Electromagnetic Analysis And Design Of High Temperature Superconducting Tapes

High-temperature superconductors (HTS) possess a number of unique properties that make them attractive for use in many engineering applications, ranging from power cables to transformers. To optimize the design of a superconducting system, it is necessary to predict the electromagnetic behavior of the superconductor under different current conditions. Meanwhile, the only available HTS conductor for a practical application seems now to be Bi2223/Ag HTS tape. So, we have started a research on the electromagnetic characteristics of Bi2223/Ag HTS tapes in liquid nitrogen under self-magnetic field. The research mainly contains three parts as follows:1). We have carried out an experimental and numerical study on the electrical behavior of HTS tape under the over-critical current. In the experiment, we measured the voltage-current curves for the region from 104 A to 556 A (60Hz). In the simulation using the heat transfer and Finite Difference Method, the electrical and quench properties of HTS tapes under these fault currents were calculated. The simulation results resembled experimental results. From the analysis, 3 matters were investigated. Firstly, to understand the electrical behavior in detail, we investigated the current sharing between the superconductor and the metal sheath in Bi-2223/Ag tape applying the equivalent equations. Secondly, we confirmed the relationship between the resistance and temperature generated by the over-critical current numerically. Finally, Through analyzing normal resistance voltage developing and recovery characteristics of HTS tapes under different over-currents, quench development under different cooling conditions was analyzed as a function of the amplitude and duration of the applied currents. As a result, we could find the optimal operating condition considering the protection of the HTS tape against the alternating over-current.2). We have accomplished an experimental and numerical study on the transient electromagnetic behavior of HTS tape under the pulse current. In the experiment, the pulse current with different frequency (50Hz-4500Hz) was increased rapidly from a small steady state level to a larger level higher than the critical current. In the simulation, A Finite Element Modeling method was proposed to analyze the transient phenomena. The E ? J constitutive law together with an H-formulation was used to calculate the current distribution and electromagnetic fields in HTS tape. The simulation results agree well with the experimental ones. From the analysis, 3 matters were investigated. Firstly, the voltage-current relation shows that HTS tape has a good superconducting-to-normal conducting recovery characteristic under pulsed current with high frequency. Secondly, we determined the repartition of current between the superconducting material and the silver sheath, in particular in the high current range. Finally, to understand the responds of HTS tape under the pulse current in detail, we plotted the current density and magnetic distribution both above and below critical current in the tape considering the anisotropy.3) We have presented numerical results on DC current carrying capability and AC transport current losses of the large-current conductor assembled from multifilament Bi2223/Ag tapes. From the analysis, 2 matters were investigated. Firstly, the DC critical current of large-current conductors lies systematically below the sum of critical currents of the tapes. Secondly, an empirical description based on the Norris model is derived to estimate the AC self field transport current losses.