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Physica C

Comparative analysis of two topologies for rotational superconducting magnetic bearing

G. G. Sotelo,a.J. L. da Silva Neto,b.R. de Andrade Jr.,a,b.A. C. Ferreira,a.R. Nicolskyb,[*]

aPEE-COPPE,UFRJ, C.P. 68504, 21945-970 Rio de Janeiro, Brazil

bDEE-Poli, UFRJ, C.P. 68515, 21945-970 Rio de Janeiro, Brazil

Elsevier use only: Received date here; revised date here; accepted date here

Abstract

The combination of high temperature YBCO bulks refrigerated by LN2 and Nd-Fe-B magnet arrangement is able to produce high levitation force and stiffness in a superconducting magnetic bearing. However, some parameters in the magnet arrangement have great influence in the bearing performance. Preliminaries versions of superconducting magnetic bearing with Nd-Fe-B magnets were shown in previous work and the obtained results allowed to make improvements in the new prototypes. These new SMB prototypes are more efficient than the previous ones, due to their lower weigh, and because they may produce higher levitation force, by optimization in the magnetic circuit. Two topologies of superconducting magnetic bearings having the same permanent magnets volumes are compared: flux shaper and axially magnetized rings. As expected from previous works the flux shaper configuration presents a larger levitation force in a zero field cooling measurement. But, both configuration presents the same force in field cooling measurements. © 2006 Elsevier Science. All rights reserved

Keywords: SMB; Nd-Fe-B; YBCO; magnetic bearing.

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Physica C

  1. Introduction

Superconducting magnetic bearings (SMB) are useful to high-speed rotational devices, like flywheels, because they can operate at high speed with very small energy losses and self-stability [1]. Mechanical bearings fail in high speeds because the energy dissipation increases with the square of velocity and the resulting heat has to be pumped out by a refrigeration system. The usual alternative is the active magnetic bearing that needs an active electronic control. The SMB, composed by permanent magnets and type II superconductors, are self-stable due the flux pinned inside the superconductors in a field cooling (FC) process [1-4]. When the superconductors are cooled without the field of permanent magnets, zero field cooling process (ZFC), there is a maximum levitation force, but the bearing stiffness is small [3]. In previous papers the levitation force and stiffness of two SMB configurations was studied, the axially magnetized rings (AMR) [2,3] and the flux shaper (FS) [4,5]. In this paper we compare the levitation force of this two SMB configurations in ZFC and FC process.

  1. Superconducting magnetic bearings

The studied SMB were composed of a Nd-Fe-B permanent magnets rotors and YBa2Cu3O7- (YBCO) superconducting stators refrigerated by liquid nitrogen (LN2). In order to compare the AMR rotor with the FS rotor, the same superconducting stator is used for both. The two topologies have the same permanent magnets volumes. The FS configuration, Fig. 1a, has a diameter of 140mm while AMR, Fig. 1b, has 130mm. The height of permanent magnets rings for both topologies are 10mm. The YBCO blocks, with 28 mm diameter and 10 mm height, were mounted in a ring under the higher rotor field region.


Finite Elements Method (FEM) simulations shown that these rotor topologies are complimentary. The profile of axial component of magnetic induction of FS rotor is equal to the radial component of AMR rotor and vice-versa for another, Fig. 2.




  1. The levitation force of SMB prototypes

In the ZFC measurements, Fig. 2, the flux shaper configuration presents a larger levitation force as expected form the previous works [3,5]. But the FC measurement, Fig. 3 shows exactly the same behavior and force. The levitation force measurements were conducted in automatized test rig with 0.75 mm/s approaching velocity.

  1. Conclusion

Acknowledgments

The authors acknowledge the financial support of the Brazilian agencies CNPq and FAPERJ.

References

[1]J. R. Hull, Supercond. Sci. Technol. 13 (2000) R1.

[2]R. Nicolsky et al., Physica C 341-348 (2000) 2509.

[3]R. de Andrade, A. Ripper, D. F. B. David, and R. Nicolsky, Physica C 341-348(2000) 2607.

[4]R. de Andrade Jr. et al., Physica C408-410 (2004) 930.

[5]G. G. Sotelo, A. C. Ferreira, and R. de Andrade Jr., IEEE Trans. App. Supercond. 15 (2005) 2253.

[*] Corresponding author. Tel.: +55-21-2562-8088; fax: +55-21-2562-8088; e-mail: .