development of high temperature magnetic bearings

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National Aeronautics and Space AdministrationGlenn Research Center

Texas A&M Vibration Control and Electromechanics Lab

ASME/IGTI Turbo Expo June 9-13, 2008 Berlin, Germany

HIGH TEMPERATURE, PERMANENT MAGNET BIASED, FAULT TOLERANT, HOMOPOLAR MAGNETIC BEARING

DEVELOPMENT

Alan Palazzolo, Randall Tucker, Andrew Kenny, Kyung-Dae Kang, and Varun Ghandi

Department of Mechanical Engineering, Texas A&M University, College Station, TX

Jinfang Liu and Heeju ChoiElectron Energy Corporation, Landisville, PA

Andrew ProvenzaNASA Glenn Research Center, Cleveland, OH

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Presentation Outline

1. Discuss NASA/Electron Energy Corporation (EEC) Funded Small Business Innovative Research (SBIR) Project and Goals

2. Describe EEC High Temperature Permanent Magnets and the Benefits of Use

3. Introduce a High Temperature Homopolar Radial Magnetic Bearing Design

4. Describe a Test Apparatus for Radial Bearing Bench Testing

5. Discuss Some Bench Test Results

6. Show Solid Model of the a High Temperature Test Rig/Technology Demonstrator

7. Describe the High Temperature PM Motor

8. Conclude

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8. Conclude

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SBIR Phase II Project:Novel High Temperature Magnetic Bearings (MB) for Space

Vehicle Systems

• Utilize EEC Patented 550°C SmCo PM’s developed under previous US Air Force funded research to advance the SOA MB (and motor) technology.

• Develop Research Rig/Technology Demonstrator that includes a motor, two radial MB’s, one thrust MB, and backup bushings all operating in a 540°C environment.

• Improve upon SmCo 2:17 PM properties by tweaking Cu and Co composition. Improve PM manufacturing techniques.

• Design State-of-the-Art Radial MB that is PM-biased, has a low axial profile, has very low eddy current losses, is optimized for weight, and is fault-tolerant to loss of poles and amplifiers.

• Design, build, and use an improved apparatus for determining the current and position stiffness as well as load capacity of high temperature radial MBs.

PHASE II GOALS – EEC and Texas A&M Univ.

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8. Conclude

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PM Bias Offers a Significant Reduction in Magnetic Bearing

Power Requirements

• Permanent Magnets carry majority of static rotor system weight instead of an MB coil or coils and provide bias gap force.

• This reduces real power (I2R) losses dramatically.• Copper wire resistance is 3 times higher at 550°C than at 22°C.

Cu Resistivity vs. Temperature

0.0

1.0

2.0

3.0

4.0

5.0

6.0

-300 -200 -100 0 100 200 300 400 500 600

Temperature °C

Cu

Re

sis

tiv

ity

(u

OH

M-c

m)

(25,1.744)

(550,5.302)

5.302/1.744 = 3.04

304% increase in resistivity at 550°C

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0

100

200

300

400

500

600

700

800

900

1000

0 1 2 3 4 5

Force (kN)

Po

we

r (W

)27°C 121°C 260°C 399°C 538°C

NASA/TAMU 2003 R&D100 Award-Winning, All-Electromagnetic, 12-pole Heteropolar, High Temperature Radial Magnetic

Bearing.

This bearing’s DC Power Requirements for Force Production. *Note - this data takes into account a gap growth and a reduction in Hyperco50 lamination properties with temperature as well as an increase in Cu resistivity.

PM Bias Offers a Significant Reduction in Magnetic Bearing

Power Requirements

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Project Related History of Permanent Magnets

• Prior maximum operating temperature of conventional SmCo magnets was only 300°C

• US Department of Defense (DoD) initiated the More Electric Aircraft program, which required magnets with maximum operating temperature more than 400°C

• EEC with funding from DoD developed a series of sintered SmCo 2:17 magnets with a operating temperatures to 550°C (US Patent # 6,451,132)

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Typical Composition: Sm(Co1-u-v-wFeuCuvZrw)z

Sm (Co0.757+xFe0.100Cu0.110-xZr0.033)7.0

• For high temperature magnets with maximum operating temperature of 550°C:• Fe content u ≤ 0.1, Cu content v ~ 0.1, and Zr content w ~ 0.03

• Maximum operating temperature is related to the ratio (1-u-v-w)/u. The higher this ratio is, the higher the maximum operating temperature will be

• Z is the ratio between Sm and transition metals. Optimum ratio z leads to the 2:17 phase, which is the key to get good magnetic properties at temperature

• Cu and Zr contents are critical to obtain an optimum nanoscale microstructure for obtaining high intrinsic coercivity at temperature, but are non-magnetic elements.

• Under scope of SBIR project, the magnetic properties of EEC SmCo 2:17 with varying amounts of Co and Cu were to be conducted to find Cu minimum.

Chemical Compositions of EEC High Temperature Magnets

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Permanent Magnet Grades

• High temperature magnets require a coating (such as Ni-plating) if continuously used above 400°C.

• Commercially available NdFeB magnetics available with (BH)max of 54 MGOe. But TM of only 80°C. Theoretical limit for NdFeB is 64 MGOe.

• Commercially available SmCo 2:17 magnets have a (BH)max of 32 MGOe. Theoretical limit for SmCo is 34 MGOe.

Grades Br (kG) (BH)max (MGOe) TM (°C)

EEC 24-T400 10.2 24 400

EEC 21-T400 9.5 21 400

EEC 20-T500 9.2 20 500

EEC 18-T500 8.7 18 500

EEC 16-T550 8.5 16 550

EEC 15-T550 8.0 15 550

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Typical Demagnetization Curves of EEC High Temperature T550

Magnets with a Maximum Operating Temperature of 562ºC

Sm(Co0.757Fe0.100Cu0.110Zr0.033)7.0

Load Line Slope: Bd/Hd = AgLm/AmLg

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8. Conclude

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Solid Model of the Radial Bearing Actual Radial Bearing

PM-Biased Radial Bearing Design Details Back Iron

Pieces

Permanent Magnets

Dual Lamination Stacks Rotor Lamination

StackSmall Air Gap

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EEC magnet arc segments glued together.

EEC magnet arc assemblies stuck in place on outer diameter of bearing lamination stacks.

PM-Biased Radial Bearing Design Details

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Flux Contours from EM FEA with PM bias and control flux.Upper Y coils are “fully on” and bottom “fully off”.


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Amp-Turns

Average Gap Control Flux

(TESLA)

1000 F 70 F

0 0.00 0.00

135 0.20 0.23

270 0.31 0.40

405 0.37 0.45

540 0.42 0.50

Parameter New Design Original Design

Bearing OD 23.75 cm 23.11 cm

Bearing Length

8.18 cm 10.08 cm

Bearing Weight

208 N 267 N

Air Gap Flux at 540°C

.53 T(18%

improvement).45 T

Linear Load

Capacity

656 lbs(31%

improvement)500 lbs

Notable parameters from bearing design

optimization

• Prediction of how many Amp-Turns needed to produce a certain control flux density.

• At 22°C, FEA Bias Flux Density = 0.98 T, At 540°C, it’s 0.53 T.

• 540 Amp-Turns will not be sufficient to completely drive gap flux density to zero.


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Temp C

Pole No.Applied

VoltsApplied Amps

Resistance

M-Ohms

HIGHTEMP

538 1 500 25 20.0

538 2 500 140 3.6

538 3 500 120 4.2

538 4 500 180 2.8

538 5 500 200 2.5

538 6 500 200 2.5

ROOMTEMP

76 1 500 0 infinite

76 2 500 0 infinite

76 3 500 0 infinite

76 4 500 0 infinite

76 5 500 0 infinite

76 6 500 0 infinite

Radial Bearing Stator 1 of 2. High Potential Insulation Integrity Test Results.

Radial Bearing Electromagnet Wire Insulation Integrity Testing

• Silver Wire with Triple S-glass Insulation.

• Insulation integrity testing using classic high-pot “high-potential” testing.

• Voltage is applied between Hyperco50 lamination stack and coil wire.

• Low resistance measurement indicates voltage breakdown (insulation compromised)

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8. Conclude

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Radial Bearing Test Apparatus

Stiffer ‘monolithic’ rotor supports that replaced the ball screw assemblies.

Radial Bearing Test Apparatus

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8. Conclude

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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).

• Opposite applied current polarity to sets of 3 circumferentially sequential poles.

• cs = 233 N/A (52 lb/A). cs = 182 N/A (40 lb/A) was predicted.

Some Room Temperature Resultsfrom Radial Bearing Bench Tests

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Some High Temperature Resultsfrom Radial Bearing Bench Tests

A high temperature test was performed yielding the following results as listed in the paper:

• Max. Force Output: Force at 13.3 amps with centered rotor and 6 on, 6 off max. force producing condition was 2800 N (629 lbs), which is approx. 86% of RT result.

• Max. Position-related force: 2220 N at 0.38 mm rotor offset. Yields approximate ps = 5.8 kN/mm, which is about 44% of RT result.

• Test temperatures: PM’s were 493°C, Shaft was 350°C, Ceramic Layer on Poles was 366°C.

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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 (lb

s)

4 Load Cells

Dr.Kenny's Prediction using FEA

calculation from circuit model (0.65*Hc)

2 Load Cells

Stiff Support Internal

Moment

Bearing Force

Dummy Load Cell

Reaction Force

Load Cell Reaction Force

Force Transmission Yoke with only one functional load

cell.Radial Bearing Force vs. Current at Room

Temperature

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8. Conclude

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Solid Model of High Temperature Test Rig Components

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8. Conclude

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Pictures of High Temperature PM Motor being driven to determine voltage and current waveforms for controller procurement.

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8. Conclude

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CONCLUDING REMARKS

• EEC has developed PM’s that remain quite magnetic at 550°C.• EEC has developed manufacturing techniques to create arched

segments for use in MB and Motor Designs.• TAMU has designed a Radial MB that should, based on preliminary

bench testing, operate as predicted at 550°C.• Actual Radial MB Air gap flux density at XXX°C was 0.Y T.• A new and improved MB characterization apparatus was designed,

built and successfully used to determine current and position stiffness as well as force capacity of a high temp MB.

• A research rig/technology demonstrator is almost completed.• A PM Motor has been built for demonstrator and bench tested.

High Temperature Test Rig will be completed and available for use as a sales tool in demonstrating the technology to potential customers.

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ADDITIONAL SLIDES

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High intrinsic coercivity Hci at elevated temperatures to resist demagnetization Low temperature coefficient of Hci (β)

Straight-line demagnetization curves at maximum operating temperatures TM

Magnets can be made for any specified TM up to 550°C with highest possible (BH)max

High temperature magnets require surface coating (such as Ni-plating) if used above 400°C continuously

High temperature magnets still belong to Sm2TM17 magnet family

Key Features of EEC High Temperature Magnets

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(BH)max Versus Maximum Operating Temperature

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development of high temperature magnetic bearings

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