The Effect Mechanism Of Titanium Dioxide Nanoparticles On The Creeping Streamer At The Surface Of Oil-Impregnated Pressboards

Power transformer is one of the most important and critical power equipment in the power transmission and distribution system.The oil-paper composite medium is the main insulating medium inside the transformer,and its insulation performance directly affects the safety and reliability of the entire power system.It is found that using TiO2 nanoparticle can not only increase positive lightning impulsive breakdown strength of transformer oil,but also both of positive and negative lightning impulsive creeping flashover voltages of oil-impregnated pressboards.Possible modification mechanisms have been proposed to explain the enhanced insulating performances of nanofluids.But there is still lack of a theory to explain the effects of nanoparticles on creeping flashover characteristics of oil/pressboards.Firstly,the creeping streamer on the TiO2 nano-modified transformer oil-impregnated pressboard was the research object,and spherical TiO2 nanoparticles with a radius of 10nm were prepared by wet chemical method,and the transformer oil and the oil-impregnated pressboard were modified by the nanoparticles.To study the creeping flashover voltage and creeping streamer development characteristics of nano-oil-impregnated pressboard and pure oil-impregnated pressboard firstly,a streamer shadowgraph measurement system was established.The result show that nanoparticles can increase creeping flashover voltage of nanooil-impregnated pressboard,prolong the creeping flashover time,reduce the development length of the streamer at the interface and restrain the development speed of the streamer.And the board interface at the streamer branch is thicker,showing a more spread to the oil phenomenon.Secondly,the trap and space charge characteristics of nano-oil-impregnated pressboard and pure oil-impregnated pressboard were studied,and the relationship between the trap and charge characteristics of nano-modified paperboard was explored.The results show that the surface charge density is 0.44778μC/m2,which is only 11%of pure oil-impregnated pressboard,and its thermal stimulation current peak value of nano-oil-impregnated pressboard reach 31.2pA,which is 2.84 higher than that before modification,and its.TiO2 nanoparticles introduced a large number of polarizations and traps in the transformer oil-paper insulation system,which changed the charge transport characteristics of the oil-impregnated pressboard interface.Finally,combined with the surface charge transport characteristics,as well as the trap characteristics of oil/pressboard,a possible modification mechanism was proposed to explain the restrained propagation of creeping streamers on the surface of nano-modified oil/pressboard.The additional polarization of TiO2 nanoparticles decreases the permittivity difference between oil and pressboard.It decreases the electrostatic attractive force to creeping streamers.The squeezing effect of creeping streamer is alleviated,resulting in a stronger shielding effect and decelerated propagation of creeping streamers at nanofluid/pressboard interface.As a result,the interfacial insulating properties of oil/pressboard is improved.Besides,the ionized charges can be dissipated quicker by trapping and detrapping process in these shallower traps avoiding the accumulation of charges on the interface of oil/pressboard.The distortion of interfacial electrical field is then alleviated,which leads to the restrained propagation of creeping streamer at the surface of oil/pressboard.