Study On An HTS Conductor With Quasi-isotropic And High Engineering Current Density And Its Performance

With the development of superconducting technology,significant progress has been made on performance and preparation process of second generation(2G)temperature superconducting(HTS)wire,and achieved large-scale commercial production.2G HTS wire has advantages of low loss and high current-carrying as well as excellent mechanical characteristics.However,the single superconducting wire has limited current-carrying capacity,and multiple connected in parallel is inevitable.Superconducting conductors of different layouts have been proposed internationally based on the 2G HTS wire,such as Conductor on round core(CORC),Twisted Stacked-Tape Cables(TSTC)and Quasi-Isotropic strand(Q-IS).An HTS conductor with quasi-isotropic and high engineering current density is proposed.The HTS conductor consists of inner quasi-isotropic strand and outer HTS power cable layers similar with the conventional HTS cable ones.That is.the HTS conductor is a power cable with replacing the copper former by a twisted quasi-isotropic strand.The HTS conductor can greatly increase the engineering current density by choosing appropriate twisting pitch of inner Q-IS and winding pitch of outer power cable layer.It has advantages of high engineering critical current density and mechanical flexibility as well as quasi-isotropic critical current density.This thesis also describes the fabrication process of new conductor and focuses on the twisting method of Q-IS and the fabrication of copper terminals.Studying the dependence of critical engineering current density of the new conductor on twisting pitch of inner Q-IS,winding pitch of the outer HTS power cable layer and the number of power cable layers by numerical simulation.A model for calculating the magnetic field distribution of twisted Q-IS is suggested,the magnetic field distribution of twisted Q-IS can be calculated quickly and accurately based on this model.The relationship between the critical engineering current density of the proposed conductor and the twisting pitch of the Q-IS and the twisting pitch of the HTS power cable layer is experimentally studied,and the correctness of the numerical simulation is also venfied.The main factors limiting the increase of the critical engineering current density of the new conductor are also obtained.The current transfer length(CTL)of the new conductor was analyzed and measured by experiment.By using circuit model to simulate the transfer process of current in the layers of superconducting tape,and a novel numerical method of calculating CTL in 2G HTS wire considering multi-layers is proposed.The accuracy of the method is also verified by experiments.