This paper presents the design and innovative test of a Linear Induction Motor (LIM) to be used in the urban Superconducting Magnetic Levitated (SML) vehicle, named MagLev-Cobra. This levitation method, based on the flux pinning property of High-Temperature Superconductors (HTS) in the proximity of rare-earth permanent magnets, has constraints related with the lifting forces. This issue is even more critical as there is no control of the levitation gap, which changes according to the load. The motor design is based on analytical equations and computational simulations by Finite Element Methods (FEM). An innovative workbench for tests was developed to measure values of interest, such as end effects, forces, electrical currents, magnetic flux densities, and others. Numerical and experimental results support the desired performance of the proposed LIM.

The superconducting magnetic bearing ability to sustain a stable levitation gap without a control system is its main advantage and finds an application niche on urban transportation, as demonstrated by the Maglev Cobra project. However, the use of YBCO bulks brings major drawbacks, such as the absence of a quality-standard large scale production process, hampering this application to further advance into commercialization. On the other hand, REBCO tapes have reached large scale production worldwide and have surpassed bulks in critical currents and pin-ning capacities, making them a possible substitute for bulks in large scale applications. This paper proposes a novel superconducting magnetic bearing made of REBCO tapes. The bearing here proposed uses tape segments, with partially opened slits, to form superconducting jointless loops. This allows larger flux linkage and thus provides larger levitation forces than stacked segments. Multiple loops are stacked side by side to form two symmetrical coils, with better volume usage than a single loop coil. Simulations are carried out to foresee the levitation force behavior. Force measurements are made in order to evaluate the new bearing performance with the Maglev Cobra permanent magnet guideway. The results reinforce the thesis that tapes could substitute bulks in superconducting magnetic bearings.

Transient voltage distribution due to steep-fronted surges must be taken into account during the machines design as it can lead to main and turn insulation failure. In medium voltage machines, the end-windings region has a considerable percentage of the coil length and plays an important role during transient studies. This paper has the purpose of verifying the influence of end-windings on the transient voltage distribution by using a three-phase simulation model in which transient magnetic fields and electric circuit elements are coupled. The transient simulation and the calculation of the electrical parameters used in the model are done employing the Finite Elements Method (FEM). To verify the influence on the results, simulations for different surge rise times are performed, considering and neglecting the end-windings model. As main results, the intercoil and interturn voltages are analyzed for all turns from the three phases of one winding group. The model is validated by measurement results. It is shown that the end-windings, indeed, affect the transient voltage distribution for both, interturn and intercoil voltages, regarding the rate of rising (slope), instant, and the amplitude of the peak voltages. Moreover, all three phases are affected by the end-windings, especially for the turn-to-turn voltages.

The normal force that exists between primary and secondary of a linear motor plays an important role in Magnetically Levitated (MagLev) trains. In the particular case of the Superconducting Magnetic Levitation (SML) method, based on the diamagnetic property of high-temperature superconductors (HTS) in the proximity of rare-earth permanent magnets, this issue is even more critical, as there is no control of the levitation gap, which changes according to the load. In this paper, the previous experience of traction systems of MagLev trains in commercial operation serves as a background for the study and will be reviewed. The experience of other SML projects will also be considered to reach the proposed topology, similarly to the process of genetic evolution. The proposed solution for the normal force issue consists of a Linear Induction Motor (LIM) optimized for an urban SML vehicle. Analytical equations and simulations with the finite element method (FEM) are presented. An innovative workbench for velocity tests was developed to measure the parameters of interest. Simulation and experimental results confirm the improved performance of the proposed LIM. The final results with the short primary linear induction motor, designed and tested, showed excellent results. The LIM can be qualified as 3 times low: low-cost solution, for low-speed SML vehicles and with low-normal force amplitudes.

Low critical temperature superconducting coils can conduct persistent currents with almost no losses, as the technique to make joints is well developed and the resistive losses are negligible. The replacement of these superconductors by high-temperature superconductors may greatly reduce refrigeration costs. However, even though the technique for making these joints has greatly developed over the last years, there are still inherent difficulties associated to that process. Coils made with partially slit loops of high temperature superconducting tape have no joints, and therefore can conduct current in persistent mode. Since there are no terminals, its current must be induced through magnetization techniques, for instance, by the means of a transformer. The occurrence of persistent current is related to the voltage in the sample, making it interesting to study the voltage behavior for different regions of operation. In this work, a jointless 2G loop was magnetized with pulse magnetization from which the curves of voltage and current as functions of time were obtained. After several tests, it was possible to divide the superconductor behavior into three different stages of operation, depending on the current levels reached: for low current values, the material behaves as a perfect inductor; for current values near the critical current, it behaves as an RL circuit; and for higher values, resistance dependent on the temperature has to be taken into account. A direct relation between persistent current and the arise of a dissipative state was noted and the highest values of persistent current were observed when the pulse was intense enough to produce significant temperature variations in the sample.