AC Losses Of High Temperature Superconducting Tapes And Coils

Because AC losses of high temperature superconducting (HTS) tapes and coils have direct affects on the stability of HTS apparatus, the investigation of AC losses of HTS tapes and coils has always been one of the most important research branches of HTS application.In this paper, the research progress of AC losses of high temperature superconductors and the existing problems on AC losses investigation are introduced; The characteristics of the critical current and AC losses of HTS tapes, stacked tapes and HTS coil, such as electro-magnetic characteristics, the anisotropy, the mechanics characteristics and the effects of insular layer between stacked tapes and the influence of frequency of AC transport current etc, are investigated. The main research aspects are as follows:The method of AC transport losses measurement in AC applied magnetic field was investigated. Upon the analysis of AC loss measurement, a method to measure AC transport losses in AC applied field was proposed by use of double '8' shape coils. A programme controlled system was set up to measure AC losses of HTS tapes and coils, which can ensure the experiment data needed by theoretical analysis and verification.Based on the effective mass theory and critical state model, an anisotropic theory of critical current and AC losses for single HTS tape and tape stacks were established. Analytical formulae were presented to calculate critical currents and AC losses with an arbitrary angle between the wide side of HTS tape and the direction of AC or DC applied fields. From the anisotropic theory of AC losses of HTS sample, a numerical model to calculate AC losses of HTS coil was developed. To verify this model, AC transport losses of a double winded pancake HTS coil were calculated and compared with the measured results.The critical current and AC losses in HTS tapes were measured under different winding radii and pulling stress. A theoretical model was proposed to describe the relationship of critical currents and AC losses with the winding or pulling stress-strain. It is shown that the calculated values were in agreement with the measured results quite well.To study the of effect of insulator layer among tapes in a stack and the influence offrequency of AC transport currents on AC losses, AC losses of a single tape and stacks were measured for AC transport current with different frequencies in two cases: with and without insulator among the tapes in a stack. Theoretical formulae to calculate hysteresis losses in stacked tapes were also presented.In addition, the characteristics of critical current of HTS tapes in AC applied field and that of voltage-current curve when transport AC currents were studied. The problem on the criterion of AC current carrying capacity of HTS tape was discussed, and some suggestion on the criterion of AC current carrying capacity were proposed.