A Study Of The Stability Of High Temperature Superconducting Coils

High temperature superconducting(HTS) material has superior properties of resistanceless in DC condition, high current density, high performance in magnetic field and so on. Thus, the HTS magnets, which is made from the HTS tapes, has been widely recognized. Important achievements of HTS magnets have been made in high field magnet, HTS motor and generator, fault current limiter, transformer, induction heater and so on. Part of them has been successfully commercialized. However, the stability of HTS magnets needs more research due to the lack the relative successful experience, because the quench properties of HTS material has significant difference with low temperature superconductors.In this study, the stability of the HTS in AC and DC applications have been studied. Based on electrical and thermal measurement, the study of quench properties of HTS tapes in magnetic filed includes experiments of minimal quench energy(MQE)and normal zone propagation velocity(NZPV) of YBCO coated conductor in different magnetic field. It has been found that, for the Amperium 8612 double-YBCO tape,the MQE is 0.89?1.91 J and the NZPV is 2.7?40.6 mm/s. The study of quench and stability of HTS coils with degraded part focus on the 3D simulation of DC HTS coils with degraded parts of different sizes and positions, to find the affection on the critical current of the coil, with the software of ANSYS. The study of critical current of AC HTS coils in different cryogenic environment focus on the critical current evaluation of AC HTS coils, based on balance of the AC loss and different cryogenic environment. It has been found that, with the frequency of 60 Hz, the critical current of the coil decreased to 70%?80% of its DC critical current. The study of AC loss of HTS coils with iron core includes experiments and simulations(based on RAA methods) to get the AC loss of HTS coils, in which different iron cores, HTS materials, coil parameters and working conditions have been studied.The above researches are beneficial for the understandings of the quench properties of YBCO coated conductors in magnetic field, the designing of quench protection system, the setting of limiting current and the study of AC loss. Only if all the conditions above were considered, the designed and fabricated coil would have good stability performance.