Comparative analysis of two topologies for rotational superconducting magnetic bearing

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Nov 15, 2013 (3 years and 11 months ago)

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Physica C

1


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. Nicolsky
b,
*

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

b
DEE
-
Poli, UF
RJ, 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 LN
2

and Nd
-
Fe
-
B magnet arrangement is able to produce high

levit
ation
force and stiffness in a Superconducting M
agnetic
B
earing

(SMB)
. However, some parameters in the magnet arrangement have great
influence in the bearing performance. Preliminaries versions of
SMB

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 one
s, 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 for
ce 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.

———

*

Corresponding author.
Tel.: +55
-
21
-
2562
-
8088;

fax: +55
-
21
-
2562
-
8088; e
-
mail: roberto.nicolsky@protec.org.br.

1.

Introduction

Superconducting
M
agnetic
B
e
arings (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
fast
non
-
linearly

with

velocity and the resulting heat
should be

pumped out by a refrigeration system. The usual alternative
is the active magnetic bearing
, but these systems
need a
complicated
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
F
ield
C
ooling (FC) process [1
-
4]. When the
superconductors are cooled without the field of permanent
magnets,
Z
ero
F
ield
C
ooling 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
A
xially
M
agnetized
R
ings (AMR) [2,3] and the
F
lux
S
haper (FS)
[4,5]. In this paper the le
vitation for
ce of the
s
e two

SMB
configurations
(presented in Fig. 1)
is compared for

ZFC
and FC process.


2.

Analysis of AMR and FS topologies

The studied SMB were composed of a Nd
-
Fe
-
B
permanent magnets rotors

(Fig. 1)

and YBa
2
Cu
3
O
7
-


(YBCO) superconducting stators refr
igerated by liquid
nitrogen (LN
2
).
In order to guarantee a better comparative
parameter, AMR and FS topologies have the same
permanent magnets volumes.
The
AMR configuration

has a

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Fig.


1
.

P
er
manent magnet rotors: Axially Magnetized Rings


AMR

(left) and
Flux Shaper


FS
(right).
S
hadowed area
s

correspond to

YBCO

samples

(28mm diameter).


Physica C

2

diameter of 13
0mm
,

while
FS

has 14
0mm

(because it needs
an aluminum encapsul
ation)
. 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
region

under the higher rotor field region
, as
showed by shadowed areas presented in Fig. 1.

Finite Elemen
ts Method (FEM) simulations

were
performed by
2D Axisymmetric static magnetic analyses
.
These simulations are important to determine the region
where YBCO samples
have to be positioned in order to
give
a
higher levitation force. The
results obtained by FEM

calculations are

presented in Fig. 2,
and they
show
that
magnetic induction

for
these
kinds of SMB

is

dual.

The
profile of axial component of magnetic induction of FS
rotor is
approximately

the radial component of AMR rotor
and vice
-
versa
.

The levitation
force measurements were performed by
ZFC and FC refrigeration process for both SMB topologies.
In the ZFC measurements the YBCO was cooled by a
distance of 45mm from the permanent magnet rotor
(
where
its

magnetic field is negligible
)
,

and

the permanent
mag
netic disk
was

approximated to the YBCO stator by a
speed of

0.75mm/s. When a gap of 3.5mm
was

reached the
moving

direction
was

changed, and it return
ed

immediately
with the same speed.
During all this process the levitation
force is measured
and synchroni
zed with the position data
.

The result

for
the
FC
process described above is presented
o
n Fig. 3.

As may be
seen

on this figure,

the
FS

configuration presents a larger levitation force
than AMR.
This result can be attributed to the fact that FS

configurati
on has a greater
radial variation of the axial
component of magnetic induction (see Fig 2) than AMR
.
For FC refrigeration process the YBCO was cooled for an
initial distance of 5mm from the magnetic rotor. Then the
disk was elevated with a constant speed o
f 0.75mm/s until
the vertical distance of 50mm. Finally, the
disk was
brought back until a gap of 2mm. The result for this
situation is presented in Fig.
4, which

s
hows the same
levitatio
n force for both topologies

without considering
their weight forc
es (
FS and AMR mass are, respectively
1.84kg and 2.43kg)
.

3.

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,
et al.
, Physica C 341
-
348(2000) 2607.

[4]

R. de Andrade Jr.
et al., Physica C

408
-
410 (2004) 930.

[5]

G. G. Sotelo

et al.
, IEEE Trans.
App. Supercond. 15 (2005) 2253.




Fig. 2. FEM simulation results for
B

(radial

and

axial components)

for both configurations of SMB for a gap of 4mm.


Fig. 3. Levitation force of the two SMB in
ZFC process.


Fig. 4. Levitation force of the two SMB in a FC process with a
gap of
5 mm. The arrows indicate the direction of the rotor dislocation during
the measurement.