| As a key overvoltage protection device in high-voltage and ultra-high-voltage DC transmission systems,the performance of DC bus arresters directly affects the operation safety of the whole power system.Due to withstanding working voltage long term and overvoltage occasionally in service process,there is partial aging degradation phenomenon in the valve plate column,the core structure of lightning arrester,which change the electric and thermal field distribution inside the arrester;cause the focus of local field;accelerate the electric or thermal breakdown risk of the arrester,and directly affect the safe and efficient operation of the grid.Firstly,according to the Standards of GB11032-2000/IEC60099-4,a program controlled Muffle furnace was used to build the equivalent accelerated aging test platform for ZnO resistors in this thesis,and accelerated aging tests for the ZnO resistors were done for different time.According to the test results,the change law of the insulation resistance of ZnO resistors was summarized.Secondly,according to the actual size of the DC bus arrester with single section and double column in parallel,the three-dimensional geometric model was established.Based on electric field theory and heat transfer theory,a mathematical model of finite element for simulation was established.Using the steady state solver of finite element analysis software,the electric field,thermal field and voltage bearing rate of arrester under DC voltage are numerically solved.Based on the steady-state numerical solution,the transient solver was superimposed to solve the potential and voltage bearing rate of the lightning arrester with high frequency,and the general rule of the potential and voltage bearing rate variation after local aging at different positions of the valve column was summarized.Finally,a new heat dissipation structure of zinc oxide arrester was proposed based on the simulation results of DC and high frequency field.Three-dimensional geometric models of traditional and new structure arresters were established respectively,and numerical solutions were carried out by using finite element simulation software,and the corresponding temperature distribution law and temperature rise rate were compared and analyzed.The influence of structural factors such as the number of heat dissipation channels,diameters,and heat dissipation medium on the temperature rise of the arrester was systematically analyzed,and an optimized structure scheme to reduce the maximum temperature rise of the arrester was proposed.The simulations of local aging of zinc oxide arrester on the distribution of electric field,thermal field and voltage bearing rate in DC steady state and high frequency transient state were carried out in this thesis.The proposal of the design scheme of the heat dissipation structure of the arrester provides the theoretical basis and data support for the body design,installation,operation and maintenance of the DC arrester.It has an important reference for the design and development of zinc oxide arrester products. |
