Research On The Improvement Of Mechanical Properties And Thermal Stability Of PMIA Insulation Paper Modified By Nano SiO₂

In the era of ultra-high voltage,the safe operation of power grid is facing higher requirements and more severe challenges.Large power transformer as one of the core equipment in power grid,its main internal insulation material is oil-paper insulation.During the operation of the transformer,oil-paper insulation will gradually aging.Because the insulating paper is wrapped on the winding,it is difficult to replace the insulation paper to solve the problem of aging.Therefore,it is of great significance to enhance the insulation performance of insulating paper to improve the service life of the transformer and ensure the safe operation of the whole power network.In recent years,using nano particles to modify insulation paper has become a research direction with great theoretical and practical significance.At present,the effect of nano particles modifying insulating paper is mainly researched by means of macroscopic test.Due to the limitation of the test,it is impossible to research the microscopic mechanism behind the macroscopic phenomenon.However,the molecular simulation technology can penetrate into the micro level to reveal the microscopic mechanism.Therefore,in this paper,the PMIA insulation paper is taken as the research object,and is modified by nano SiO₂ particles.The molecular dynamics simulation is used as the tool to research the mechanical properties and thermal stability of unmodified and modified models.The main conclusions are as follows:（1）The research on the selection of the force field shows that,compared with the PCFF force field,the deviation value of the mechanical parameters obtained by COMPASS force field is smaller,which shows that the simulation results obtained by COMPASS force field are more stable and reliable.（2）The research on the influence of different nano SiO₂ radius on mechanical properties and thermal stability of PMIA fiber shows that,with the increase of the radius of the nanoparticles,the binding energy between nano SiO₂ particles and PMIA fibers increases.The repulsive force is the main form of the interaction between the two.With the increase of temperature,the deformation resistance ability of unmodified and modified materials are decreased,while the ductility and toughness are enhanced.Nano SiO₂ particles can effectively improve the mechanical properties of PMIA fiber,the rigidity and the compressibility of the material are enhanced.Among the research models in this paper,the improvement effect of nano SiO₂ with radius of 6 ? on the mechanical properties and thermal stability of PMIA fiber is the best.（3）Through the combination of molecular dynamics simulation and experiment,the influence of different nano SiO₂ content on mechanical properties and thermal stability of PMIA fiber is researched.With the increase of temperature,the interaction between nano SiO₂ and PMIA fibers is weakened.The addition of nano SiO₂ particles can effectively improve the mechanical properties of PMIA fiber,and decrease the chain motion intensity of PMIA fiber.The nano SiO₂ with the addition of 1wt.% has the best improvement effect on the overall mechanical properties of the model.With the addition of nanoparticles,the degree of the chain motion is reduced,and the thermal stability of the model is improved.The experiment results of tensile strength of PMIA insulation paper shows that the tensile strength of the paper reaches the maximum value when the amount of nano SiO₂ is 1wt.%,which is 4.9% higher than that of the unmodified aramid paper.（4）The research on the influence of water on the mechanical properties and thermal stability of unmodified and modified models shows that,with the increase of water content,the deformation resistance of the PMIA fiber is weakened,and the plasticity and ductility are enhanced.The mean square displacement and free volume of the PMIA fiber increases with the increase of water content,that means the thermal stability of PMIA fiber is decreased.With the addition of nano SiO₂ particles,the rigidity,plasticity and thermal stability of the modified model are improved compared with the unmodified model.