Study On Electrical And Electrical Aging Characteristics Of Nano-TiO₂ Modified Insulating Paperboard

The power transformer is the core equipment of energy conversion and transmission in the power grid,and it is the key node for the safe and stable operation of the power system.The properties of the cellulose paper/pressboard directly affect the reliability of transformer main insulation,and the aging of the cellulose paper/pressboard is also the dominating factor for the main insulation failure of the power equipment.Since the cellulose paper/pressboard is irreplaceable in transformer operation,the properties of cellulose paper/pressboard directly determine the safety of oil-immersed transformer operation.Therefore,it is of great application value to carry out nanometer modification technology to improve the performances of cellulose paper/pressboard to guarantee the reliability of transformer insulation system.In this paper,the preparation of different diameters?5 nm,10 nm,20 nm and 30 nm?with different mass fractions?1%,3%,5%and 7%?TiO₂-modified cellulose pressboards were conducted in the laboratory.The relevant physical,electrical,and charge trap characteristics of cellulose pressboards before and after electric aging were studied to explore the influence mechanisms of nano-TiO₂ particles on the performance of cellulose pressboards.The main research contents and results of this paper are as follows:?1?The dielectric response method was used to collect the frequency domain dielectric parameters of the modified pressboards.The electrical insulating strength test was carried out to explore the influences of nano-TiO₂ diameter and mass fraction on the partial discharge?PD?and breakdown of the pressboards and obtain the breakdown characteristics of the modified pressboards at different temperatures.The results show that the nano-TiO₂ addition of 5%mass fraction and 10 nm diameters significantly improve the electrical performance and the surface structural of cellulose pressboards,and it effectively restrain the accumulation of surface charge on pressboard'surface.?2?Accelerated electric aging?0 h,10 h,20 h,30 h and 40 h?was carried out under DC 8kV voltage at room temperature.The physical,dielectric,partial discharge and breakdown characteristics of the modified pressboards were tested before and after electric aging.The test results represent that the process of electric aging leads to the decrease of the degree of polymerization?PD?and the increase of the moisture content of the cellulose pressboards,and it decreases of the dielectric,partial discharge and breakdown performance of the cellulose pressboards.The nano-addition of 5%mass fraction works well on the aged samples and enhances the electric properties of cellulose pressboards.?3?Electric aging aggravates the surface charge accumulation degree of the cellulose pressboards.The surface charge decay rate of aged samples are lower than un-aged ones in preliminary decay stage,while they are higher than the aged ones in middle and later decay periods.The addition of nano-TiO₂ with 5%mass fractions significantly restrains the accumulation of surface charge on aged samples.Electrical aging will damage the surface structure of cellulose pressboard,shorter the cellulose chain,increase the traps densities and promote the conversion of the shallow traps to the deep ones.The addition of nano-TiO₂ with a certain mass fraction?1%⁵%?improves pressboard'surface structure and effectively reduces the number of traps to restrain the electric aging process of the cellulose pressboards.