Our research group has researched and developed a High Temperature Superconducting Induction/Synchronous Motor (HTS-ISM) as a high efficiency and high torque density motor. The HTS-ISM can realize high-performance rotating characteristics that cannot be achieved with conventional (normal-conducting) motors by effectively utilizing the zero resistance and nonlinear current transport characteristics of the HTS conductors [1]. However, a major problem with the HTS motors is the need to cool them to cryogenic temperature, and the event of having to stop the rotation system when the cooling system fails is not practical. In order to overcome the above problems, a group of Kyoto University proposed a normal conductor/superconductor hybrid squirrel-cage winding and showed the possibility of continuous drive near the superconducting critical temperature [2]. By using this winding, when the HTS conductor is in a superconducting state, a superconducting current is induced in the conductor, realizing high performance rotation. On the other hand, if the conductor transitions to the normal conducting state, the current will automatically transfer to the normal conductor, reducing the output and allowing the rotation to continue. Based on the preliminary results, the analytical study on the continuous drive of the HTS-ISM from room temperature to the cryogenic temperature is carried out [3].

In this study, a prototype HTS-ISM with a maximum synchronous output of 6 kW at a temperature of 77 K (atmospheric boiling point of nitrogen) and a rated slip output of 1.5 kW at room temperature was fabricated. The motor consists of a copper wound stator and a superconducting BSCCO/copper hybrid cage rotor. As a result of the rotation test, not only the synchronous rotation at the temperature of 77 K but also the continuous slip rotation test at room temperature were succeeded. At the presentation, detailed test results such as current waveforms and transition drive tests between the superconducting state and the normal conducting state will be reported.

[1] G. Morita, T. Nakamura and I. Muta, Supercond. Sci. Technol., 19(6) (2006) 473
[2] T. Nakamura et al., Supercond. Sci. Technol., 22(4) (2009) 045022
[3] T. Nakamura et al., TEION KOGAKU (J. Cryo. Soc. Jpn.), 51(5) (2016) 178 (in Japanese)

Acknowledgements:
We would like to thank Mr. Takuro Ogasa, Mr. Jun Matsuura, and Mr. Yasushi Takashima for their cooperation in the experiments.

Keywords: Fault tolerance, HTS-ISM, Non-superconducting rotation, Super-&normal-conductors hybrid cage