| The second-generation(2G)high-temperature superconducting(HTS)coated conductor(CC)nowadays can be commercially manufactured in km-level,and is equipped with the characteristics of high current-carrying capacity and excellent mechanical strength.To meet the needs of high current-transporting capacity,there is a novel arrangement for 2G HTS CCs,which is called quasi-isotropic conductor where 2G HTS CCs are symmetrically stacked.Due to its high engineering current density,compact structure and lower anisotropic characteristics,wide application in high-field magnets has been applied for the quasi-isotropic conductor.However,AC loss occurs in the quasi-isotropic conductors when carrying AC current or under AC magnetic field,which will decrease the efficiency of cooling system and the stability of superconductors.Therefore,it is essential to accurately calculate AC loss for further applications of superconductors.This thesis introduces the mechanism of AC loss in HTS conductors and the associated analytical formulations for estimating AC loss.Moreover,to accurately calculate the critical current of the quasi-isotropic conductor,the self-consistent model is proposed to predict the critical current of the quasi-isotropic conductor at various temperatures for the first time,providing solid support for application and experimental verification of the quasi-isotropic conductor.Based on the theory of numerical modelling method,2D model using T-A formulation has been constructed to simulate AC loss of the quasi-isotropic conductor at various temperatures.The main contents are listed as follows:Aiming at AC loss caused by the quasi-isotropic conductor transmitting alternating current(AC).This paper has built a two-dimensional T-A simulation model of the quasi-isotropic conductor at various temperatures.The dependence of normalized critical current and frequency on AC loss has be investigated and the according critical current density and magnetic field distributions have been presented for further explanations of AC loss characteristics of the quasi-isotropic conductor.In terms of AC loss when either exposed to AC magnetic field or simultaneously carrying AC current and exposed to AC magnetic field of the quasi-isotropic conductor,magnetization loss and total loss(consists of magnetization loss and transport loss)has been obtained based on two-dimensional T-A simulation model.The dependence of the amplitude of the external magnetic field and the normalized critical current on AC loss has been studied as well.From the simulation results of the quasi-isotropic conductor at various temperatures,the cooling efficiency of the quasi-isotropic conductor at temperatures has been provided with solid support,and the optimum operating temperature has been established as well. |
