1. Superconductor Power Grid
Science for a
Superconductor Power Grid
A. P. Malozemoff
American Superconductor Corp., Devens MA
USDOE BESAC Meeting
Bethesda MD, July 9-10, 2009 1

2. Superconductors - Basic Facts
Superconductors discovered in 1911
Require cryogenic cooling
High Temperature Superconductors (HTS) discovered in 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™ 2

3. Superconductors: Poised for a Major Role in Addressing Key Challenges in the Power Grid
superconductivity
coal
gas
heat
electrical
generators
electricity
hydro
wind
fuel cells
solar
motors
lighting. heating
refrigeration
information
technology
power grid
transportation
industry
nuclear
fission
2G wires - foundation of grid applications: cables, generators, transformers, FCLs, motors, synchronous condensers, etc. 3

4. US Electric Power System under Severe Stress
The underlying problem: Under-investment in electric power grid while demand for electric power steadily increases
US Energy Consumption (Trillion BTUs)
Total energy
consumption
Electric energy
Source: Cambridge Energy Research Associates 2 1 9 8 7 6 5 4 3
Transmission
Investment
US Transmission Investment (Billion $s)
Source: EIA
Under-investment has spawned a host of technical problems

5. Grand Challenges in Electric Power
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 growing
4. Assure an environmentally clean energy infrastructure

6. 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

7. Enhancing Efficiency through Electrification of Transportation
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)

8. 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
New York then
New York now: it only gets worse!
Lower Manhattan underground infrastructure
(Courtesy of Con Edison)
1913
2003

9. Getting Power into Our Cities
138 kV, 600 m, 574 MVA cable installed
and operating since April 2008 in LIPA grid
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!
Southwire TriaxTM power cable

10. Establishing a Secure and Reliable Grid: an Urgent Need
China …’03, ’04, ’05…
U.S. Northeast ‘03
London ‘03
Moscow ‘05
Athens ‘04
New York ‘99
Denmark ‘03
U.S. West Coast ‘96
Italy ‘03
Delaware ‘99
New Orleans ‘99
Chicago ‘99
Detroit ‘00
San Francisco ‘00
Atlanta ‘99
Northern California ‘01
Significant power blackouts becoming all too frequent

11. Reliability: Controlling Fault Currents in Urban Grids
Faults short out resistive loads, leave grid primarily reactive! R ~ V I
j X
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!
Need a solution, or must drastically reconfigure and break up the grid

12. 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
w/o FCL
w/FCL
Siemens/AMSC 2 MVA FCL
Need a solution, or must drastically reconfigure and break up the grid
Fault current limiters a major opportunity for grid stabilization

13. 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 13

14. 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

15. Comparison of Wind-power Generators n
Renewable Energy:
Comparison of Wind-power Generators n
small,
high power
AMSC/TWMC ATP program addressing design and technology for 8/10 MW generator 15

16. 50% more power, half the weight
Rotating Machinery: Successful Full Power Test of AMSC’s 36.5 MW HTS Motor - Dec. ‘08
AMSC’s 36.5 MW HTS Motor
1.5MW Copper Motor
50% more power, half the weight
Key Advantages:
Less than half the size and weight
Higher efficiency
Less noise
Technology platform established for high power generator for wind-power 16 16

17. Renewable Energy : Need to Carry 100’s of Gigawatts of Green Power to Market
New transmission options needed to bring wind and solar energy to main US markets 17

18. Renewable Energy: DC “Superconductor Electricity Pipeline” for Long-Length, High Power
First DC HTS cable demonstration –
Chubu U., Sumitomo Electric
1000-Mile, 5 gigawatt power equivalents: right-of-way advantage for HTS DC cables 18 18 18

19. The Foundation: Second Generation (2G) HTS Wires - YBCO Coated Conductors
“344 superconductors” cross-section
Laminates – copper, stainless…
Insert – substrate,
buffer, YBCO
AMSC wire: 4.4 mm wide, single-coat
Cu, HTS power equivalents
HTS wire in production – commercially available
AMSC 4 cm Technology 19

20. 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 20

21. 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? 21

22. 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 22

23. AMSC Confidential and Proprietary
Field Dependence of YBCO HTS Wires – Rapid Dropoff of Ic with Field, Temperature
Wire Performance with Magnetic Field Perpendicular to Tape Surface
Need to increase!
Performance data courtesy Railway Technical Research Institute, Tokyo, Japan
AMSC Confidential and Proprietary

24. Control of Grain Boundary Currents by Texturing - Key to Second Generation (2G) YBCO Wire
Grain boundary critical current vs
misorientation angle
AMSC 2G wire architecture:
RABiTSTM process
Dimos, Chaudhari + Mannhart, PR 1990
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! 24

25. 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
D. Van der Laan, SUST 2009 25

26. 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
Vortex:
nanoscale quantum
of magnetic flux
Still significant fundamental issues in existing materials like YBCO 26

27. 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

28. Example: Understanding Properties of High Current Flux Flow State
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
Kraemer et al., IEEE Trans. On Appl. Superconductivity 13, 2044 (2003)
Resistance linear in voltage at short times! 28

29. 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
time
50 V
100 V
150 V
YBCO on sapphire for three different voltages, in liquid N2
(Kraemer et al., 2003) 29

30. 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 30

31. Process Science Challenge – Achieving Uniform Growth through Thick Ex-Situ HTS Films
Through-thickness of hybrid YBCO film
Interface
Tilted YBCO grain
Multi-layer
interface
Top layer has reduced
texture and lower Jc
Lower layer has consistent
texture and Jc
AMSC MOD ex-situ films: decreased performance from poor texture across multilayer interfaces 31

32. 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 ? 32

33. 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 33