Molecular Dynamics Simulation On DC GIL Physical Properties Of Epoxy Resin Doped With Functional Carbor Nanotubes

Large-capacity and long-distance HVDC transmission technology is one of the major issues in my country’s power development in recent years,and it is one of the important technical approaches to meet my country’s current power demand for load centers far away from energy bases.Gas-insulated metal-enclosed transmission line(GIL)is a new type of power transmission mode and an important part of HVDC transmission technology.However,the insulators of the DC GIL will be affected by the unipolar electric field during operation,and it is easy to accumulate charges on the surface of the insulator,which will cause the local electric field to be distorted.Eventually,this could cause the insulator to flashover along the surface,which endangers the long-term safe and stable operation of the DC GIL.Therefore,it is of great significance to improve the insulation operation reliability by optimizing and improving the physical properties of the insulation material.In order to find an epoxy resin nanocomposite with excellent thermal properties and other properties(on the premise of good mechanical properties,with higher thermal diffusivity,higher thermal conductivity,lower specific heat capacity and higher glass transition temperature)and a small dielectric constant as the nanocomposite coating of the insulator to weaken the accumulation of surface charges,the key physical properties of epoxy resin/functional carbon nanotubes nanocomposites were simulated based on molecular dynamics simulation technology.The main research contents are as follows:(1)The molecular dynamics models of epoxy resin/functional ized carbon nanotube composites were constructed,which are as follows:pure crosslinked epoxy resin(EP/neat)model,and EP/neat doped with un-functionalized,amino amine functionalized,carboxyl functionalized,and hydroxyl functionalized carbon nanotubes models,wherein functionalized carbon nanotubes grafting four or eight functional groups,respectively.The construction of functionalized carbon nanotubes models are considered from three aspects:functionalized or unfunctionalized,type of functional group and number of grafting of functional group.Besides,the eight models were respectively relaxed to make them closer to the actual material,laying a model foundation for subsequent simulation calculations of various physical properties.(2)To explore the effect of doped with different functionalized carbon nanotubes on the dielectric properties of epoxy resin nanocomposite,based on the molecular dynamics simulation method,the dielectric constant of epoxy resin/functionalized carbon nanotube nanocomposite models were calculated using LAMMPS software.The calculation contains the dielectric properties at 300 K and the dielectric constant temperature characteristics at 260-400 K.The results indicate that the dielectric constant of the nanocomposite doped with carbon nanotube has decreased compared with EP/neat.The relative dielectric constant of the doped functionalized carbon nanotube model is lower than that of the doped unfunctionalized carbon nanotube model.Besides,the relative dielectric constant of the doped carbon nanotube system grafted with eight functional groups is lower than that of the grafted corresponding four functional groups.What’s more,in the comparison of the model grafted with the same number of functional groups,it is found that the dielectric constant of the sy stem doped with amino-amine functionalized carbon nanotube is relatively small.In the dielectric constant properties at 300 K,the relative dielectric constant of EP/AFCNT8 is the smallest,which is 2.218 and has 10.13%lower than that of EP/neat.For the dielectric constant temperature characteristics at 260-400 K,the comparison between the four doping models and EP/neat at each temperature point shows that the relative dielectric constant of EP/AFCNT8 decreases the most,with maximum reduction percentage 11.9%and the minimum reduction percentage 10.1%.(3)To explore the effect of doped with different functionalized carbon nanotubes on the thermal properties(including thermal diffusivity,thermal conductivity,specific heat capacity)and other properties(glass conversion temperature and mechanical properties)of epoxy resin/carbon nanotube nanocomposites,based on the molecular dynamics simulation method,the thermal properties and other properties of epoxy resin/functionalized carbon nanotube nanocomposite models were calculated using LAMMPS software.The results show that the physical properties of epoxy resin nanocomposites doped with carbon nanotubes are improved to different degrees,and the properties of epoxy resin nanocomposites doped with eight functional groups are better than those of models doped with four corresponding functional groups.EP/AFCNT8 shows the most obvious improvement in thermal conductivity,thermal diffusion coefficient and mechanical properties.The overall thermal conductivity and thermal diffusion coefficient increase by 54.92%and 67.30%respectively.EP/HFCNT8 has the highest glass conversion temperature with the increase of 69.47 K,and the increase of EP/AFCNT8 is 58.97 K,which is second only to EP/HFCNT8.EP/CFCNT8 has the most significant increase in bulk modulus and Young’s modulus at 400 K,which are 52.4%and 35.5%,respectively.Due to the cross-linking reaction between amino group and epoxy matrix,the increase in the modulus of EP/AFCNT8 is more obvious,which could better maintain good mechanical properties.In this paper,the key physical properties of epoxy resin/functional carbon nanotube composites were calculated based on molecular dynamics simulation.The results could provide data support for the preparation of alternative epoxy resin nanocomposites to inhibit the surface charge accumulation of insulators.