Minimising the Usage of Superconducting
Tape in Electrical Machine Applications
Bogi B. Jensen1, Nenad Mijatovic1, Asger B. Abrahamsen2, Chresten
Træholt1
1
2
Department of Electrical Engineering, Technical University of Denmark, Denmark
Department of Material Science – National Laboratory for Sustainable Energy RISØ, Denmark
24-10-2011
SOWiT 2011 Rome, Italy
Technical University of Denmark (DTU)
• Based in Copenhagen, the Capital of Denmark
• 8200 students – 530 faculty – 1040 researchers
• Ranked 4th in Europe by THE based on citations per journal paper
(http://www.timeshighereducation.co.uk/story.asp?storyCode=414302&sectioncode=26)
2
DTU Electrical Engineering, Technical University of Denmark
Installed and expected wind power capacity
in EU and globally until 2030
Trend
Offshore
3GW (2010)
120GW (2030)
On/offshore →
3MW / 10MW
CoE is the driving factor
Source: B.B. Jensen et al. “Influence of rare earth element supply on future
offshore wind turbine generators”, Risø International Energy Conference, 2011.
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DTU Electrical Engineering, Technical University of Denmark
Wind Turbine Trend
“Danish Concept”
DFIG
Full Converter
(PM or other)
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DTU Electrical Engineering, Technical University of Denmark
Direct drive with Full
Converter (PM or other)
Overview of some PM wind turbines
Source: B.B. Jensen et al. “Influence of rare earth element supply on future
offshore wind turbine generators”, Risø International Energy Conference, 2011.
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DTU Electrical Engineering, Technical University of Denmark
The rare earth supply issue
• 97% of RE are mined in China
• China is the top consumer of RE
– Leading to imports in the future
• China is ‘cleaning up’ the industry
– Stricter environmental standards were introduced 1st August 2011
– Constant export quota reductions
– Combat of smuggling
– All resulting in increased prices
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DTU Electrical Engineering, Technical University of Denmark
Rare earth security of supply
• Neodymium
– High risk in the short term 1-5 years
– Medium risk in the medium term 5-15 years
• Dysprosium
– High risk in the short term 1-5 years
– High risk in the medium term 5-15 years
• There is plenty of Neodymium reserves both in China and outside (USA,
Australia and others)
– This does not mean that it is cheap to mine Neodymium
• China claim that their Dysprosium reserves might be depleted within 525 years
• There is Dysprosium in Canada, Australia and South Africa, but when will
these mines start production and at what cost?
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DTU Electrical Engineering, Technical University of Denmark
PM in wind turbines
• A 3MW direct drive wind turbine is estimated to use 2 tons of permanent
magnets
• This is the same as 1000 Toyota Prius
• Should we be worried?
x1000
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DTU Electrical Engineering, Technical University of Denmark
Drivetrain comparison – Rare earth usage
Cu
&
Fe
PM
Geared
HTS
0
25kgR/MW1
Have not
been
proposed
0
60kgR/MW1
25gR/MW2
0
250kgR/MW1
100gR/MW2
Hybrid
Direct drive
1m
R
2RE
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= 0.27mR-B-Fe
usage in an HTS machine depends heavily on the topology
DTU Electrical Engineering, Technical University of Denmark
Why use Multi-Pole Generators?
• The converter is indifferent
(to a certain extent)
• Power is independent of
pole numbers
• Voltage is independent
of pole numbers
• Traditionally: weight
(and cost) savings!
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DTU Electrical Engineering, Technical University of Denmark
Source: www.avantis-energy.com
Core Back Thickness
• The flux path is from one pole to the next.
ˆ  2Bˆcb Acb  2Bˆcbla dcb
1
d cb , stator 
p
1
d cb , rotor 
p
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DTU Electrical Engineering, Technical University of Denmark
PM Direct Drive Generator
2 Poles
• The mass of the nacelle can be significantly reduced
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DTU Electrical Engineering, Technical University of Denmark
10 Poles
End windings
• Copper and HTS end winding length is reduced
2 Pole
Multi-Pole
Source: www.mandc.co.za
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DTU Electrical Engineering, Technical University of Denmark
Multipole HTS wind turbine generator
Source: H. Ohsaki et al. “Electromagnetic Characteristics of 10 MW Class
Superconducting Wind Turbine Generators”, ICEMS, 2010.
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DTU Electrical Engineering, Technical University of Denmark
Mass, HTS length and price as a function of
pole number
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DTU Electrical Engineering, Technical University of Denmark
Cost of HTS and PM in a 10MW wind turbine
• If 400km of 4mm HTS tape is assumed for a 10MW wind turbine
generator
• With a current carrying capacity of 80A and a price of €100/kAm, this
gives €8/m
• The cost of the HTS tape for a 10MW would therefore be €3.2 million
• In addition the cryostat, cryocooler etc. will have to be added
• PM price today? €100-150/kg
• If 10 tons of PM is required for a 10MW wind turbine
• The cost of the PM for a 10MW would be €1-1.5 million
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DTU Electrical Engineering, Technical University of Denmark
Future cost of HTS must/will come down
• It is not unlikely that the price of HTS tape will come down to €15/kAm
• This would result in €480,000 for a 10MW wind turbine
• This would be competitive with PM technology
• But it is clear that the usage of HTS tape must be minimised!
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DTU Electrical Engineering, Technical University of Denmark
The Superwind project
• Aims at assessing HTS machines for wind turbines
• Particularly for large scale direct drive wind turbines
• Constructed a prototype demonstrator
– Assessing HTS coils
– 1G – BSCCO (Tc ~ 110K)
– 2G – YBCO (Tc ~93K)
– Not yet investigated MgB2 (Tc ~39K)
• The prototype and some results are presented in what follows
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DTU Electrical Engineering, Technical University of Denmark
Entire setup
•
•
•
•
Stationary field winding (normally rotor)
Rotating armature (normally stator)
Belt drive
Cryostat with liquid N2
Source: N. Mijatovic et al. “High Temperature Superconductor Machine
Prototype”, ICEMS, Beijing, China 2011.
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DTU Electrical Engineering, Technical University of Denmark
Armature
• A 2 pole, 22kW induction machine
• ID: 160mm
• Stack length: 150mm
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DTU Electrical Engineering, Technical University of Denmark
Cryostat
•
•
•
•
•
•
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Thermal insulation (300K and 77K)
Vacuum (10-5 mbar)
Multi Layer Insulation (MLI)
Effective airgap of 10mm
Torque Transfer Element
Contains the HTS winding
DTU Electrical Engineering, Technical University of Denmark
HTS field winding
• Mounted on a core which can contain up to 10 race track coils (4mm)
Source: N. Mijatovic et al. “High Temperature Superconductor Machine
Prototype”, ICEMS, Beijing, China 2011.
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DTU Electrical Engineering, Technical University of Denmark
HTS coils
• The HTS coils are equipped with voltage measurement, temperature
sensors and Hall probes
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DTU Electrical Engineering, Technical University of Denmark
High Temperature Superconductors
• The superconducting state is limited by
– Critical flux density Bc
– Critical current density Jc
– Critical temperature Tc
• HTS materials can be characterised
by IV curves


J
E[V / m]  E0 

J
(
B
,
T
)
 c

n ( B ,T )
• E0 is the electric field at the
critical current (1μV/cm)
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DTU Electrical Engineering, Technical University of Denmark
VI curves for individual coils installed in the
machine


J
E[V / m]  E0 

J
(
B
,
T
)
c


n ( B ,T )
Source: N. Mijatovic et al. “High Temperature Superconductor Machine
Prototype”, ICEMS, Beijing, China 2011.
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DTU Electrical Engineering, Technical University of Denmark
Series connected coils
• Coil 3 reaches its critical current first then coil 5
• Matches simulations that show the flux density
• Coils 2 and 6 are not fully utilized
Source: N. Mijatovic et al. “High Temperature Superconductor Machine
Prototype”, ICEMS, Beijing, China 2011.
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DTU Electrical Engineering, Technical University of Denmark
Employing multiple power supplies
• Increased the airgap flux density by 12% without optimisation
Source: N. Mijatovic et al. “High Temperature Superconductor Machine
Prototype”, ICEMS, Beijing, China 2011.
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DTU Electrical Engineering, Technical University of Denmark
Topology optimisation
• Adopted topology optimisation, as used to optimise the placement of
structural elements in aeroplane wings
• Where should the superconductor be placed?
• What type of superconductor should be used
– Depending on price and properties
Source: N. Mijatovic et al. “Coil Optimization for High Temperature
Superconductor Machines”, IEEE Trans. Appl. Supercond., Vol. 21, No. 3, 2011.
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DTU Electrical Engineering, Technical University of Denmark
Combining topology optimisation with
multiple power supplies
• A fixed airgap flux density of 3.0T was maintained
• The maximum coil volume was fixed
– Hence engineering current densities are crucial
• Combining topology optimisation with multiple power supplies showed a
theoretical potential save of more than 50%
Source: N. Mijatovic et al. “Coil Optimization for High Temperature
Superconductor Machines”, IEEE Trans. Appl. Supercond., Vol. 21, No. 3, 2011.
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DTU Electrical Engineering, Technical University of Denmark
Conclusion
• HTS machines might be the answer to large wind turbines
– Lighter generator
– Less RE demand by a three orders of magnitude
• The usage of HTS material must be minimised
• The usage of HTS tape can be minimised by:
– Choosing the right machine topology for the right application
– Topology optimisation of the HTS tape placement
– Allowing multiple power supplies
– Using more expensive tape in the more critical areas
• Thank you
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DTU Electrical Engineering, Technical University of Denmark
VIND I ØRESUND
This presentation is part of an EU Interreg project, which is informing about
projects connected to Wind in the Øresund-region of Eastern Denmark and
Southern Sweden.
A collaboration between the Technical University of Denmark (DTU) and The
Faculty of Engineering at Lund University (LTH).
The project Superwind (www.superwind.dk) is funded in part from the
Globalization grant of the Technical University of Denmark (DTU) funds.
The authors would like to acknowledge the support and contribution provided
by the Center for Electric Technology (CET), Risø DTU and RUAG Space.
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DTU Electrical Engineering, Technical University of Denmark