Study On Preparation And Electrical Properties Of BN/Nanocellulose Modified Vegetable Insulating Oil

With the popularization of vegetable insulating oil as a new environmental-friendly dielectric liquid in transformers,higher requirements are put forward for the electrical and physical and chemical properties of vegetable insulating oil.Nano-modification technology can effectively improve the properties of vegetable insulating oil,so it has become the focus of research on nature ester insulating oil.At present,the nano-modification of vegetable insulating oil still faces many problems,mainly as follows:(1)Vegetable insulating oil has the disadvantage of poor heat dissipation because of its high viscosity and low thermal conductivity.How to choose reasonable nano-modification methods?(2)At present,nano-modified vegetable oils has poor dispersion stability,and the phenomenon of agglomeration exists in long-term use,which may cause the breakdown voltage to decrease and affect the effect of nanomodifying.(3)Study on the influence of nanoparticles on electrical,thermal properties and aging properties of modified insulating oil and its mechanism.Based on the above three problems,BN/CNF modified vegetable insulation oil was prepared by using boron nitride(BN)as modified particles and nanocellulose(CNF)as additive.Thermal and electrical properties were tested,thermal stability was studied and the influence mechanisms were analyzed.The main contents of this paper are as follows.(1)CNF with good dispersion in oil was prepared by surface modification.Flake BN nanoparticles were prepared by ultrasonic peeling.The prepared Nano-Additives were characterized by scanning electron microscopy,X-ray diffraction and infrared spectroscopy.The dispersion stability of the prepared nano-insulating oil was analyzed by spectrophotometry and Zeta potential method.The effects of CNF on dielectric properties and thermal conductivity of vegetable insulating oil were studied.The results show that CNF can effectively adsorb BN nanoparticles in the prepared nano-insulating oil so the modified oil has good dispersion stability.The dielectric properties and thermal conductivity of vegetable insulating oil are not significantly affected by a small amount of CNF.(2)The dielectric properties and thermal conductivity of BN/CNF modified vegetable insulating oil were studied.Electrical conductivity and dielectric loss factor of BN/CNF modified vegetable insulating oil decreased by 58.5% and 42% respectively by adding nanoparticles with 0.2% concentration.The thermal conductivity test shows that adding BN/CNF can enhance the thermal conductivity,and the thermal conductivity increases by 14.3% at 0.2% BN content.The heat transfer experiment shows that BN/CNF can effectively improve the temperature uniformity of insulating oil and enhance the thermal diffusion efficiency under the applied electric field.The thermal conductivity formula of nanofluids based on Fourier equation and Brownian motion is obtained considering the flake structure of BN and the contribution of Brownian motion.The calculated results are in good agreement with the experimental data.(3)The thermal aging experiment of BN/CNF nano-vegetable insulating oil was carried out.The results show that BN/CNF modification can effectively slow down aging of insulating oil.The stability of the modified oil was analyzed by thermogravimetric test,acid value test and moisture test.Results show that the addition of BN nanoparticles can improve the thermal stability of insulating oil and delay the pyrolysis of insulating oil.At the same time,CNF can absorb moisture in insulating oil and delay the generation of acid products.Therefore,BN/CNF added in oil has formed a joint effect to slow down the aging of vegetable insulating oil.