AC Loss Analysis Of The Quasi-Isotropic Conductor

The second-generation(2G)high-temperature superconducting(HTS)coated conductor(CC)with multilayer-composited structure has the characteristics of high current-carrying capacity,high aspect ratio,anisotropy and so on.The quasi-isotropic conductor stacked by 2G HTS CCs has a centrosymmetric structure with advantages of high engineering current density,good mechanical properties and low AC loss.The quasi-isotropic conductor will have great application prospects in the manufacture of high-field magnets,large-scale busbars and high-current transmission cables and other electric power equipment.However,AC loss generated during the operation of the quasi-isotropic conductor will heavy the refrigeration burden,increase the cost and affect the stability of the system.Therefore,accurate assessment of AC loss in the quasi-isotropic conductor under different working conditions is one of the most important topics in the application of superconductivity.This thesis introduces the mechanism of AC loss in HTS conductor,the development of numerical calculation and the relating experimental measurement methods in detail.And on the bases of simulation calculation and experimental measurement,AC loss of quasi-isotropic conductor is discussed and a reduction method is studied.Mainly included as follows:Two main numerical methods for calculating AC loss of HTS conductors are introduced,which are H formulation and T-A formulation.The constraint equations,calculation principles,advantages and disadvantages of the two formulations are discussed in detail.And then,the magnetic flux pinning process of the HTS conductor which causes AC loss is simulated and explained.Aiming at AC loss caused by the quasi-isotropic conductor transmitting alternating current(AC).This paper has made an experimental setup to measure the critical current and AC loss of the conductor.A three-dimensional T-A simulation model of the quasi-isotropic conductor has also been built.The T-A formulation calculates the AC loss,current density distribution and magnetic field distribution of the conductor which are basically consistent with the experimental results.On the basis of simulation results,we have customized the twisting apparatus and explore the relationship between AC loss and the twisting quasi-isouopic conductor.Finding a way to reduce AC loss of the quasi-isotropic conductor.When the quasi-isotropic conductor carrying direct current(DC)under an external AC magnetic field,the generated magnetization loss,dynamic loss and total loss are measured by experimental setup.Two-dimensional T-A simulation model is also built to calculate total AC loss of the entire strand.The simulation and experimental results are consistent.The comparisons between magnetization loss and dynamic loss under different DC transmission current,external AC magnetic field and frequency are studied.This thesis provides a method for evaluating and calculating AC loss of the quasi-isotropic conductor.What’s more,it also provides a reference for the selection of the refrigeration power of the cooling system.The results of this study can be an important reference for AC loss analysis of the 2G HTS conductors with other different structures.