Electromagnetic Forces Relationship Between Bulk High Temperature Superconductor Magnet And Linear Three-phase Windings

Bulk high temperature superconductor (HTSC) can be magnetized as bulk high temperature superconductor magnet (HTSM) and is able to be applied as predominant "quasi-permanent magnet" in rotary or linear synchronous motor systems for its potential performance of high flux-trapping characteristics. The advantage of this high temperature superconducting (HTS) motor technology is to decrease the volume and weight of motors, as well as increasing motors’efficiency and force density. The superconducting levitation, superconducting guidance and superconducting propulsion will probably be integrated in the HTS Maglev transportation system if a HTS linear motor is employed. Combining with the current research background, this paper carried out the study on electromagnetic forces (thrust force and normal force) characteristics of bulk HTSC linear motor.Firstly, it has been explored that how to obtain higher-field bulk HTSM as the secondary for the better linear motor under the present popular existing magnetization experimental setup. Three magnetization methods were designed and the peak trapped flux densities of bulks HTSM by these three methods were compared. Based on the optimal magnetizing method, we further improved the existing magnetization setup by simulation and experiments. Higher trapped flux, optimal magnetization and improved experimental platform was finally obtained by adding two square sheets of iron onto the magnetic poles of existing magnetization setup. This magnetization operation process is time-saving and efficient by this improve setup.Based on the optimized magnetized method and the improved setup, the electromagnetic forces between bulk HTSM and flat single-sided linear three-phase windings were studied in details. It was found that bulk GdBCO which has the higher critical current density yielded larger thrust force acting as secondary of linear motor compared with bulk YBCO. More force experiments, under conditions of different exciting currents, different critical current densities, relationships between the size of bulk HTS and pole pitch, different secondary magnetic field distributions, reveal that forces between primary and secondary increases with the increase of bulk magnet size within one pole pitch as one characteristics of bulk high temperature superconductor linear motor. And the force curves will be distorted while the size of bulk approximately equals the size of one pole pitch, which can be explained as followed. The large-size bulk HTSM was not usually located in the same pole pitch of the stator completely and the opposite force will be produced on the area of the different pole pitch. So, the thrust force will be efficiently improved when the relationship factor between the size of bulk HTSC secondary and pole pitch of the motor primary are considered. It is recommended that the bulk HTSM with size that approximately equals one pole pitch length is selected as the secondary and the optimal magnetization method also should be adopted in the superconducting linear motor using bulk HTSM as the secondary. Further, the electromagnetic forces of the bulk three-seeded HTSM were studies as the secondary of linear motor. The results show that, thrust force is larger when the bulk three-seeded HTSM is located along the vertical direction of linear motor than the case along the parallel direction of linear motor, which strongly implies that the size of pole pitch is a significant design parameter of the bulk HTSM type linear motor. The mothod that locating large sized bulk multi-seeded magnet or several bulk magnets on the same pole pitch in the vertical direction of linear motor will benefit to improve thrust force no matter how the bulk HTSCs is fabricated or its growth characteristics is shown.At last, the relationship between the size of bulk HTS and pole pitch of stator is calculated by Multiphysic Comsol, which verified the experimental results. We further calculated the relationship between trapped flux of bulk HTSM and thrust force, and the relationship between stator current of primary and thrust force. Some conclusions are predicted on prototype design suggestions of the bulk HTSM secondary, three-phase windings and full-superconducting linear motor and its potential applications.The work in this paper will provide the experimental data and design guidance for the dynamic research of bulk HTSM type linear motor and the feasible prototype of the HTS Maglev propulsion system.