| At present,most energy bases in China are far away from load centers.Large-capacity long-distance power transmission has become one of the major issues of electric power development in China.DC GIL has been widely used because of its closed coaxial metal pipeline structure,which has natural advantages such as high voltage level,large transmission capacity,low electromagnetic radiation and flexible laying.However,its insulation failure is still the main cause of equipment failure.So far,the surface charge accumulation effect of insulators under DC voltage is still the main reason for the long-term stability of DC GIL.With the continuous development of HVDC UHV transmission technology in China,higher requirements are put forward for the physical properties of epoxy casted basin insulators and pillar insulators in GIL.Therefore,the design and optimization of insulating materials with higher physical properties has become an urgent problem to improve the reliability of DC GIL insulation operation.In order to find an epoxy resin alternative material with higher physical properties to inhibit surface charge accumulation,In this paper,the research work based on molecular dynamics simulation method is carried out.The main contents include:Models of pure crosslinked epoxy resin and epoxy resin composites doped with carbon nanotubes and graphene and their functionalized modification are constructed.The physical properties of models such as dielectric constant,thermal diffusivity(thermal conductivity,specific heat capacity),mechanical properties and glass transition temperature are simulated and calculated.The effects of one-dimensional and two-dimensional carbon nanomaterials and their functionalization on the properties of composites are investigated from the micro level.The main results are as follows:(1)The models of pure crosslinked epoxy resin and epoxy resin composites doped with four carbon nanotubes(unclosed,semi-enclosed,fully enclosed and aminoamine functionalized)are established by Materials Studio(MS).The physical properties of the composites are simulated and calculated under LAMMPS.The results show that the properties of epoxy resin composites doped with the four carbon nanotubes are improved,but the degree of promotion varies.Among them,the mechanical properties,dielectric constant and thermal diffusivity of the composites doped with aminoamine functionalized carbon nanotubes increase most obviously,including restraining the damage of temperature rise to mechanical properties,reducing dielectric constant by 24.8%,increasing thermal diffusivity by 96.98%.The composites doped with full-end carbon nanotubes only increase glass transition temperature by 25.7 K to the greatest extent,while the other key physical properties are not significantly improved.Based on the simulation results,it is concluded that the choice of aminoamine functionalized carbon nanotubes as epoxy resin doped particles is more in line with the demand of surface charge accumulation inhibition.(2)The model of epoxy resin composites doped with four kinds of graphene(unmodified,carboxyl,hydroxyl and amino functionalized)is established by MS,and their physical properties are calculated by LAMMPS.The results show that the properties of epoxy resin composites doped with graphene are improved.Among them,the dielectric constant and thermal diffusivity of the composites doped with hydroxyl functionalized graphene increase most obviously,and the dielectric constant decreases by 30.7%and the thermal diffusivity increases by 55.7%.The glass transition temperature of the composites doped with carboxyl functionalized graphene increases the most.which is 63.98 K higher than that of pure epoxy resin.In the modification of graphene,hydroxyl functionalized graphene is selected as the doped particle to obtain epoxy resin composite,which can optimize the dielectric constant,thermal diffusivity and mechanical properties to the greatest extent.It is an alternative material to inhibit surface charge accumulation.(3)Comparing the epoxy resin composites doped with carbon nanotubes and graphene,it is found that the relative dielectric constant of the graphene-doped epoxy resin composite model systems decrease more,and the average value is reduced by 8.9%compared with the pure epoxy resin,which indicated that graphene is more suitable as a doping particle for reducing the dielectric constant of the composite.The thermal conductivity of composites doped with hydroxyl functionalized graphene is lower than that of doped aminoamine functionalized carbon nanotubes,which indicates that one-dimensional carbon nanotubes have greater advantages in heat conduction than two-dimensional graphene.Carbon nanotubes can greatly improve the heat transfer efficiency of composite materials in specific directions.In terms of mechanical properties,the composite models doped with carbon nanotubes and graphene are basically consistent with pure epoxy resin,and the bulk modulus is improved.Compared with pure epoxy resin,the glass transition temperature of the composite model doped with carboxyl functionalized graphene increased by 63.98 K,and the glass transition temperature of the composite model doped with full-capped carbon nanotubes increased by 25.7 K.The glass transition temperature and thermal stability of the composites can be improved more obviously by doping graphene than by doping carbon nanotubes.Considering comprehensively,it is considered that the physical properties such as dielectric constant,thermal diffusivity,mechanical properties and glass transition temperature can be improved to the greatest extent by using graphene as nano-doped particles.Among them,the epoxy resin composite model doped with hydroxyl functionalized graphene is the best one,which is an alternative material to inhibit surface charge accumulation.Based on molecular dynamics simulation,the key physical properties of epoxy resin composites were calculated.The results obtained provide theoretical basis and technical support for doping design,screening and performance control of epoxy resin nanocomposites for DC GIL insulators. |
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