[APP2] Magnets, Electric power devices, Rotating machines

[APP2-15] Shielding Characteristics of HTS Rotor Bars in a Rotating Magnetic Field in View of Percolation Limits of State Variables

*Yutaka Terao¹, Taketsune Nakamura¹, Masayoshi Yamamoto¹ (1. Kyoto University (Japan))

Keywords:

HTS Induction/Synchronous Motor,Percolation Characteristics,REBCO Wires,Shielding Current

To realize carbon neutral society in the future, many industrial fields are demanded technical revolutions for reducing greenhouse gas emissions. The approaching points for the technical challenge are, for example, higher efficiency and output density of the electric devices, and one of the most effective ways to realize them is introduction of superconducting technologies into power cables, rotating machines and so on. The authors have been studying induction motors employing high-temperature superconducting (HTS) squirrel-cage rotor winding, i.e., HTS induction/synchronous motors (HTS-ISMs) ¹⁾. And today, the HTS-ISMs can be applied to vehicles, hydrogen pumps, future electric aircraft and so on ^2)-4). The HTS rotor bars possess not only high critical current density, but also self-reliance characteristics for thermal disturbances because of the slanted J-E characteristics. Therefore, the HTS-ISMs are possible to use synchronous operation mode as well as slip operation mode depending on load condition. Focusing on the HTS rotor bars of an HTS-ISM, when rotating magnetic field is applied by three phase stator currents, shielding current loss due to harmonic components of the applied field is generated on the HTS rotor bars in both the induction/synchronous operation modes. Therefore, when an alternating or rotating magnetic field is applied to a high-temperature superconductor, it is essential to investigate the shielding current and the associated energy losses in relation to the thermodynamic state variables of the E–J characteristics—namely, temperature (T) and magnetic flux density (B) in the framework of Gibbs free energy—and to incorporate these insights into analytical methodologies for the HTSs.In this study, particular attention is devoted to the relationship between the percolation transition with respect to T or B, as proposed by Yamafuji and Kiss⁵⁾, and the behavior in the vicinity of the percolation limit, where the lnE–lnJ characteristics shown in figure 1 undergo a transition from exhibiting a convex upward (glass characteristics) to a convex downward (liquid characteristics). We examine how the shielding current characteristics evolve in this regime and discuss their applicability to the design and analysis of HTS devices. In this presentation, the effects are evaluated using an HTS-ISM shown in figure 2 as the representative system.