Analysis Of Cooling Medium Flow Characteristics And Magnetic Field Distribution Of High Temperature Superconducting DC Cable

High-temperature superconducting direct current transmission technology has the advantages of large transmission capacity,small volume,lightweight and small line loss,and has become one of the important technical choices for long-distance DC power transmission.In this thesis,the current and temperature distribution of superconducting DC cables with different structures under overcurrent conditions and the magnetic field distribution under normal operating conditions are simulated,the selection of cable structure is analyzed,and the flow characteristics of the superconducting cable cooling medium in the bellows are simulated and analyzed.In this thesis,the superconducting DC cable in the state of over current is firstly studied.The resistance model of the cable body is established in MATLAB and the steady heat transfer model is built in COMSOL.The joint simulation of two models is realized through the program call,and the current distribution of each layer of single-channel and double-channel superconducting cables under fault current is simulated.Using the current distribution data to calculate the heat generation rate of each layer and writing it into the fluid-solid conjugate heat transfer transient model.The temperature distribution of cable which obtained from the simulation is analyzed.The influence of the cable copper skeleton radius and the cooling medium flow rate on the maximum temperature of the superconducting layer of the cable is studied.Based on the simulation of fluid mechanics,the k-co liquid nitrogen turbulence model is established in COMSOL.The distribution of the velocity component,pressure and turbulent kinetic energy of liquid nitrogen in the flow channel is analyzed.Using the turbulence model,the effects of some parameters such as geometrical dimensions and flow velocities of the bellows on the inlet and outlet pressure difference is calculated.The influence of parameters such as wave height,wave pitch and flow velocity on the outlet temperature was calculated by using the steady state turbulent heat transfer model.Comparison of the difference of inlet pressure and outlet temperature between corrugated pipe and smooth pipe is discussed.Finally,a two-dimensional model of unidirectional and bidirectional superconducting DC cables is established,and the magnetic field distribution of superconducting cables under different structures is simulated.Combined with the anisotropy of the superconducting tape and the magnetic field distribution of the superconducting tape,the critical current of the superconducting cable is simulated and a short sample of the superconducting cable is wound,which is compared with the simulation results.