Key issues for power applications J e Overall current density J e of conductor, not just of superconductor Performance in field Multiple filaments for AC applications Anisotropy of J c with respect to field direction Cost! Conductor itself Cooling (AC losses) Scalability of fabrication Mechanical Strength, bend radius
HTS –perovskite ceramics Cu OBa Y YBCO - YBa 2 Cu 3 O 7 B2223 - Bi 2 Sr 2 Ca 2 Cu 3 O
Engineering Implications Requires near single-crystal microstructure by complex processing, Oxide requires furnace treatment in controlled oxygen atmosphere, in silver, Highly anisotropic resulting tape: Along and across tape, Sensitive to magnetic field direction!
AMSC & Sumitomo AMSC & Sumitomo have a reciprocal licensing agreement American Superconductor 55 filament (B2223) tape Sumitomo (B2223) tape
AMSC B2223 Manufacturing Plant Larger billets, Process automation, Longer strands, Multi-dies, Faster line-speed, Combination of process steps Larger billets, Process automation, Longer strands, Multi-dies, Faster line-speed, Combination of process steps Began volume production in early 2003 Began volume production in early 2003 Full capacity could be 20,000 km/year, now 900 km/year Full capacity could be 20,000 km/year, now 900 km/year
How much does it cost to buy the wire to carry 1000 Amps a distance of 1m? Copper: 6 $/kA.m – 22 $/kA.m depending on current density (400 – 100 A/cm 2 ) Superconductors typically quoted at J c and at 77K and either zero magnetic field or self field. Cryogenic OFHC copper can be 0.06 $/kA.m. NbTi is approx. 0.9 $/kA.m in liquid helium. Price/Performance $/kA.m
Reduced Manufacturing Costs ($/m) and Increased Wire Performance (current carrying capacity) 1995199619971998199920002001200220032004 $/kA.m 0 200 400 600 800 1000 1200 Price/Performance Ratio, $/kA-m Worlds First HTS Wire Manufacturing Plant Opened By AMSC Price/Performance $/kA.m 200 $/kA.m
B2223 & Commercial Products At $50/kAm (77K) price/performance ratio significant markets would be enabled (it was thought in ~1999): Utility Generators (>100MVA) Utility Generators (>100MVA) Ship Propulsion Motors and Generators (>5MW) Ship Propulsion Motors and Generators (>5MW) Wind Turbine Generators (>4MW) Wind Turbine Generators (>4MW) Urban T&D Power Cables Urban T&D Power Cables Industrial Magnetic Processing Industrial Magnetic Processing Significant worldwide industry in B2223 American Superconductor, Innova, Nordic Superconductor, Sumitomo Electric, Vacuumschmelze, Trithor Bought and shut down by AMSC in 2002
Magnetic Field High magnetic field reduces current carrying capacity Lower temperatures enhance current carrying capacity Transformers, cables and FCLs are low magnetic field devices B2223 at 27K carries twice the current, so $/kA.m reduces to 100 $/kA.m.
Diboride & YBCO YBCO and similar compounds have had research worth $$billions devoted to their physics and processing. MgB 2 was discovered in January 2001; physics now entirely understood. Both can be made in: Tape geometry Massive lumps for new motor designs
Making Diboride tape Cu-sheathed tape transverse cross section Tube filling with MgB 2 powder Wire drawing and/or rolling Flat rolling Long lengths can be now fabricated irregular cross section Simple sintering ~700C
In situ B+Mg with Fe barrier in Monel Sheath With iron –tough to make multifilament- most likely be cabled, (twisted) monofilaments for low AC loss conductor, working on Outer sheaths of Monel, Cu/Ni, and Cu to improve stabilization. Hyper Tech Research
Magnesium Diboride (MgB 2 ) Advantages No weak-link effects, low anisotropy No weak-link effects, low anisotropy Easy to fabricate wires, films: <$10/kA.m potential Easy to fabricate wires, films: <$10/kA.m potential Challenges T c < 40 K (77 K applications like cables, transformers not viable) T c < 40 K (77 K applications like cables, transformers not viable) High field applications such as NMR not viable High field applications such as NMR not viable Possible applications in 20-30K range for modest field environments, e. g., rotating machinery
YBCO Coated Conductor Rolled, textured Nickel tape (Ni-W) Oxide buffer layer, preserves texture YBCO (or analogue, e.g. HoBCO), preserves texture Near single crystal 100s of metres long Near single crystal 100s of metres long <$10/kA.m potential, but extraordinary plant cost <$10/kA.m potential, but extraordinary plant cost
YBCO YBCO precursor YBCO oxygenation and conversion
YBCO Coated Conductor tape Active programs in US, Japan and Europe Examples of results in 2001: 122 A (75 K) over 1 m by LANL 122 A (75 K) over 1 m by LANL World record for meter length World record for meter length 50 A over 10 m by Fujikura 50 A over 10 m by Fujikura World record for 10 meter length World record for 10 meter length Over 60 m :Fujikura Over 60 m :Fujikura Worlds longest processed tape Worlds longest processed tape
YBCO CC Technical Issues Adequate uniformity over length Stability to over-currents or cracks Adequate current in MOD films Mechanical properties – spalling, cracking Stability of metal-oxide epitaxial interface Deposition rate for ion beam and laser processes Thicker than 3 micron YBCO ? …but must have that 10 $/kA.m process!
Cryogenics High AC power is intrinsic to transformers Cables have high losses: so need cryogens Conduction-cooled designs need exploring 20-24K and 27K-60K for other applications Thermal reservoirs need investigating to peak-shave cryogenics capital costs Reducing the capital cost of cryogenics is as important as their efficiency for grid markets
Cooling & Purchase Costs There is a trade-off between cryogenic capital cost and materials capital cost – colder running means less material required but more cryogenics. The cheaper the superconductor, the higher the optimum operating temperature. Comparing different materials therefore requires a whole-system comparison Competition between materials is application dependent Transport applications are always more attractive
Cost Prediction Source: Mulholland et al, DOE June 2003
ABB HTS Transformer 100 MVA, 225 / 20 kV oil free, liquid nitrogen 68K 20% lower weight 80% lower load losses 5% smaller volume Short circuit reactance 50% of conventional 25% over-loadability without accelerated ageing 150% first cost 90% lifecycle cost Short circuit current limitation in first half wave, self restoring FCL 11 m 135 000 kg 5m5m
Other HTS Transformer Benefits Reduced need for load tap changer units Reduced system VAR requirements Reduction in capacitor banks With a generator, reduced VAR enables additional generator capacity so reduced capital cost of generator
ABB Conclusions With current costs for energy and equipment, an open loop refrigeration system is the most economical. The mechanical refrigeration industry is not currently able to meet performance targets required for a commercial Utility product. –Cryocoolers are too expensive, maintenance intervals are too short, and production methods are not cost effective. –The number of competitors in the field is limited, and the companies are generally small operations. –Production scale-up and comprehensive global service could be problematic Near term market too small to justify continuation of project!
Waukesha/ORNL Project Waukesha 24.9kV to 4.2kV $10m project 2x overload capability FCL capability 1 MVA pilot at 25K with cryocooler
Transformers Lifetime Cost of Ownership in $/kW 2000 ABB SPI Phase I Analysis Cu (330 K) @ 300 A/cm 2 HTS (68 K) 200$/kAm MgB 2 (25 K) Losses60 Cryo- Wire5 Total65 5 25 50 80 510 34 5 50 Adapted from Paul Grant EPRI
ORNL HTS Transformer High utilization and high cryocooler efficiency required to get energy savings (RAND) Feasible with 10- year payback if <15$/kA.m at 77K. (Lawrence Assc.)
Energy Efficient Transformers High-copper section designs Domain-refined steels Ultra-thin iron laminations High-field (1.7T) iron alloy core Metallic glass or amorphous iron core Lowest first-cost purchasing prevents adoption of any of these technologies. www.efficient-transformers.org
Primary Benefit The primary benefit in a superconducting transformer is the Fault Current Limiting capability. Therefore, make FCLs first!