Effects Of TiO₂ Nanoparticles Micro-characteristics On Ion And Electron Mobility In Transformer Oil

Due to the excellent thermal conductivity and insulation properties,transformer oil-based nanofluid has shown great potential to improve the dielectric strength of transformer oil.In response to the improvement of the properties,models such as "shallow traps" theory have been proposed to explain the nano-modification mechanism of the charge transfer properties and the higher breakdown strength in transformer oil-based nanofluid.Although the way of interpretation is different,the transfer characteristics of carriers such as electrons,ions or charged particles only proved indirectly by simulation or other concepts,but not directly proved by the experimental results.Our research group has carried out some basic work and experiments on ion and electron mobility in TiO2 transformer oil-based nanofluid.However,its experimental sample is single and its universality can not be proved.And the mechanism is not explained in depth.Therefore,to further explore the modification mechanism of transformer oil-based nanofluid in the microscopic point of view,our research carried out a large number of experiments on different particle sizes and shapes in deep analysis,.For the ion transport process,spherical particle sizes of 5 nm,10 nm,15nm,30nm and rod-shaped nanofluid were measured in the field of 5kV/m,25kV/m,50kV/m,150kV/m.The results show that the ion mobility of TiO2 transformer oil-based nanofluid is generally lower than that of pure oil.For the spherical nanofluid,the smaller the particle size,the lower the ion mobility.The ion mobility of rod-shaped nanofluid is similar to that of spherical 10nm nanofluid.Charged characteristics of nanoparticles affect the migration of charge carriers.By analyzing the electrical conductivity,average ion concentration and ionic equivalent radius of nanofluid and pure oil,the special ion migration rules of nanofluid were explained.For the electron transfer process,electron mobility of TiO2 transformer oil-based nanofluid is higher than that of pure oil.First,we prove the accuracy of the results by breakdown time delay method and then use the method to measure the electron mobility of pure oil and spherical 5nm,10nm and rod-shaped nanofluid.The electron mobility of these kinds of nanofluid is all higher than that of pure oil.And within these nanofluid,the electron mobility of spherical 5nm with smaller particle size is larger than the spherical lOnm nanofluid with larger particle size.The experimental results of rod-shaped and spherical 5nm nanofluid are similar.Based on the experimental results.the feasibility of the measurement results is further proved by calculating the relationship between the classical electron radius model and the electron-ion relationship.Combined with the unique water absorption characteristics and the "shallow traps" thoery.a mechanistic explanation of the electron mobility in TiO2 transformer oil-based nanofluid is formed.For the conductance process of nanofluid.a conductance current test platform was set up to measure the conductance current of nanofluid in the field of 0-5kV/mm and characterize by the I-E curve of Fowler-Nurdheim relationship.It is found that the conductance of TiO2 transformer oil-based nanofluid also has three stages of ohmic zone,tunneling zone and space current saturation zone.Compared with pure oil under the same measurement conditions,the addition of nano-particles will reduce the threshold field strength of the transformer oil to the corresponding stage in the same experimental conditions.