Properties Of Thermal Conductivity And Insulation Of Vegetable Insulating Oil Based BN Nanofluids

Nanotechnology is widely used in improving the thermal conductivity and insulation properties of materials.Vegetable insulating oil,as dielectric liquid,with high flash point and biodegradable nature,has been widely applied in power distribution transformers.The development of nano vegetable insulating oil is not only an extension of the research and application,but also a new research topic in nano dielectrics.Currently,there still exist some problems in research direction of nano insulating oils including three key issues:?1?Whether the nanoparticles can give consideration to the insulation performance and also improve the heat dissipation performance of vegetable insulating oil.?2?The molecular structure of vegetable insulating oil is different from mineral oil,its dielectric conductivity,high dielectric loss,lack of study on the mechanism of the influence of nanoparticles on the electrical conductivity and dielectric loss factor problem.?3?The effect of nanoparticles'morphology on the streamer propagation of vegetable insulation oil.Based on the above three problems,different nanoparticles affecting the heat transfer performance of vegetable oil were researched and analyzed,the insulation properties of semi conductive nano materials on the dielectric properties of vegetable insulating oil were studied and development of streamer morphology were analyzed.?1?Preparation methods of insulating material BN nanosheets and oleic acid coated semi conductive Fe₃O₄ nanoparticles and their nano oils were studied.The characterization of nanoparticles was tested by various material characterization methods,and the reasons for the stabilization of nanofluids were analyzed.The experimental results show that the BN nanoscale and the oleic acid modified Fe₃O₄ nanoparticles have excellent dispersion stability.The thermal conductivity and electrical properties of the nano oil are tested.The results show the thermal conductivity of nanofluids increased by14%and the dielectric loss is reduced by 50%.?2?The thermal conductivity calculation model of nanofluids with different shapes were studied.Thermal conductivity using typical Maxwell model,H&C model and Yu model were calculated and it was that found several calculation models were far less accurate than the actual measured values.The factors of nano particle shape and thermal effect of insulating oil adsorption layer was analyzed,a new calculation model of the thermal conductivity of nanofluids is proposed,and the calculated value is in good agreement with the measured values.The dielectric loss model of BN and Fe₃O₄nanofluids were analyzed.Seeing electrophoretic migration analysis and ion conductance of nanoparticles and their effect on nanofluids'electrical conductivity two kinds of nanofluids electrical conductivity model and the dielectric loss factor mode were put forward.?3?The different streamer characteristics of nano vegetable oil are studied.By using high speed camera and optical platform to observe streamer initial,propagation and breakdown process of nanofluids under the positive and negative lightning impulse voltage were analyzed.The results show the nanoparticles increased the number of the main channel of a streamer,and reduce the stopping length of streamer.And there was secondary streamer at 100²00?s.Based on the theory of electric field space charge,the cause of secondary reverse streamers produced by nanoparticles were analyzed.?4?The surface discharge characteristics of different nano vegetable insulating oil paper are studied.The streamer development,dissipation and breakdown process under lightning impulse voltage were observed and analyzed.The results show the lateral branch of the nano oil-paper is obviously increased in the development process,and the streamer is dispersed after 30?s.At about 140?s,all samples generate secondary streamer in the dissipating process.Based on the interface charge theory,the effect of nanoparticles on the electric field in oil-paper insulation is analyzed,and reason of difference streamer shape in nano oil paper is revealed.Above research work,for the preparation of excellent electrical performance,low dielectric loss,considering the insulation performance to improve the dissipation performance of nanofluids provide experimental data and theoretical analysis.