Abstract Body

Future carbon neutral society demands us major improvement of infrastructures with greenhouse gas emissions. Especially, focusing on some infrastructures such as factories, power plants and substations, rotating machines can be found in many places. Nowadays, 40-50% of electric energy is consumed by electric motors in all over the world. While almost 95% is usual value of motor efficiency, if we can improve 1% motor efficiency, it is possible to reduce 80 billion kWh and CO2 emissions by 32 million tons in all over the world [1]. Therefore, some research groups like electric machines and superconducting (SC) applications have been studying to realize higher efficiency rotating machines. In general, well known motor loss factors are copper loss, iron loss, mechanical loss at bearings, stray loss and so on. Then, SC wires contribute to reduce copper losses when we apply the wires to field windings because of the zero-dc resistance of the SC wires. And iron loss can be reduced by means of high-quality electromagnetic steel sheet. However, it is impossible for rotating machines to do without bearings. In other word, mechanical loss by bearings is quite difficult to remove.

Magnetic bearings can contribute to reduce mechanical frictions of usual bearings and therefore increase of efficiency of rotating machines is expected in the future. However, it is known that the magnetic bearings have complicated control systems as well as a merit of no mechanical contact.

SC magnetic bearings (SMBs) can simplify the components of the usual magnetic bearings via pinning effect between superconductors and permanent magnets (PMs). The physical phenomena means that it is possible for us to obtain stable magnetic levitation without complicated control systems.

We have been proposing a SMB using a PM and a ring shape layered REBCO SC tapes [2, 3]. The proposing SMBs have a potential to enlarge radial direction easily in comparison with bulk superconductors. And now we gave been investigating φ140 mm SMBs shown in Fig. 1.

In this presentation, we report some electromagnetic and mechanical characteristics of the φ140 mm SMBs using PMs with different magnetization direction such as radial or axial directions. And the effect of radial direction stabilization using other components using a PM and a cylindrical superconductor.

References

[1] N. Tachi, H. Koibuki and K. Takahashi, “Fuji Electric’s Top Runner Motor – Loss-Reduction Technology fof “Premium Efficiency Motor”,” Fuji Electric Review, Vol. 61, No. 1, pp. 31-35, 2015  

[2] Y. Terao, S. Fuchino and M. Ohya, "Stiffness and loss characteristics of superconducting magnetic bearings using layered HTS tapes and a permanent magnet." Physica C: Superconductivity and its Applications, Vol. 614, 1354401, 2023.

[3] Y. Terao, S. Fuchino and M. Ohya, “Electromagnetic Characteristics of Stacked Superconductors and Permanent Magnets Applying for Magnetic Bearings,” TEION KOGAKU (Journal of Cryogenics and Superconductivity Society of Japan), Vol. 58, No. 5, pp. 245-251, 2023, in Japanese.

Acknowledgment

This research was conducted as a commissioned project as JPNP14004 by New Energy and Industrial Technology Development Organization (NEDO).

(a)Layered Ring Shape Superconductor (b) Ring Permanent Magnet

(b)Fig. 1. Components of aφ140 mm superconducting magnetic bearing.

Keywords: Permanent magnets, Rotating machines, Superconducting magnetic bearings, Superconducting tapes