REPM08, September 8-10, Crete, Greece
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Applications of High Performance Permanent
Magnets
J. F. LiuElectron Energy Corporation
924 Links Ave, Landisville, PA 17538, USA
Phone: 1-717-898-2294 Fax: 1-717-898-0660
REPM08, September 8-10, Crete, Greece
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(1) Some Magnet Design Considerations
(2) Permanent Magnet Dipoles
(3) Permanent Magnet Quadrupoles
(4) Magnetic Mangles
(5) Magnetic Couplings
(6) High temperature hybrid magnetic bearings
(7) Summary
Outline
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Permeance Coefficient Pc
Also known as load line or operating point
It is related to the dimensions of the magnets and the associated magnetic circuit
In the magnetic circuit, a magnet will operate at a specific point on its extrinsic demagnetization curve:
Pc = Bd/Hd
Br
Bd
HdHcPc=Bd/Hd
Some Magnet Design Considerations
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Why straight-line demagnetization curves?
Application with load line #1: Both magnets are okay to use
Application with load line #2: Only magnet #1 is suitable
Bd1
Normal demagnetization curve for magnet #1
load line 2
Br
Hc0
Knee
load line 1
Bd2
Hd1 Hd2
Br
Hc
Normal demagnetization curve for magnet #2
REPM08, September 8-10, Crete, Greece
www.electronenergy.comPermanent Magnet Dipoles
Halbach PM Dipole Structures:
Bg = Br ln(OD/ID)ODID
There is no upper limit for air gap flux density in Halbach dipole structures according to above equation. But in reality it would be limited by:
(1)The realistic size
(2)The demagnetization effect
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Vector MapFlux Density Map
Halbach Dipole Structure
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4 Tesla PM prototype Halbach cylinder was prototyped in Japan.*
EEC has produced many small Halbach structures for a variety of applications.
Sintered Sm-Co or high Hci Nd-Fe-B magnets are good choices
*M. Kumada et al, PAC2001, 3221.
Halbach Dipole Structure
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A Example of Halbach PM Quadrupole
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www.electronenergy.comMagnetic Mangles
45o Position
90o Position 135o Position
0o Position
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Adjustable magnetic quadrupoles as reported by Fermi lab and SLAC*:
Diametrically magnetized SmCo 2:17 tuning rods
Tuning rods rotation changes the strength of field gradient
* J. T. Volk et al, PAC2001, p217
Adjustable Magnetic Quadrupoles
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Surface Coupler with 12 Alternating Poles
Flux density along the center line of the air gap
Flux in T
esla
REPM08, September 8-10, Crete, Greece
www.electronenergy.comConcentric Coupling System
Applications include mixers and pumps, especially for pharmaceutical, chemical and medical applications.
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Solid Model of the Radial Bearing Actual Radial Bearing
Back Iron Pieces
Permanent Magnets
Dual Lamination Stacks
Rotor Lamination StackSmall Air Gap
High Temperature PM Biased Magnetic BearingsSupported by NASA Glenn Research Center, EEC/TAMU designed and
built a PM-biased hybrid high temperature magnetic bearing that can operate at 1000 F
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High temp magnet arc segments assembled together.
Magnet arc assemblies stuck in place on outer diameter of bearing lamination stacks.
Magnet
Demagnetization Curves of T550 High temp
magnet
High Temperature PM Biased Magnetic Bearings
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Flux Contours from EM FEA with PM bias and control flux.
High Temperature PM Biased Magnetic Bearings
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AmpsAmp-Turns
Average Gap Control Flux
(TESLA)
550°C22°C
0 0 0.00 0.00
3.75 135 0.20 0.23
7.5 270 0.31 0.40
11.25 405 0.37 0.45
15 540 0.42 0.50
Parameter New Design
Bearing OD 23.75 cm
Bearing Length
8.18 cm
Bearing Weight
208 N
Air Gap Flux at 22oC
0.98 T
Air Gap Flux at 550°C
0.53 T
Linear Load
Capacity2910 N
Design parameters
• Bias flux subtracted from total gap flux.
• At 22°C, FEA Bias Flux Density = 0.98 T, At 550°C, it’s 0.53 T.
• 540 Amp-Turns will not be sufficient to completely drive gap flux density to zero.
PM-Biased Radial Bearing Design Details
Control Flux Density as a function of Amp-Turns
REPM08, September 8-10, Crete, Greece
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Apparatus
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0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.180
200
400
600
800
1000
1200
1400
1600
1800
2000
Position in mm
For
ce in
N
0 5 10 150
500
1000
1500
2000
2500
3000
3500
Current in Amps
Forc
e in
N
• Negative position stiffness (nps)– measured radial bearing force vs. rotor position.
• Test performed with zero control current.
• nps = 13.3 kN/mm (76 lb/mil).
• All 12 poles on two stators energized to determine max. possible current stiffness (cs).
• Rotor held as best as possible in geometric center position.
• cs = 233 N/A (52 lb/A).
Some Room Temperature Resultsfrom Radial Bearing Bench Tests
Force vs. Rotor Position
Force vs. Control Current
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A Comparison of Analytical and Experimental Room Temperature
Radial Bearing Test Results
0
200
400
600
800
1000
0 5 10 15 20Current (A)
Forc
e (lbs)
4 Load Cells
Dr.Kenny's Prediction using FEA
calculation from circuit model (0.65*Hc)
2 Load Cells
Radial Bearing Force vs. Current at R.T.
• Reasonably good agreement between 3D FEA and 4 Load Cell Data.
• Analytical result at 10 Amps is 7% higher than actual
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Some High Temperature Results
from Radial Bearing Bench Tests• Test temperatures: PM’s were 493°C, Shaft
was 350°C, Ceramic Layer on Poles was 366°C.
• Max. Force Output: Force at 13.3 amps with centered rotor was 2800 N (629 lbs), which is 86% of RT result.
• Max. Position-related force: 2220 N at 0.38 mm rotor offset. Yields approximate nps = 5.8 kN/mm, which is about 44% of RT result.
•SmCo magnets and control coils works very well at elevated temperatures.
REPM08, September 8-10, Crete, Greece
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Solid Model of High Temperature Test Rig Components
We are in a process of building this test rig. It will be ready later this year.
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Summary
A new hybrid high-temp magnetic bearing was designed and built using high temperature Sm-Co magnets. It will be tested using a specially design test rig
Permeance Coefficient of magnets in the electromechanical system should be carefully considered in the design and material selection stage
Halbach principles can be used in many different applications