Abstract Body

The Magnetic bearings support rotors without contact by the magnetic force. Therefore, friction, noise, and energy loss can be eliminated. In this study, the HTS magnetic bearings are used, featuring a rotor consisting of permanent magnets and the HTS on the stator side. The rotor is levitated by the pinning force of the HTS which interacts with the magnetic flux from the rotor. This pinning force allows the maintenance of both levitation and guidance directions stability without the need for a control system [1]-[5].

On the other hand, the stability of the system under vibration, such as when mounted on a vehicle, has not been clearly understood. In this paper, the entire HTS magnetic bearing system is vibrated by an external force. It is assumed that the HTS magnetic bearing system will be mounted on a vehicle or other moving object and applied as a superconducting flywheel for power storage.

The rotational characteristics will be measured under three conditions: without vibration, with vibration, and with step vibration. The flux variation, calculated from the measured the rotational characteristics and the oscillation of the rotor, will be used to evaluate stability. The flux variation is one of the factors of rotational attenuation of the HTS magnetic bearing rotor [6][7].

The HTS magnetic bearing rotor is levitated by the pinning effect when HTS is cooled in a magnetic field. The HTS used in this study is a yttrium-based superconducting bulk material (YBaCuO). The rotor consists of a ring-shaped neodymium permanent magnet with an attached yoke. The yoke improves the utilization of the magnetic flux and improves the vibration suppression effect of the rotor.

In the experiment with vibration, the entire HTS magnetic bearing system is mounted on a bogie and subjected to vibration. The vibration is applied to the entire device for 100[s]. The amplitude is x = 300[mm], the period is T = 2.0, 4.0[s], and the height of the step is 20[mm]. The levitation gap of the rotor is g = 8 [mm].

Figure 1 shows the comparison of rotational attenuation. In the vibration experiment, the oscillation and rotational attenuation of the rotor increased within the vibration range for both periods T = 2.0 and 4.0 [s]. Comparing the results with and without steps, the rotational attenuation increased when the step was present. This is likely because not only lateral vibration, but also vertical vibration was added to the rotor when it passed through the step.

Comparing the period T = 2.0 and 4.0[s], the displacement of the rotor was larger, and the amount of the flux variation was larger for period T = 2.0[s]. The oscillation of the rotor causes a change in the flux linked to the HTS. This flux variation on the HTS surface is considered to have increased the rotational attenuation due to the electromagnetic force.

However, in the vibration experiment, the rotation remained stable after the vibration range, and the rotational attenuation was not significantly different from that in the experiment without vibration. Additionally, the levitation of the rotor was also maintained.

References

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[2] J.Hull, M.Murakami,“Apprications of bulk high temperature superconductors ”, in Proc of IEEE, vol. 92, no. 10, October 2004, pp1705-1718

[3] M. Okano, N. Tamada, S. Fuchino, I. Ishii, T. Iwamoto, 2000 Numerical analysis of a superconducting bearing IEEE Trans Appl Supercond, vol.10, no. 1, pp909-912

[4] Z. Yu, G. Zhang, Q. Qiu, L. Hu, D. Zhang, M. Qiu, 2015 Analysis of levitation characteristics of a radial-type high-temperature superconducting bearing based on numerical simulation IEEE Trans Appl Supercond,vol. 25, no. 3, 3600605

[5] F. C. MOON, “SUPERCONDUCTING LEVITATION”, JOHN WILEY & SONS, NEW YORK, (1994)

[6] R.Taniguchi,S.Ishida,K. Yagi and S.Ohashi, “Analysis of the Amount of Flux Variation on the HTS Surface by the Oscillation of HTS Magnetic Bearing Rotor,” IEEE Transaction on Magnetics(Volumes: 59,Issue: 11, 8001004, 2023).

[7] K.Yagi,R.Taniguchi,S.Ishida and S.Ohashi, “Effects of the External Vibrations on Rotational Stability of the HTS MagneticBearings,”2023 IEEE International Magnetic Conference(INTERMAG), Sendai, Japan, 2023, doi:10.1109/INTERMAG50591.2023.10265098

Figure 1. The comparison of rotational attenuation

Keywords: Magnetic Levitation, High-Temperature Superconductor, Flux Pinning