Investigation On The Trap Characteristics Of Oil-paper Insulation

With the rapid development of China's economy,electricity demand increased year by year,but the energy centers and Electricity load centers are mostly far away in China.In recent years,in order to satisfy the economic development and social progress on the demand for electricity,China vigorously develop UHV transmission project.In "Thirteen Five" period,the State Grid Corporation plans to build total of 23 UHV transmission project.By 2020,China will build total of 27 UHV transmission lines.By then,China will hold the largest and longest UHV transmission lines all over the world.In the UHV transmission lines,many of the power equipment that use the traditional insulation materials and insulation structure are facing many new problems.Among them,the space charge is an urgent problem to be solved.Space charge movement will seriously affect the dielectric properties of oil-paper insulation and accelerate the aging of insulating materials,even cause insulation breakdown or damage the electrical equipment.And the trap as the main structure of the storage space charge has an important impact of space charge accumulation,transportation and dissipation.Therefore,A Study on trap characteristics of oil-paper insulating is very important to understand the development of space charge and improve the insulation characteristics.As we all know,oil paper insulation medium can be as high molecular polymer.On the basis of fully understanding the physical and chemical properties of polymer materials,this paper comprehensively considered the main problems of oil paper insulation under the actual working conditions.Based on the energy band theory and thermal stimulation method,the trap characteristics of oil paper insulation were studied systematically by using the isothermal discharge current measurement system constructed voluntarily.A series of accelerated thermal aging and AC/DC composite electrical aging tests were carried out on oil paper insulation.Then,to obtain the trap information of the oil paper insulation medium with different thermal aging degree and electrical aging degree of different AC/DC composite ratio through the isothermal discharge current method.In the case of the cellulose model with defects,the internal trap characteristic information was simulated by taking advantage of the molecular simulation software(Material Studio)relying on molecular dynamics and the density functional theory of computational quantum chemistry.The main achievements of this thesis are as follows: For the oil and paper insulation with different thermal aging degree,the trap energy density increases with the aging time,and the trap level gradually deepens;For the oil and paper insulation under the composite voltage of AC / DC composite voltage,the internal trap energy density increases with the aging time.When the aging time is the same and the composite voltage is 50%,the trap energy density of the oil-paper insulation is the largest,the trap energy density increases but trap level is gradually reduced with the increasing of the AC voltage.Eight different kinds of insulating paper cellulose defects models were constructed by molecular simulation technique.The depth of trap level of different cellulose models was calculated according to the electron affinity.It was suggested to protect the No.6 hydrogen bond to improve the capability of oil and paper insulation.