Performance Of Silane Coupling Agent Grafted Hexagonal Boron Nitride (h-BN) Modified Cellulose Insulating Paper For Transformer

Rural power grid is an important infrastructure in rural areas.Strengthening rural power grid construction and continuously improving the quality of rural power supply is an important guarantee for fully serving rural revitalization.As one of the most important power equipment in the distribution(agricultural)network,the insulation performance of transformers is the key to ensuring the safe operation of the power grid.Therefore,the importance of insulation paper inside transformers is selfevident.During the long-term operation of transformers,insulation paper often deteriorates due to its internal thermal stress,mechanical stress,and electromagnetic field effects,affecting the operation of the transformer.Therefore,it is necessary to use insulating paper with excellent thermal stability,mechanical properties,and electrical properties to extend its life,thereby extending the service life of the transformer.Based on the wide application of nanoparticle modification technology in the field of composite materials,as well as the excellent performance of hexagonal boron nitride(h-BN)and silane coupling agent,this article chose to use nanoparticle h-BN and silane coupling agent grafted h-BN to modify cellulose insulating paper.In this paper,molecular simulation and experimental methods were used to establish pure cellulose model,different mass fraction h-BN modified cellulose model,and different silane coupling agent grafted h-BN modified cellulose model.Then,different mass fraction h-BN modified cellulose insulation paper and different silane coupling agent modified cellulose insulation paper were prepared,and the thermal stability,mechanical properties and electrical properties of several modified cellulose insulation paper was compared and analyzed to obtain a relatively optimal modification method.Finally,the performance of unmodified cellulose insulating paper and 2wt% KH550-h BN modified cellulose insulating paper was tested through a 60 day accelerated thermal aging test.The main conclusions are as follows:(1)The thermal stability,mechanical properties,and electrical properties of cellulose modified with different mass fractions of h-BN nanoparticles first raise and then decline with the mass fraction increase of h-BN,and the best doping is 2wt%.The simulation results show that when the mass fraction of nano h-BN in cellulose is 2wt%,the cohesive energy density and thermal conductivity of cellulose are increased by 48% and 40%,respectively,while the mean square displacement and free volume fraction are significantly decreased.This indicates that the doping of appropriate amount of h-BN can make the internal network connection of cellulose closer,the internal connection is not easy to be damaged at high temperature,and the cellulose maintains good thermal stability.Simultaneously,bulk modulus,shear modulus,modulus of elasticity,and Cauchy pressure increased of the 2wt% hBN modified cellulose model by 11.2%,68.5%,58.7%,and 224.6%,while the polarizability decreased by 63.4%.While excessive content of nanoparticles can cause aggregation within the cellulose,resulting in performance degradation.The tensile strength,elongation at break,thermal conductivity,dielectric constant,dielectric loss,and power frequency breakdown field strength of different cellulose insulating paper were tested.It was found that the mechanical properties,thermal stability,and electrical properties of the cellulose insulating paper modified with h-BN were significantly higher than those of the unmodified cellulose insulating paper,and the modification effect of 2wt% h-BN was the best,which is consistent with molecular dynamics simulation results.(2)The thermal stability,mechanical properties,and electrical properties of cellulose modified by different silane coupling agents grafted with h-BN nanoparticles were significantly improved,and KH550 grafted with h-BN poccesses the best modification effect.The simulation results demonstrate that h-BN grafted with silane coupling agent can significantly increase the cohesive energy density,thermal conductivity,and glass transition temperature of the cellulose model,and reduce the mean square displacement and free volume fraction.At the same time,silane coupling agent grafted h-BN can significantly improve the toughness,deformation resistance,and dielectric properties of the cellulose model,and its modification effect is more significant than h-BN.Specifically,the Cauchy pressure increases by 204% compared to pure cellulose,and the polarizability decreases by 65.3%.The ability of three silane coupling agents to graft h-BN to modify cellulose models meets the following requirements: KH550 > KH570 > KH560.The experimental results indicate that the cellulose insulating paper modified by silane coupling agent grafted with h-BN poccesses better thermal stability,mechanical properties and electrical properties,and KH550 is the best surface modifier.(3)The thermal aging resistance of 2wt% KH550-h BN modified cellulose insulating paper is better than that of unmodified cellulose insulating paper.The doping of KH550-h BN can effectively inhibit the degradation of cellulose insulating paper.During the aging process,with the increase of aging time,the mechanical properties of modified cellulose insulating paper decrease more slowly than that of unmodified cellulose insulating paper.According to the thermal conductivity tests of the two types of insulating paper,the addition of KH550-h BN allows cellulose insulating paper to maintain a high heat dissipation performance.During the aging process,the thermal conductivity of modified cellulose insulating paper is always significantly higher than that of unmodified cellulose insulating paper.This is because the addition of KH550-h BN makes the internal h-BN cellulose chain network of the insulating paper more tightly connected and not easy to break,thereby maintaining a relatively stable thermal conductivity.According to the dielectric properties and power frequency breakdown field strength tests of the two types of insulating paper,the dielectric constant and dielectric loss of modified cellulose insulating paper are always lower than those of unmodified cellulose insulating paper during the aging process.After aging,the power frequency breakdown field strength of modified cellulose insulating paper decreased by 23.4%,while that of unmodified insulating paper decreased by 29.5%.This indicates that the doping of KH550-h BN inhibits the electrical performance degradation of insulating paper during aging.