Cooling System Design And Calculation Analysis Of MOA Based On Boiling Heat Transfer Technology

Due to the rapid development of electric power industry utility, the increase of power system capacity in our country results in evidently large short-circuit current, and thus limiting short-circuit current has become an important measure to ensure the safety of power grid. Series resonance FCL (fault current limiter) based on MOA(Metal Oxide Arrester, MOA), which is widely used in the grid, is a very effective device in current limitation, but its security in operation is affected because of the limitation of thermal stability requirements of the ZnO varistor. Therefore, the research on cooling system of MOA is of essential importance for improving the operation stability.According to the principle that large quantities of latent heat can be absorbed in the liquid boiling, the MOA cooling system has been proposed based on boiling heat transfer technology. This system may improve both the cooling conditions of the MOA and the safety and reliability of FCL in the power grid. The main work of this paper include:the establishment of the mathematical model of MOA with the use of finite element analysis software and the calculation of the temperature distribution of MOA according to the boiling heat transfer theory. The specific works performed in this paper are as follows.Firstly, the process of generation, growing up, and breaking away of vapor bubble and the related theory are described, the factors of influencing this process are analyzed, and the stages and characteristics of boiling occurring in a large container are discussed.Secondly, the simulation model of the MOA temperature field are developed based on the actual structure and dimensions of MOA, the basic assumptions on computation domain and boundary conditions are given, and the approximation of internal heat source is proposed. In order to get the loading conditions of MOA in temperature field calculation, the relationship between heat flux and wall superheat of MOA’s different cooling surfaces is determined by using the formula of heat flux in different pool boiling stages under the selected cooling medium.Thirdly, several analysis methods of the MOA temperature field are introduced, especially the method and steps of using ANSYS finite element analysis software. The calculation procedure and program flow chart for solving the difficult problems involved in this paper are presented. These difficult problems include the large calculation model, the poor convergence of nonlinear solution, the long calculation time, and the huge calculation amount.Finally, the temperature field distributions of MOA are obtained by the use of the ANSYS software, and based on the calculated results, the cooling effect by using traditional cooling method is compared with that by using boiling heat transfer technology. In addition, the heat transfer characteristics and the factors of influencing the heat transfer for the different heat transfer surfaces of MOA are analyzed, and the heat transfer capacities of the structure of MOA with different cooling channel diameters are compared.