Abstract Body

Rotating machines such as motors and generators are indispensable for world industrial and transport applications, today. On the other hand, it is known that electric energy consumptions by motors reach 40-50% in all over the world. Therefore, motor loss reduction is one of the key issues for future carbon neutral societies on the earth. In general, main motor losses consists of copper loss, iron loss and mechanical losses. The copper losses at the rotor side can be reduced by using superconducting wires because of their quite lower ohmic resistance. And air cored machine structures are helpful for obtaining lower iron loss machines. Furthermore, the mechanical losses are often generated at bearing part. Also, in case of the use at very low temperatures, it is difficult for usual mechanical bearings to operate with grease because of freeze. Some research groups have been trying to realize bearings without lubricant oils by means of non-metal materials, however, critical break through has not been found, yet. Therefore, development of bearings operated at every temperature range with lower mechanical losses are quite important factors for rotating machines to increase their efficiencies and reliabilities.

The magnetic bearings using permanent magnets (PMs), iron and copper coils have been developing to reduce mechanical contacts between rotating part and stator part by magnetic levitation [1]. And the magnetic bearings can be operated without mechanical losses; however, they require complicated feed back control systems to keep stable rotation and magnetic levitation in the installed systems.

Magnetic levitation without complicated control by flux pinning is one of outstanding merits of superconductors; therefore, superconducting magnetic bearings (SMB) consist of bulk superconductors and PMs are one of famous applications using the flux pinning. The SMBs are expected to install flywheel energy storage systems [2], artificial satellite systems [3], and so on.

We have been studying the SMBs consist of PMs and ring shape stacked high temperature superconducting tapes to apply rotating machines [4]. In comparison with the SMBs using PMs and bulks, the radius of the ring can be expanded freely. This is because larger bulk superconductors require larger electric furnaces and are more difficult to machine. Also, focusing on critical current density of the superconducting wires are sometimes higher than that of bulk superconductors and it means that total superconductor quantity of the SMBs using the stacked superconductors is smaller than that of the bulk SMBs though the electromagnetic forces are even among the two SMBs. Therefore, the SMBs using stacked superconductors have a potential to be applied to larger rotating machines as well as usual superconducting applications with easier manufacturing processes. Since the previous study, we have been investigated some characteristics like electromagnetic forces, and rotation characteristics at 1800 rpm using devices shown in Fig 1 [4]. In this presentation, we report some mechanical investigation results like electromagnetic forces, spring constant and rotation losses. Especially, rotation losses are estimated with different rotation speed. And then, the comparison results with the SMBs with bulk superconductors are also discussed.

References

[1] Siemens: SIMOTICS Active Magnetic Bearing, https://www.youtube.com/watch?v=02xuPAaAEB0&t=101s（Accecced on 2023-08-19）
[2] S. Mukoyama, et al., "Development of superconducting magnetic bearing for 300 kW flywheel energy storage systems,” IEEE Trans. Appl. Supercond. 27(2017) 1-4
[3] Y. Sakurai, T. Matsumura, H. Kataza, S. Utsunomiya and R. Yamamoto: " Estimation of the heat dissipation and the rotor temperature of superconducting magnetic bearing below 10 K,” IEEE Trans. Appl. Supercond 27 (2017) 1-4
[4] 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) Accepted (2023), in Japanese

Acknowledgment

This research was conducted as a commissioned project as JPNP14004 by New Energy and Industrial Technology Development Organization (NEDO). And we also appreciate for Dr. Makoto Okano for discussing effective arrangement of stacked superconductors and PMs.