Superconducting Generators
for Large Wind Turbine:
Design Trade-Off and Challenges
Philippe J. Masson, Vernon Prince
Advanced Magnet Lab
Palm Bay, FL
CEC ICMC 2011
CEC-ICMC
2011, S
Spokane,
k
WA
June 16th, 2011
http://eetweb.com/wind/wind-turbines-go-supersized-20091001/
3
www.magnetlab.com
1 of 41
Outline
Introduction
Off Sh
Off‐Shore wind power generation
i d
ti
Current technology
Superconducting generators
gy
Technology trade‐offs
Application to off‐shore wind
Ongoing projects
Ongoing projects
Conclusion
3
•
•
•
•
•
•
•
•
www.magnetlab.com
2 of 41
Outline
Introduction
Off Sh
Off‐Shore wind power generation
i d
ti
Current technology
Superconducting generators
gy
Technology trade‐offs
Application to off‐shore wind
Ongoing projects
Ongoing projects
Conclusion
3
•
•
•
•
•
•
•
•
www.magnetlab.com
3 of 41
Superconducting Machines Features
Courtesy of Siemens
4
3
www.magnetlab.com
4 of 41
In 2011…
Sc Machine built in 1966
• First
First Sc. Machine built in 1966
• 45 years later, still no commercial applications…
li ti
– Conventional machines are good for 99% of the i d ti l
industrial applications
li ti
• Decent efficiency, very robust and reliable, inexpensive
– HTS machines have drawbacks
HTS
hi
h
d
b k
Cooling required at all time
High capital cost
High capital cost
Reliability not proven
p
p
More complex with more parts
Cryogenic system perceived as high risk component
3
•
•
•
•
•
www.magnetlab.com
5 of 41
Markets for HTS Machines
• Applications with requirements in terms of specific power/torque and efficiency that cannot be matched b
by conventional machines
l
h
AML Energy
http://www amsc com/products/motorsgenerators/shipPropulsion html
http://www.amsc.com/products/motorsgenerators/shipPropulsion.html
American Superconductor
3
AML – ESAero – NASA GRC
www.magnetlab.com
6 of 41
Outline
Introduction
Off Sh
Off‐Shore wind power generation
i d
ti
Current technology
Superconducting generators
gy
Technology trade‐offs
Application to off‐shore wind
Ongoing projects
Ongoing projects
Conclusion
3
•
•
•
•
•
•
•
•
www.magnetlab.com
7 of 41
Global Energy – A “Hungry” Market
Existing and expanding global economies have a large appetite for Energy…
…with no signs of letting up!
250
Projections
History
(1012 KWh)
200
+45%
World Primary Energy Consumption
 USA-20007
150
100
50
0
1980
1985
1990
1995
2000
2005 2010
2015
2020
2025
2030
Sources: History: EIA, International Energy Annual 2005 (June-October 2007). Projections: International Energy Agency World Energy Projections Plus (2008)
“In order to meet the 45% increase in projected demand, an investment of over $26 trillion will be required …”
3
•
www.magnetlab.com
8 of 41
Energy “Landscape” and Superconductivity
• Power Generation
– Cost per Kilowatt Hour!!!!!
– Minimal carbon footprint
Minimal carbon footprint
• Power Distribution
– Power Transmission
– Grid Management
– Energy Storage
• Power Use
– Energy Efficiency
FFor all, cost, efficiency and environment are ll
t ffi i
d
i
t
the driving factors!
Superconductivity is a very attractive p
y
y
technology
3
www.magnetlab.com
9 of 41
Price Range of Renewable Electricity (2008)
Solar
3
www.magnetlab.com
10 of 41
Why Off-Shore Wind?
•
D l
d l
t th
/l d
Developed close to the consumer/load
– Most of the big cities are located near the coast
•
High power availability
– Very steady wind is available off‐shore
•
Installation and connection cost is very high
– Need to reduce the number of turbines
• Increase single turbine power output
– Need to keep nacelle mass as low as possible
• Foundation cost
• Installation cost
Cost of maintenance is very high
– Need very reliable turbines
– Need to reduce required maintenance needs/servicing
•
http://www.ngpowereu.com/news/
europes-push-on-offshorerenewables/
Need lighter, reliable drivetrain / generators
3
•
www.magnetlab.com
11 of 41
Offshore Wind – poised for growth
E
ff h
i df
ti 1 100 MW tt with 70‐90% ith 70 90%
• European offshore windfarms
are generating 1,100 MWatts
availability. Deep water offshore is progressing.
•Off‐shore wind is on its way in the US with a very large potential market.
DOE-NREL
Over the next 5 years Offshore Wind will be a significant
component of the US Renewable Energy spectrum
3
www.magnetlab.com
12 of 41
Outline
Introduction
Off Sh
Off‐Shore wind power generation
i d
ti
Current technology
Superconducting generators
gy
Technology trade‐offs
Application to off‐shore wind
Ongoing projects
Ongoing projects
Conclusion
3
•
•
•
•
•
•
•
•
www.magnetlab.com
13 of 41
Current Issues of Conventional Drivetrains
• Reliability
– Gear boxes
• major cause of failure, high maintenance needs
major cause of failure high maintenance needs
– Thermal cycling
• Insulation fatigue
• Power output
– Low efficiency at fractional power
– Power factor
– Controls
• Scalability
– Limited specific power
d
f
– Availability of rare‐earth magnets
3
www.magnetlab.com
14 of 41
Next Generation
•
•
Elimination of Gearbox
Permanent Magnet Generators
10 MW
Copper Wound-Coil
with Gearbox
> 500 Tons
Next Generation ‐ No Gearbox
Permanent Magnet
> 320 Tons
3
Conventional Turbine Generator
www.magnetlab.com
15 of 41
Large Wind Generators
L
i d t bi
d i df
Large wind turbines are desired for offshore deployment. Lightweight, reliable generators are paramount to the economic feasibility of such systems
economic feasibility of such systems.
•
•
100
Sizes > 10+ MW @ 10 RPM
No gearbox > higher reliability
Permanent Magnet Generators are currently in favor for large power systems. However:
• Weight is very high
Existing Wind Turbine Drivetrains (tons)
10
Direct Drive PM generators (tons)
–
–
–
1
0
5
10
Electrical power in MW
15
20
Iron based machines
L
Large radius (~10 m)
di (~10 )
10 MW ‐> mass over 300 tons
• Require large starting torque
A different technology platform is required …
3
Weight in metriic tons
1000
www.magnetlab.com
16 of 41
Outline
Introduction
Off Sh
Off‐Shore wind power generation
i d
ti
Current technology
Superconducting generators
gy
Technology trade‐offs
Application to off‐shore wind
Ongoing projects
Ongoing projects
Conclusion
3
•
•
•
•
•
•
•
•
www.magnetlab.com
17 of 41
Facts about Superconducting Machines
Rotor winding
•
Backiron
Superconductors operate at cryogenic temperature (below ‐200C)
– Require thermal insulation
– Require active cooling
l
•
Superconductors exhibit a non measureable electrical resistivity
measureable electrical resistivity
– free “amp. turns”
– Iron core can be removed, no saturation, less weight
– High current density
High current density
– Higher flux density possible
3-phase stator
(Copper – air core)
Superconductors exhibit AC losses in p
variable field and current
– Requires large cooling power
– Usually not used in AC components
3
•
www.magnetlab.com
18 of 41
Partially and Fully Superconducting Machines
Apparent Power output of an electrical generator:
S  B K s  r La
0
r
Partially Superconducting (PSc)
SS = apparent power (VA)
apparent power (VA)
0
Br = no‐load excitation field (T)
Ks = electrical loading (A/m)
R0 = average radius of armature
winding (m)
La = active length (m)
= angular frequency (rd/s)
p = number of pole pairs
Rotor contribution
Limited by conductor performance.
pe
o a ce.
More conductor needed in PSc because of the large air gap
2
0

p
Active volume
Larger radius needed
Larger radius needed for PSc because of the limited electrical loading
ib i
Stator contribution
Much higher values obtained in FSc because of high current density in p
superconductor
Rotation speed
i
d
Frequency needs to be kept low in FSc to limit AC losses
3
Fully Superconducting (FSc) www.magnetlab.com
19 of 41
Scaling of Sc. Machines
Typically, conventional machines scale almost linearly l
t li
l
with the power
S M hi
Sc. Machines very interesting for high torque applications
i t
ti f hi h t
li ti
20
3
www.magnetlab.com
20 of 41
Possible Configurations – Partially Superconducting
• Partially Superconducting Generator (PSG)
– High number of poles
– Superconducting rotor
d i
• Low cooling requirements
– Air
Air‐core
core stator winding
stator winding
• Resistive losses limit electrical loading
– Large “air gap”
Photos from Siemens and AMSC
• cryostat between stator and rotor
• High peak field
– Large
Large Lorentz
Lorentz
forces on HTS
coils
3
www.magnetlab.com
21 of 41
Possible Configurations – Fully Superconducting
• Fully superconducting Generator (FSG)
– High cooling requirements
• AC losses in stator
– Very high specific torque
• High electrical loading
High electrical loading
– Low number of poles
• Need low frequency for low losses
– Large Lorentz forces
• Need reliable conductor stabilization
– Torque transfer at “small” radius
Torque transfer at “small” radius
• Large conduction heat leak
CNC manufacturing
f t i off 1200mm
1200
diameter, six pole Double-Helix™ rotor
coil
3
www.magnetlab.com
22 of 41
Outline
Introduction
Off Sh
Off‐Shore wind power generation
i d
ti
Current technology
Superconducting generators
gy
Technology trade‐offs
Application to off‐shore wind
Ongoing projects
Ongoing projects
Conclusion
3
•
•
•
•
•
•
•
•
www.magnetlab.com
23 of 41
Choice of Conductor
•
The conductor defines the operating temperature of the system
•
y
p
Key conductor parameters :
– Engineering critical current density @ operating field
– Filament size
– Ratio superconductor/ non superconductor
Ratio superconductor/ non superconductor
– Minimum quench energy
– Normal zone propagation velocity
– Minimum bending radius
– Cost
YBCO conductors
• Layer configuration
• Resistive inter-layer interfaces
• Operation at 55-77 K
3
NbTi conductors
• Cu matrix
• Excellent
E ll current sharing
h i
• Operation at or below 4.2 K
BiSrCaCuO conductors
• Silver matrix
• Operation at 25-35 K
www.magnetlab.com
24 of 41
Available Conductors
6
10
2
)
JcE (A/
(A/cm
Cables
5
10
Current leads
For magnets
Transformers
Motors
&
Generators
4
10
3
Fault
Current
Limiter
Copper @50K
Superg
Conducting
Energy
storage
MgB2
@ 20K
BiSrCaCuO
Tape @ 77K
10
0
1
• 3 possible conductors
2
BiSrCaCuO
p @ 30 K
Tape
3
YBCO
Tape
@ 50K
B (Tesla)
– YBCO, Bi2223 – tape (limited to racetrack winding)
– MgB2 – tape and round wire
tape and round wire
3
www.magnetlab.com
25 of 41
High Level Conductors Comparison
1G (BSCCO) 
2G (YBCO)
2G (YBCO)

MgB2

 
 




• The choice of conductor is done at the system level considering the total cost of system
conductor-cooling system
• MgB2 is very promising:
• Price point of MgB2 moving towards $20/kAm @ 2T, 20 K
• Development of high filament count conductors (~10 m)
• 2G (YBCO) is improving fast:
• Current price point of YBCO at $500/kAm @ 2T, 60 K
• Active development towards cost reduction and multi-filaments
3
www.magnetlab.com
26 of 41
Cryocooler Applications and Operating Regions
FSG
PSG
From Ray Radebaugh, NIST
3
www.magnetlab.com
27 of 41
Comparison of Different Types of Cryocoolers
Type of Cooler
Advantages
Disadvantages
Gifford‐McMahon
High reliability (1‐3 yrs)
Moderate cost
Good service
d
Over 20,000/yr made
Large and heavy
Intrinsic vibration from displacer
Low efficiency
ff
Stirling
High efficiency
Moderate cost
Small si e and eight
Small size and weight
Over 140,000 made to date
Dry or no lubrication
Intrinsic vibration from displacer
L
Long lifetime expensive (3‐10 yrs)
lif ti
i (3 10 )
Pulse Tube Highest cryocooler efficiency for 40 Short history (OPTR since 1984)
K<T<200 K
Gravity‐induced convective No cold moving parts
instability
No cold moving parts
•Higher reliability
Lower limit to size for efficient •Lower vibration and EMI
pulse tube
•Lower cost
Steady flow (low vibration, turbo‐
expander
Long lifetime (gas bearings, turbo system)
Transport cold long distance
Good efficiency except in small
Good efficiency except in small sizes
Difficult to miniaturize
Requires large heat exchanger
Expensive to fabricate
From Ray Radebaugh, NIST
3
y
Brayton
www.magnetlab.com
28 of 41
Outline
Introduction
Off Sh
Off‐Shore wind power generation
i d
ti
Current technology
Superconducting generators
gy
Technology trade‐offs
Application to off‐shore wind
Ongoing projects
Ongoing projects
Conclusion
3
•
•
•
•
•
•
•
•
www.magnetlab.com
29 of 41
Next Generation Generator Requirements
Superconducting Machines
Direct drive – large torque
Scale very well
Lightweight High specific torque
Reliable/Robust
l bl / b
No thermal cycling, stable –
h
l
l
bl need d
more data/experience
Efficient
Low losses, high efficiency at power output
fractional power output
Low maintenance
No gearbox, sealed system, no brushes
Low cost
Competitive at high power
3
Requirement
www.magnetlab.com
30 of 41
Challenges
•
Economic
–
–
–
–
•
•
Low cost conductors
Low cost cryocoolers
Superconductor availability
Cost effective manufacturing
– Heat leaks need to be minimized
• Conduction through shaft
• Current leads
• Splices
Mechanical
– Torque transmission/torque tube
• 10s MNm to be transferred (fault)
– Large Lorentz forces (peak field >4 T)
– Torque and forces applied on conductors
Thermal
•
– Multifilament conductors
Stability
– Quench detection/protection
– Fault current/torque
MgB2 conductor
2G conductor
Carbon fiber composite thermal conductivity
3
www.magnetlab.com
31 of 41
Thermal Insulation and Torque Transmission
Shaft sees a very large thermal gradient
• Shaft sees a very large thermal gradient
• Torque tube needed to transfer torque to room temperature
– Because of turbine rotor inertia, the full fault torque needs to be transferred
– Design trade‐off between structural and thermal
Temperature
Layers of ceramics or Fiber glass
composite
p
to thermally
y insulate the
shaft end
Photo courtesy of AMSC
3
Von Mises Stress
www.magnetlab.com
32 of 41
Losses in Superconducting Machines
In Superconducting Machines, losses are almost independent from the load
Type of losses
Depending variables
Comments
AC losses
Rotor current leads
Frequency (RPM) (f and f2) AC Losses are manageable using current MgB2 conductors at Excitation field
very low frequency (low RPM low number of poles)
Excitation current
MgB2 allows for the use of a flux pump for lower losses
Stator current leads
p
Output current
Radiations
External temperature
In the case of a FSG, the stator could be connected to a f
,
superconducting transformer directly
Might require an active thermal shield (2‐stage cryocooler)
Windage
RPM
Negligible at low RPM
Conduction (torque tube)
External temperature
Iron losses
Frequency (RPM)
Excitation field
Largest heat load, present even when machine not in
operation
Negligible at low frequency
• Electrical power is needed to keep the superconducting generator cold even if no power is generated from wind. Parasitic losses are present even if the turbine is not rotating
• Parasitic losses are present even if the turbine is not rotating.
3
www.magnetlab.com
33 of 41
Electromagnetic Analysis – Stator AC losses
AC losses estimation in stator is challenging
Flux density distribution in the
stator windings
2.5
Stator
2
Norm B (T)
1.5
B
1
Current and field with
different phase angle
depending on position
of conductor
0.5
0
0.69
0.71
0.73
0.75
0.77
0.79
Radius (m)
( )
Flux density in superconducting stator for AC losses calculation
3
www.magnetlab.com
34 of 41
AC Losses and Machine Mass
• AC losses can be reduced at the expense of additional weight
• Cryocooler represents a small fraction of the total weight
350
3.50%
300
3.00%
250
2.50%
200
2 00%
2.00%
150
1.50%
100
1.00%
50
0.50%
0
0.00%
100
200
300
400
500
600
700
AC losses (W @ 20 K)
3
0
cryocooler weight (% of total m
mass)
Gen
nerator Weight ((metric tons)
Machine weight vs. AC losses in stator
www.magnetlab.com
35 of 41
Efficiency vs. RPM
• Assumptions
– Cooling system operating at 15 % of Carnot
• Efficiency remains very high at low power output
3
www.magnetlab.com
36 of 41
Machine Dynamics
• Small synchronous reactance
• Small load angle
• Very high dynamic response
• Very high stability
• Possibility of overloading
• Small variations of excitation current needed for power factor control
Short‐circuit power
• Fully‐superconducting, xd~0.2 p.u
‐> large short circuit power/torque
• Partially superconducting, xd ~0.5 – 1 p.u. ‐> Superconducting stator acts as current limiter, thus limiting the Superconducting stator acts as current limiter, thus limiting the
short circuit torque (frequency ~1Hz)
3
•
www.magnetlab.com
37 of 41
Cost consideration
• A 10 MW, 10 RPM generator requires a very large amount of conductors (10s of km)
– Cost of system conductor‐cryocooler is dominated by conductor
• Low cost conductor is the best option
• Drivetrain mass reduction Drivetrain mass reduction ‐>> lower capital and installation cost
lower capital and installation cost
– Foundations, Tower, Crane…
Wound Coil & Gearbox
Generators
• Higher efficiency and reliability
• Cost
Cost of Energy estimation shows
of Energy estimation shows
very promising results
Permanent Magnet
Generator
cost per kWh
– More energy produced
– Less down time
Fully Superconducting
Generator
– Large Sc. Generator would lead to
a lower $/kWh
l
$/kWh
2
3
4
5
6
7
8
9
10
11
12 13 14
Wind Turbine Rated Power (MWatt)
3
1
www.magnetlab.com
38 of 41
Outline
Introduction
Off Sh
Off‐Shore wind power generation
i d
ti
Current technology
Superconducting generators
gy
Technology trade‐offs
Application to off‐shore wind
Ongoing projects
Ongoing projects
Conclusion
3
•
•
•
•
•
•
•
•
www.magnetlab.com
39 of 41
Ongoing Projects
• Some superconducting wind generators ongoing projects
– Converteam/Zenergy
• 8 MW
• 12 RPM
• Partially superconducting 2G
– American Superconductor/TECO Westinghouse
Converteam/Zenergy
• 10 MW
• 10 RPM
• Partially superconducting 2G
– AML Energy
• 10 MW
10 MW
• 10 RPM
• Fully superconducting MgB2
AML Energy
‐ Others
3
www.magnetlab.com
40 of 41
Conclusion
•
Weight in metric tons
– Mass is a key design parameter and conventional machines cannot compete
PSG ~150 tons
FSG ~80 tons
100
•
Large turbines with low drivetrain mass, high efficiency and low maintenance needs will lead to significant Cost of Energy reduction
f
f
d
•
It is likely that wind power generation will become the first ll b
h f
market for superconducting generators
Existing Wind Turbine
Drivetrains (tons)
10
Direct Drive PM
generators (tons)
1
0
5
10
Electrical power in MW
15
20
HTS machines present a strong value proposition for large direct drive wind turbine generators
g
3
1000
www.magnetlab.com
41 of 41