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Science for a

Superconductor Power Grid

A. P. Malozemoff

American Superconductor Corp., Devens MA

USDOE BESAC Meeting

Bethesda MD, July 9-10, 2009

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Superconductors - Basic Facts

• Superconductors discovered in 1911- Require cryogenic cooling

• High Temperature Superconductors (HTS) discovered in 1986 - cuprates

- 6X higher temperature (135 K vs 23 K)- Less cooling drives commercial economics

• Zero DC electrical resistance- Yields high electrical efficiency

• >100X more power capacity than copper wire of same dimensions

- High power density - reduced size and weight

• Cooling with environmentally benign liquid nitrogen

Copper, HTS @ equivalent 1000 A capacity:

Power density drives system economics

Revolutionizing the Way the World Uses Electricity™

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Superconductors: Poised for a Major Role in Addressing Key Challenges in the Power Grid

superconductivity

coalgas

heat

electricalgenerators electricity

hydrowind

fuel cells

solar

motors

lighting. heatingrefrigeration

informationtechnology

power grid

transportation

industrynuclearfission

2G wires - foundation of grid applications: cables, generators, transformers, FCLs, motors, synchronous condensers, etc.

US Electric Power System under Severe Stress

The underlying problem: Under-investment in electric power grid while demand for electric power steadily increases

Source: Cambridge Energy Research Associates

200019801970196019501940 1990

6

5

4

3

2

1

0

TransmissionInvestment

TransmissionInvestment

US Transmission Investment (Billion $s) US Energy Consumption (Trillion BTUs)

Total energy consumption

Electric energy consumption

Under-investment has spawned a host of technical problems

Source: EIA

• Demand growing relentlessly, doubling by 2050, tripling by 2100, plus need to reduce dependence on foreign oil

1. Need a major enhancement in overall energy efficiency• Increasing grid efficiency• Electrification of transportation• Reurbanization

2. Need major new sources of renewable energy

• Power outages and disturbances cost >10B$ per year

3. Need a secure and ultra-reliable grid

• Environmental issues growing4. Assure an environmentally clean energy infrastructure

Grand Challenges in Electric Power

1. Enhancing Efficiency in the Electric Power Grid

• 7-10% of 1 Terawatt US electric power now lost in ac power grid- Superconductor equipment could cut this by half, save 50 Gigawatts!- Reducing delivery bottlenecks even more impactful

• E. g. superconductor cables bringing 50%-efficient generation to cities, replacing 30%-efficient “reliability-must-run” generators

• Dc Supergrid: a radical leap in grid efficiency - Westinghouse’s ac grid won out over Edison’s dc grid

• Reduced I2R loss by efficient transformers, high voltage- Superconductors break this paradigm

• I2R = 0 enables high dc current, low voltage- First step: delivering renewable energy to urban centers

• Electric vehicles ~2x more energy efficient than gas in original BTU content of oil- ‘A 5% penetration of plug-in vehicles in

Manhattan will create a 50% increase’ in rate of demand growth - ConEd, 11/15/05

- Superconductors key in enabling urban grids to handle this demand

• Maglev an efficient alternative to intracontinental aviation

• Military ship propulsion with HTS motors - 15% efficiency gain at half speed over conventional motors Japanese Maglev flies with HTS coils,

(courtesy CJR)

Enhancing Efficiency through Electrification of Transportation

Enhancing Efficiency by Opening the Urban Power Bottleneck

• Reurbanization driven by rising energy costs

• Requires more power capacity in dense urban areas

• But overhead lines near impossible to permit, underground infrastructure clogged

Lower Manhattan underground infrastructure(Courtesy of Con Edison)20031913

New York then New York now: it only gets worse!

Need underground power cables which are

- High capacity in same X-section- Compact, light – easy to install

by retrofitting existing ducts or boring

- Non-interfering (no EMF or heat)- Low voltage for easy permitting

Superconductors - the ideal solution!

Getting Power into Our Cities

138 kV, 600 m, 574 MVA cable installed and operating since April 2008 in LIPA grid

Southwire TriaxTM power cable

San Francisco ‘00San Francisco ‘00

Chicago ‘99Chicago ‘99New Orleans ‘99New Orleans ‘99

Atlanta ‘99Atlanta ‘99

Delaware ‘99Delaware ‘99

New York ‘99New York ‘99

Detroit ‘00Detroit ‘00

U.S. West Coast ‘96U.S. West Coast ‘96

Northern California ‘01Northern California ‘01

U.S. Northeast ‘03U.S. Northeast ‘03

Denmark ‘03Denmark ‘03

London ‘03London ‘03

Italy ‘03Italy ‘03

Athens ‘04Athens ‘04Moscow ‘05Moscow ‘05

China …’03, ’04, ’05…China …’03, ’04, ’05…

Establishing a Secure and Reliable Grid: an Urgent Need

Significant power blackouts becoming all too frequent

Reliability: Controlling Fault Currents in Urban Grids

• Every added power source adds parallel output impedance– increases fault current

• In large urban grids, fault currents can exceed 60,000 A− approaching maximum breaker capability!

Faults short out resistive loads, leave grid primarily reactive!

R~V

Ij X

Need a solution, or must drastically reconfigure and break up the grid

Reliability: Superconductors Enable “Resistive” Fault Current Limiters

• Superconductors -“smart” materials, switch to resistive state above critical current

• Increased resistance limits current flow

• Many FCLs demonstrated; commercialization beginning

Siemens/AMSC 2 MVA FCL

Need a solution, or must drastically reconfigure and break up the gridFault current limiters a major opportunity for grid stabilization

w/o FCL

w/FCL

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Reliability: Current Limiting Essential for Rewiring Urban Grids

ConEd’s System of Today Powered by Copper Cables

ConEd’s System of the Future with MV Connections

Copper power cables HTS power cables

Project Hydra (AMSC/ Con Edison/Southwire/DHS) demonstrates current limiting cable

Renewable Energy: Opportunity for Off-shore Windpower via HTS Generators

• Off-shore wind - strong and steady- But only 2% of total windpower now off-shore- Opportunity to double windpower production!- Cost the obstacle

• Increased power rating key to economics- Systems up to 5 MW demonstrated- Above 5 MW, conventional generator simply too large and

heavy

• HTS generators offer the needed breakthrough in size and weight to 8-10 MW

- Lowest cost of energy: lowest installed cost per MW, highest efficiency, longest maintenance interval

HTS generators could enable major expansion of offshore windpower

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Renewable Energy: Comparison of Wind-power Generators n

AMSC/TWMC ATP program addressing design and technology for 8/10 MW generator

small,high power

Rotating Machinery: Successful Full Power Test of AMSC’s 36.5 MW HTS Motor - Dec. ‘08

Key Advantages:• Less than half the size and weight

• Higher efficiency

• Less noise

Technology platform established for high power generator for wind-power

1.5MW Copper Motor50%

more power, half the weight

AMSC’s 36.5 MW HTS Motor

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New transmission options needed to bring wind and solar energy to main US markets17

Renewable Energy : Need to Carry 100’s of Gigawatts of Green Power to Market

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Renewable Energy: DC “Superconductor Electricity Pipeline” for Long-Length, High Power

1000-Mile, 5 gigawatt power equivalents: right-of-way advantage for HTS DC cables

First DC HTS cable demonstration –Chubu U., Sumitomo Electric

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The Foundation: Second Generation (2G) HTS Wires - YBCO Coated Conductors

AMSC 4 cm Technology

Cu, HTS power equivalents

“344 superconductors” cross-section

Laminates – copper, stainless…

Insert – substrate, buffer, YBCO

0 100 200 300 400 5000

40

80

120

Ic o

f 3

44

su

pe

rco

ndu

cto

rs

Length (m)

Average Ic = 102AStd. Dev. = +/- 2.3%Max Ic = 109 AMin Ic = 89 A

0 100 200 300 400 5000

40

80

120

Ic o

f 3

44

su

pe

rco

ndu

cto

rs

Length (m)

Average Ic = 102AStd. Dev. = +/- 2.3%Max Ic = 109 AMin Ic = 89 A

AMSC wire: 4.4 mm wide, single-coat

• HTS wire in production – commercially available

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What is Needed to Assure Major Impact and Benefit of Superconductors on Power Grid?

• Existing technology works, but HTS wire and refrigeration costs still limit range of application

• Wire figure of merit: $/kA-m- Now 200 $/kA-m ; need $25/kA-m to undercut copper- Even lower would be better!

• So both cost per meter and current-carrying capacity are critical

- New processes to reduce wire cost- Higher critical currents

• At higher temperatures and fields- Higher Tc? - to decrease refrigeration load

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Science Opportunities: New Superconductors

• Discovery of new superconductors- Track record is exciting – major

discoveries every few years!- New theoretical and calculational

tools, more powerful measurement tools

• Understanding HTS mechanism

HTS cuprates - a supernova – what other supernovae await?

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Science Opportunity: What Kind of New Superconductors Should We Search For?

• Higher Tc, of course- But need to understand flux creep - thermal

activation of vortices from pinning centers

• Reduces critical current in higher Tc materials a lot!

• Lower anisotropy materials- Interlayer coupling dominates flux creep- Can one tune interlayer coupling of existing

highly anisotropic materials?

• May be a more practical route to higher critical currents at higher temperature

Flux creep

Broaden scope of search beyond just higher Tc

AMSC Confidential and Proprietary

Field Dependence of YBCO HTS Wires – Rapid Dropoff of Ic with Field, Temperature

0

2

4

6

8

0 1 2 3 4 5 6Magnetic Field (Tesla)

No

rma

lize

d C

riti

ca

l Cu

rrre

nt

Ic

(T,B

) / I

c(7

7K

,0T

)

80 K

77 K

70 K

65 K

60 K

50 K

40 K

30 K

20 K

Wire Performance with Magnetic Field Perpendicular to Tape SurfaceBB

II

Performance data courtesy Railway Technical Research Institute, Tokyo, Japan

Need to increase!

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Control of Grain Boundary Currents by Texturing - Key to Second Generation (2G) YBCO Wire

Dimos, Chaudhari + Mannhart, PR 1990

AMSC 2G wire architecture:RABiTSTM process

Texturing within ~50 enables Jc(77 K) ~ 3x106 A/cm2 over 100’s of meters –An amazing success, though it has taken 18 years to get to this point!

Grain boundary critical current vsmisorientation angle

Science Opportunity: Understanding Grain Boundaries Better

• Grain boundaries are principal obstacle to current flow in HTS wires

• Contributions of in-plane and out-of-plane components still not well understood

• Amazing reversible behavior under compression

- Ic can recover from 5% of its value!

- Mechanism unknown

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D. Van der Laan, SUST 2009

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Science Opportunity: Vortex Physics

• Pinning vortices – basis for high critical current density

- Much effort on existing materials (e. g. YBCO) during last 15 years

- But much still to do to increase Ic

• Understanding magnetic pinning

• Interplay of columnar and planar pinning centers

• Flux cutting

• Minimizing flux creep

Still significant fundamental issues in existing materials like YBCO

Vortex:nanoscale quantum

of magnetic flux

Science Opportunity: Vortex Dynamics

• Vortex liquid (flux flow state)

- Huge area of HTS B-T phase diagram

- Properties in high drive flux flow state hardly investigated, yet very important, e. g. for fault current limiters

YBCO

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Example: Understanding Properties of High Current Flux Flow State

Kraemer et al., IEEE Trans. On Appl. Superconductivity 13, 2044 (2003)

Discovery of resistance linear in voltage via quench experiment:

• YBCO film on sapphire

• In liquid nitrogen

• 0.1 msec after applied voltage drives film into flux flow state

Resistance linear in voltage at short times!

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Understanding Flux Flow State

• High speed photos of lN2 bubbling reveal novel domain state in flux flow• Length of quenched area increases with applied voltage - mechanism unknown

• Topic being addressed in Superconductivity EFRC

YBCO on sapphire for three different voltages, in liquid N2 (Kraemer et al., 2003)

50 V 100 V 150 V

time

Processing Science for Superconductor Films

• Increasing the limiting cracking thickness for metal-organic deposition (liquid phase) processes

- Key to achieving highest critical current per width need high thickness t: Ic/w = Jc t

- During removal of organics, subtle chemical interactions and kinetics determine limiting thickness

• Achieving high texture in non-magnetic substrate- Texture in low stacking fault energy alloys

• Establishing a single-layer buffer architecture

• Maintaining uniform properties during film growth through precursor layer

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0.0 0.5 1.0 1.5 2.00

100

200

300

400

500

600

7003.4 MA/cm2

Cri

tica

l Cu

rren

t (A

/cm

-w)

Film Thickness (m)

Through-thickness of Through-thickness of hybrid YBCO film - 2006hybrid YBCO film - 2006

Process Science Challenge – Achieving Uniform Growth through Thick Ex-Situ HTS Films

Multi-layerMulti-layerinterfaceinterface

Top layer has reducedTop layer has reducedtexture and lower Jctexture and lower Jc

• AMSC MOD ex-situ films: decreased AMSC MOD ex-situ films: decreased performance from poor texture across performance from poor texture across multilayer interfacesmultilayer interfaces

Interlayer

Tilted YBCO

Interlayer

Tilted YBCO

0.25 µm0.25 µm

InterfaceInterface

Tilted YBCO grainTilted YBCO grain

Lower layer has consistentLower layer has consistenttexture and Jctexture and Jc

Science in Related Technologies

• Cost reduction of cryogenics (cryostat, refrigeration) also key

- Now, refrigeration stations required at several kilometer intervals of ac HTS cable, ten kilometer for dc HTS cable

- How can we achieve 10x distance between refrigeration stations?

• Improved MLI?• Peltier effect – flush out phonons with electric current• Reduced ac and dielectric losses

- >1 kW pulse tube refrigerators ?

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Conclusion

• Superconductivity can play major role in addressing grand challenges of energy generation, delivery and use:

- Engineering foundation in place

• Cables, rotating machines, fault current limiters…

• But important issues remain for broad impact- HTS wire $/kAm and cryogenic costs

• Major science opportunities to address these issues- Discovery of new superconductors, HTS mechanism,

increasing current density, processing breakthroughs…

Support needed for a broad range of superconductor science