Electrical And Thermal Stability Of Mineral Insulating Oil Modified By APTES/SiO₂ Nanoparticles

Transformer is the core power equipment of power grid operation,and mineral oil is widely used as liquid insulation.With the implementation of China's Rural Revitalization Strategy,the development of rural power grid plays an important role in the development and improvement of rural agriculture.In recent years,with the continuous upgrading of rural power grid and the increasing load of power grid,higher requirements are put forward for the insulation level of power equipment such as transformer.Therfore,it is of great practical significance to modify mineral oil and improve its electrical and thermal stability for further promoting its application in high voltage field.Drawing lessons from the successful application of nano modification technology in other fields,this paper uses nano-SiO₂ to modify mineral oil to improve the electrical performance of mineral insulating oil.Surface modifier was used to improve the dispersion stability of nano-SiO₂ insulating oil,and the influence of electrical and thermal stability of modified insulating oil was deeply explored,as well as the mechanism of performance influence.In this paper,Aminopropyltriethoxysilane(APTES)surface modified nano-SiO₂ insulating oil was prepared by ultrasonic dispersion method,and the alternating voltage(AC)breakdown voltage,dielectric dissipation factor and volume resistivity under different SiO₂ concentration were measured.The influence mechanism of nano-SiO₂ modified insulating oil on breakdown performance was explored by first principles calculation based on density functional theory(DFT).In order to explore the thermal stability of APTES surface modified nano-SiO₂ insulating oil,the accelerated thermal aging experiment of oil-paper insulation samples was carried out,and the effect of nano-SiO₂ modification on the diffusion behavior of formic acid in the insulating oil-paper system was studied by molecular dynamics simulation.(1)It was observed by transmission electron microscope that APTES surface modification can effectively improve the agglomeration of nano-SiO₂,and the transmission coefficient of nano-SiO₂ insulating oil modified by APTES surface can reach the stable value quickly,which further shows that the surface modification of nano-SiO₂ can effectively increase the dispersion stability of nano-SiO₂ in oil.(2)By adding nano-SiO₂ modified by APTES in a certain concentration range,the breakdown voltage and volume resistivity of insulating oil can be increased.The breakdown voltage of APTES surface modified nano-SiO₂ insulating oil was significantly higher than that of pure oil by 28.0%at the concentration of 0.03 g/L.Although the dielectric dissipation factor was higher than that of pure mineral oil,the volume resistivity of APTES surface modified nano-SiO₂ insulating oil at this concentration was larger and the electrical performance was relatively optimal.The improvement of breakdown performance of insulating oil by APTES modified nano-SiO₂ is related to the interface between nano-SiO₂ and oil molecules.The interaction energy between APTES modified nano-SiO₂and alkane is higher than that of unmodified nano-SiO₂,and APTES also contain amino groups with higher positive potential,which can capture more free electrons.Therefore,when electrons are introduced into the interface,more electrons are distributed on the APTES modified nano-SiO₂,which indicates that the interface between APTES modified nano-SiO₂ and alkane can capture more free electrons in the oil and delay the development of the breakdown channel in insulating oil,thus explaining that surface modification by APTES has a good effect on improving the AC breakdown voltage of mano-SiO₂ modified insulating oil.(3)The addition of nano-SiO₂ modified by APTES can effectively delay the thermal aging rate of insulating oil and increase the thermal stability of insulating oil.The results show that with the aging time,the acid value and dielectric dissipation factor of nano-SiO₂ insulating oil-paper samples modified by APTES are smaller,the morphology of insulating paper is more complete,and the insulating paper has better thermal stability.In order to further explore the influence of APTES surface modified nano-SiO₂ on the aging products such as formic acid in insulating oil,molecular dynamics simulation was carried out on the diffusion motion of formic acid.The results showed the binding effect of nano-SiO₂ modified by APTES to formic acid molecules weaken the diffusion of formic acid,especially reduce the damage of formic acid to the internal hydrogen bond structure of cellulose insulation paper,thus reducing the harm of formic acid to the oil-paper insulation system.