oil and Nomex paper-vegetable oil combination insulation samples,and the characteristics of dissolved gas in the oil of mineral oil and vegetable oil during the aging process were analyzed.The results showed that under the same conditions,In addition to C₂H₂,the characteristic gas content at different aging stages is increasing.The gas production in vegetable oil is significantly higher than that of mineral oil,and the characteristic gas component content of the two is different,but the content of CO and CO₂ is more;The main characteristic gases in mineral oil and vegetable oil are CH₄ and C₂H₆ respectively;when using the CO₂/CO ratio to judge the aging of Nomex insulating paper,different types of insulating oil will affect the results;in the middle and late aging experiments,minerals The total content of dissolved gas hydrocarbons in oil and vegetable oil is basically the same;the analysis and comparison of characteristic gas by IEC modified three ratio method shows that the existing analysis guidelines for dissolved gas in oil are not applicable to the composite insulation system of Nomex insulation paper and vegetable oil,A new theoretical system needs to be established.Finally,the diffusion behaviors of seven characteristic gas molecules?H₂,CO,CO₂,CH₄ C₂H₂ C₂H₄,C₂H₆?produced in the combined insulation system composed of Nomex paper and mineral oil and vegetable oil were analyzed.Analyze from multiple angles such as diffusion coefficient,free volume fraction,and the interaction energy between gas and insulating medium.The preliminary results show that the diffusion coefficient of the characteristic gas molecules in mineral oil is the largest,and the diffusion coefficient in the MPIA fiber is the smallest,the magnitude of the two differs by an order of magnitude.For the same type of gas molecules,the larger the relative molecular mass,the smaller the diffusion coefficient,the weaker the diffusion capacity;the free volume fraction of gas molecules in the insulating medium is mainly determined by the Van der Waals radius of the gas;The interaction between the gas and the medium can be closely related;the initial position of the gas molecule is critical to its diffusion in the oil-paper composite insulation system.When CH₄molecules are diffused in the Nomex paper-mineral oil composite insulation system,most of the CH₄ gas generated in the fiber is gathered at the oil-paper interface,and a small part of the CH₄ generated in the oil will also diffuse to the fiber surface for attachment,and it is generally difficult to enter Inside the fiber,it is basically isotropic during the diffusion process.When C₂H₆ molecules are diffused in the Nomex paper-vegetable oil composite insulation system,the C₂H₆ produced in the fiber is always bound to the fiber,and a small part can diffuse to the oil-paper interface.The diffusion of C₂H₆ in oil-paper insulation system shows anisotropic properties.The electrostatic interactions in each model account for a small proportion of the total potential energy,and the Van der Waals interaction plays a major role.The research conclusions obtained by using molecular simulation technology in this paper greatly enrich the diffusion theory of gas molecules in oil-paper insulation,and provide a theoretical reference for the analysis of dissolved gases in transformer oil.It also lays a theoretical foundation for the evaluation of oil-paper insulation aging and fault diagnosis.