Three superconducting stacks made of 120 REBCO coated conductor tapes were each fabricated and assembled to obtain several REBCO modules. Their levitation responses over two different permanent magnet (PM) guideways were investigated by experiment and finite element simulation. For the experiment, a test rig was developed that can measure the force in the three directions for any given relative movement between the REBCO stacks and the PM guideway. For the finite element simulation, a 2D H-formulation was adopted. To treat the high aspect ratio of REBCO tapes, an anisotropic homogenization technique was used. The agreement between the measurements and the simulations is good, thus validating the modeling methodology. It was observed from the experiment and simulation results that the perpendicular field contributes to the levitation force whereas the parallel field is responsible for the guidance force, as a result of the existence of anisotropy on the local magnetic stimulation. Based on that, promising REBCO modules including both longitudinal and transverse arrangements of REBCO stacks were proposed and tested, in terms of providing a significant levitation force with the lateral stability preserved. Moreover, a pre-load process able to suppress the relaxation of the levitation force was put forward. To conclude, this study outlines explicit principles to obtain an appropriate layout of coated conductor stacks that could be effective for practical magnetic levitation operation.

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Coated conductor magnet, as the onboard magnet of the electrodynamic suspension (EDS) train, is deemed promising due to its relatively high operating temperature, low cooling cost, and good mechanical tolerance, making the liquid-helium-free high-temperature superconducting (HTS) EDS train possible. In order to promote the progress of the HTS EDS train, this work aims at designing, fabricating and testing a coated conductor magnet as the onboard magnet of EDS train. The HTS magnet is designed with the comprehensive considerations of the electromagnetic calculation, thermal-mechanical coupling analysis, as well as the heat load estimation. The magnet is conduction-cooled without any coolant. A radiation shield was used to reduce the heat leakage, enabling the cryogenic system to provide a better low-temperature environment for the magnet. Through a deliberate design, the magnet was fabricated, including two HTS coils and the tailored cryogenic system. Afterwards, the electromagnetic and thermal performances of this magnet were tested and analysed in detail. It was proven that the magnet can be cooled to below 15 K; besides, the magnet has been successfully charged to 240 A. Further increase in the current is possible because of the high safe margin of the critical currents for both the HTS magnet and its current lead, although a slight performance degradation was observed on two double-pancake coils inside the magnet. The present study will provide useful implications for the design and application of onboard HTS magnets in EDS train.

Thermal effect will greatly affect the engineering performance of high temperature superconductors (HTSs) due to its strong dependence of electromagnetic parameters upon the local temperature. To advance the understanding of such thermal effect, a validated three-dimensional (3-D) strong-coupled electromagnetic-thermal model for HTS bulk was established in commercial finite element software COMSOL, which ensures the easy access and universality of the model. Jc(B,T) was employed to reflect both magnetic field and thermal field dependences of HTS in this model. In addition, the thermal transient equation and convective boundary condition were employed with experimentally measured HTS thermal conductivity and heat capacity to describe the thermal flux exchange between HTS and cryogenic medium. As an example of application, the established electromagnetic-thermal model was tailored to study the dynamic characteristics of a linear HTS magnetic levitation (maglev) bearing. The methodologies to numerically study the dynamic response of the linear HTS maglev bearing under free vibration state and typical operating excitations, e.g. earthquake, track irregularity and crosswind, were put forward in this paper. The influences of field cooling height, pre-load and ambient temperature, were also studied and promising methods to improve the system stability were put forward according to the obtained conclusions. The above results are reasonable and keep in concert with former experimental and theoretical studies. Moreover, some results which are inaccessible in the 2-D models, for instance, the thermal field distribution inside HTS bulk, can also be obtained due to the versatility of 3-D model. To conclude, the established HTS electromagnetic-thermal model could serve as a flexible and extensible simulation tool to study various applications of HTS bulk. Besides the application in linear HTS maglev bearing, which is systematically studied in this paper, other potential applications such as thermal analysis of HTS bulk in pulse magnetization process, HTS bulkbased electrical machines, can also be expected in future work.

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The use of metallic sheets as the insulator in a coated superconductor coil is able to increase its turn-to-turn contact resistance for shortening the charging/discharging delay while preserving the self-protection ability. To theoretically understand and predict the properties of the metal-insulation coils, we developed a thermo-electromagnetic model, in which a modified equivalent circuit for electrically representing the metal-insulation coils is built to take the effect of insulator into account. The effectiveness and versatility of this model are verified by different experimental scenarios, e.g., charging, sudden-discharging, and overcurrent. Enabled by the validated model, we carried out a set of case studies and observed that, (a) the metal-insulation coil with a low resistivity and high thermal conductivity metallic insulator is preferable to achieve a better thermal stability; (b) there exists an optimal insulator thickness for realizing the shortest charging delay, but a thicker insulator is superior for realizing a stronger thermal stability; (c) contact resistivity of over 104 μΩ· cm2 can weaken the current sharing in the radial direction, which would deteriorate the thermal stability of the metal-insulation coils, although it can significantly suppress the charging delay, implying that a tradeoff is always needed to balance the charging delay and thermal stability when determining the contact resistivity. These findings, mostly being inaccessible from the experiments, provide guidance toward practical applications of metal-insulated coated superconductor coils.

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