applications of high performance permanent magnets

REPM08, September 8-10, Crete, Greece

www.electronenergy.com

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



(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



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



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


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



Vector MapFlux Density Map

Halbach Dipole Structure



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



A Example of Halbach PM Quadrupole


www.electronenergy.comMagnetic Mangles

45o Position

90o Position 135o Position

0o Position



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



Surface Coupler with 12 Alternating Poles

Flux density along the center line of the air gap

Flux in T

esla


www.electronenergy.comConcentric Coupling System

Applications include mixers and pumps, especially for pharmaceutical, chemical and medical applications.



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



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



Flux Contours from EM FEA with PM bias and control flux.

High Temperature PM Biased Magnetic Bearings



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


www.electronenergy.comRadial Bearing Test

Apparatus



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



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



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.



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.



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

applications of high performance permanent magnets

Documents

b magnets

b d h d b r b d h d

high temperature results

high temperature sm

radial bearing test

air gap flux density

t air gap flux

total gap flux