Study On Preparation And Properties Of Dielectrics And Thermal Conductivity Of Ferroferric Oxide Nanoparticle Monodispersed Vegetable Insulating Oils

Nano technology provides an effective way to improve the insulation performance. Adding nanoparticle into the mineral insulating oil can improve the insulation properties and thermal conductivity of mineral oil. Vegetable insulating oil is considered as a kind of green liquid dielectric of high ignition point and natural degradation, which been widely used in distribution transformer. Studying of vegetable oil-based nanofluids and its application, are the research expansion of nano liquid dielectric researchThe shortcomings of nano vegetable insulating oil study mainly exist in the following aspects:(1) simulation of transformer internal environment, study of the stability of nanofluids in electrical, magnetic and thermal field(2) the influence mechanism of the physical and chemical properties of nanoparticles to the breakdown and dielectric properties of vegetable oil-based nanofluids. Based on the above two points, this paper preparation nanofluid with long-term stability, analysis the mechanism influence on the dielectric property and thermal conductive of nanofluids. The main research contents are as follows:(1)The monodispersed ferroferric oxide nanoparticles are prepared by high temperature decomposition method. The bonding situation of surfactant and nanoparticle was analyzed. The stability of nanofluids with different sized、prepared method and fiber exiting was studied. The results show the oleic acid surfactant closely combined with nanoparticle by covalent bond. When the vegetable oil-based nanofluids contain impurities such as paper fibers, the nanofluids still have good dispersion stability.(2)The influences of the size of Fe3O4 nanoparticles on the insulation properties of the nano vegetable insulating oil and impregnated paper have been studied. The dielectric constant、volume resistivity、dielectric loss factor、space charge density and ion mobility of different sized nanofluids have been tested. The resuts show that the larger size will be beneficial to improve the breakdown voltage and inhibit the space charge accumulation of nanofluids and impregnated paper.(3)The trap depths of Fe3O4 nanoparticle of different sized vegetable insulating oil were measured using thermal stimulated current method. The trap depths of nanoparticle of different sized insulating oil were verified using nanoparticles polarization model. The results showed that the predictive value of the nanoparticles polarization model is greater than the measured values of the model. A new physical model based on the surfactant polarization is proposed to explain the change rules of the trap depths of the nanoparticles of different particle sized and surfactant thickness. The results show good consistency compared the calculated results of the model with experimental measurement values.(4)The thermal conductivity of nanoparticle insulation oil of different sized and surfactant thickness has been measured using instantaneous line method. Compared Maxwell model, H&C model and Yu model with the measured values, it is found that these models cannot accurately predict the thermal conductivity of nano insulation oil. Analyze the influence of nanoparticles size, the thickness of surfactant, nanoparticle adsorption layer, on the thermal conductivity of nanoparticle insulation oil, and proposed a new model to explain the thermal conductive change of nanofluids. The results show that the model can exactly reflect the change rules of the thermal conductivity of nanofluids.The above research work provides the experimental basis and theoretical support provide for the preparation of the vegetable oil-based nanofluids of excellent electrical properties, long-term dispersion stability which has important reference value for practical application of the vegetable oil-based nanofluids into power transformer.