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Outline

• Motivation for off-shore wind?

• Double-Helix winding

• Fully superconducting generator

• Scaling

• Cost consideration


Source: US Department of Energy, 20% Wind Scenario

• Wind is on track to provide 20% (300 GWatts) of the total US electricity consumption by 2030.

• Large, offshore wind turbines will generate over 15% of this electricity

2009 2030

20 GWatts

300 GWatts

250 GWatts

1 GWatt powers about 300,000 homes

• Offshore wind turbines generate more power than on-shore turbines

because wind speeds are generally higher and the wind is steadier offshore.

• Larger turbines up to 160 m in diameter, which can

capture more wind energy, are feasible offshore

since transportation logistics are possible via water.

• Power can be generated near large population centers with shorter

transmission lines to load centers, resulting in lower costs.

Wind Power – growing and moving offshore

US Wind Growth Scenario• Larger turbines lead to lower cost production

of electricity i.e. more kWh are generated per

capital equipment dollars spent.

Benefits of offshore …


Offshore Wind – poised for growth

Over the next 5 years Offshore Wind will be a significant

component of the US Renewable Energy spectrum

Over the next 5 years Offshore Wind will be a significant

component of the US Renewable Energy spectrum

• A solid experience base exists with European offshore windfarms in existence since 1991. European offshore

windfarms are generating 1,100 MWatts with 70-90% availability. Deep water offshore is progressing.

• Historically, in the US, regulation and politics have slowed the deployment of offshore wind. However, the new

administration is very proactive in promoting development of offshore wind.

• Clearer policies with less red tape for offshore

property leases have been established by DOI

Since January 2009:

• Department of Interior proactively promoting

offshore wind development

• Department of Energy commissioned 1 year study on

superconducting generator technologies for 10MW offshore turbines

• Portions of Federal Renewable Energy Funding and

Stimulus are being directed to offshore wind

“U.S. offshore areas hold enormous potential for wind energy

development near the nation’s highest areas of electricity

demand – coastal metropolitan centers … the wind potential

off the coasts of the lower 48 states actually exceeds our entire

U.S. electricity demand” Secretary of the Interior - Ken Salazar

• Cape Wind, the first offshore wind farm in US, receives

unanimous permit approval in Massachusetts

DOE-NREL

deep


Large Wind Generators

1

10

100

1000

0 5 10 15 20

We

igh

t in

me

tric

to

ns

Electrical power in MW

Existing Wind Turbine

Drivetrains (tons)

Direct Drive PM

generators (tons)

A different technology platform is required …

• Sizes > 10+ MW @ 10 RPM

• No gearbox > higher reliability

• Weight is very high

– Iron based machines

– Large radius

– 10 MW weight over 300 tons

• Require large starting torque

Large wind turbines are desired for offshore

deployment. Lightweight, reliable generators

are paramount to the economic feasibility of

such systems.

Permanent Magnet Generators are currently in

favor for large power systems. However:


Electro-Magnetic Packaging - robust, reliable, optimized

Racetrack Coils Double-Helix™ Coils

Electro-Magnet

Packaging Technology

DH Geometry -

Embedded Conductor

DH Geometry -

Embedded Conductor

Turns and

Stacked Layers

Turns and

Stacked Layers

• Low Harmonics - Efficient

• Robust – Handles High Forces /Torque

• Less Splices – More Reliable

• Optimal for Superconductors

• Automated Manufacturing


• Conductor is mechanically stabilized… providing intrinsic

force management

• Conductor is placed precisely where designer intended it

… yielding a high design “fidelity”

• Any number of magnetic “poles”, with one continuous

winding (splice-free)

• Harmonic-free fields with sinusoidal pole transitions –

“Pure Fields”

• Automated manufacturing

Enabling Features & Benefits

Six Pole

Six Pole

Flared

Two Pole

Twisted

Bent & Combined Function


Double-Helix in Superconducting Rotating Machinery

High Reliability/Robustness

• Pure field: no vibrations

• Outstanding conductor stabilization

• Distributed structural containment

• Improved quench propagation (winding

spreads in different direction)

• Winding is self protected against quench when

using MgB2

• Excitation using AML’s flux pump technology

• Splice free multi-pole rotor

High Specific Torque/Power

• High air gap flux density

• No iron core in the rotor

• Outstanding mechanical torque transfer

• Number of poles not limited by radius

• Superior dynamic capabilities

Partially Superconducting Generator

Double-Helix Fully Superconducting Generator

Backiron

Rotor Superconducting

DH winding

3-phase Superconducting Armature


Generator in Turbine Nacelle

Double-Helix ™ Stator ��

Double-Helix™ Rotor ��

Input Shaft (no gearbox) ��

Cooling Gas Inlet ��

Rotor Excitation System ��

Backiron and Cryostat ��

• 10 MWatt Power at 10 RPM

• 5 meters long, 2.9 meter diameter

• ~70 tons total weight (1 ton = 1,000 kg)

• 9.6 MNm rotor torque

• Operates at temperature of 20K

• 10 MWatt Power at 10 RPM

• 5 meters long, 2.9 meter diameter

• ~70 tons total weight (1 ton = 1,000 kg)

• 9.6 MNm rotor torque

• Operates at temperature of 20K


Choice of Conductor

• The conductor defines the operating temperature of the system

• Key conductor parameters :

– Engineering critical current density @ operating field

– Filament size

– Ratio superconductor/ non superconductor

– Minimum quench energy

– Normal zone propagation velocity

– Minimum bending radius

– Cost

NbTi conductors

• Cu matrix

• Excellent current sharing

• Operation at or below 4.2 K

BiSrCaCuO conductors

• Silver matrix

• Decent current sharing

• Operation at 25-35 K

YBCO conductors

• Layer configuration

• Poor current sharing

• Operation at 55-77 K


Why MgB2 is the Right Conductor Choice…

1G (BSCCO)

2G (YBCO)

MgB2

�

�

�

�

� �

�

• Even though operating temperature is lower, advantages of MgB2 in other areas outweigh

cooling impact.

• Much more development $$$ have gone into 1G and 2G; potential for continuous

performance improvement of MgB2 is much higher than for other conductors.

• Price point of MgB2 moving towards <$2/kAm.


• Ultra-High Reliability and Low Maintenance

– Turbo-Brayton cryocoolers utilize miniature high-speed turbo-machines that operate in gas film or magnetic

bearings.

• High Cooling Capacity and Multiple Cooling Stages

– Cooling capacities of 1 kW (@ 20K) and above are easily achievable and have been previously demonstrated.

• Distributed Cooling with no Additional Cryogenic Circulator

– The reverse-Brayton cycle inherently provides the ability for distributed cooling.

• Flexible Packaging (Including HTS Machine On-Shaft Mounting)

– The reverse-Brayton cycle allows for very flexible packaging, even including within the shaft of a rotating

machine such as an HTS wind turbine generator.

Reversed Turbo Brayton Cycle Cryocoolers


DH Fully Superconducting Generator Preliminary Design

AC losses ~350 W;

Losses are estimated based on published regressions of experimental data. Fairly sophisticated

models exist, however, the losses in AC armatures may be overestimated and will be

experimentally determined.

Calculated Machine Parameters

Design Outputs Nominal Speed (RPM) 10

Power (kW) 10,000 Operating Temp. (K) 20

Torque (Nm) 9.5 MNm Machine mass

Efficiency (%) 99.5 Total weight (kg) 73,500

Nb. Of poles 6 Specific torque (Nm/kg) 141

Frequency (Hz) 0.5 Electromagnetic parameters

Overall Dimensions No-load field (T) 1.2

Rotor OD (m) 1.9 Synchronous reactance

(p.u.)

0.8

Machine OD (m) 2.5 Electrical loading (kA/m) 600

Length (m) 5.5 Cryo -losses (W @ 20 K) ~600


Rotor/Stator

Stator

Rotor

Input torque

Static

anti-torque

plate

Vacuum gap

Outer cryo wall

Iron


Heat Load Summary

• Shafts conduction losses are calculated assuming G10. Losses can be

reduced by combining several material

• Current leads losses are calculated assuming conduction cooled copper

leads. Losses can be decreased by considering different materials

• AC losses calculation assumes 20 micron-filaments. 10 micron-filaments

should be available within the next few years.

Component Estimated heat load (W)

Shaft torque tube (20-300 K) ~ 30

Armature torque system (20-300 K) ~ 30

AC losses ~ 500

Current leads ~ 150

Thermal gradient


Cross-section of 3-Phase Stator

-800 -600 -400 -200 0 200 400 600 800

-500

-400

-300

-200

-100

0

100

200

300

400

500

Y-Axis [mm]

Z-A

xis

[m

m]

2-pair DH windings for each phase

The layers composing the 3-phase system are optimized in terms of number of

turns, amplitude modulation and location to achieve a balanced system

3-phase system


Electromagnetic Analysis - Stator

• DH winding represented by

1 layer per phase with

sinusoidal current density

Back iron

3-phase DH winding

• The fields from each phase DH winding

add up to create multi-pole field

distribution.

• Time variation of the phase current

will lead to field rotation.

• 3 layers (3 phases)

with a 2*π/3 angular

shift


• ~1.2 T in the air gap

• Peak field validated

Electromagnetic Analysis – Rotor

• Peak field in the rotor can be

adjusted through the spacing of

the layers

• Winding optimization is

performed with CoilCad™


Conductor Operating Points

• Design based on current

conductor technology

• Rotor design requires high

Jc at 2-3T

• 20 % margin considered

for the rotor

• Stator conductor operates

at lower field

• Stator conductor requires

lower Jc and must exhibit

low AC losses

Stator and Rotor conductors can be custom designed to improve performanceStator and Rotor conductors can be custom designed to improve performance

0

200

400

600

800

1000

1200

1 1.5 2 2.5 3 3.5

Cu

rre

nt

de

nsi

ty (A

/mm

2)

Flux density (T)

Critical curent density - Columbus Superconductor current data

Rotor load line

Stator load line

0

200

400

600

800

1000

1200

1 1.5 2 2.5 3 3.5

Cu

rre

nt

de

nsi

ty (A

/mm

2)

Flux density (T)

Critical curent density - Columbus Superconductor current data

Rotor load line

Stator load line

Stator Operating area

Rotor Operating area


Force Distribution in the Conductors

EM torque

Distributed in

dense current areasRotor “self”

Lorentz Forces

Applied on innermost layer

Lorentz forces are contained through the tension of the windings and through

mechanical, layer-based stabilization of the conductors.


Electromagnetic Analysis – Stator AC losses

0

0.5

1

1.5

2

2.5

0.69 0.71 0.73 0.75 0.77 0.79

No

rm B

(T

)

Radius (m)

B

Stator

Flux density in superconducting stator for AC losses calculation

Flux density distribution in the

stator windings

Losses are acceptable

with current conductor

technology (~25 µµµµm

filaments).

They will be further

decrease as filament size

decreases


Efficiency vs. RPM

• Assumptions

– Cooling system operating at 15 % of Carnot

98.60%

98.70%

98.80%

98.90%

99.00%

99.10%

99.20%

99.30%

99.40%

99.50%

99.60%

0 2 4 6 8 10 12

Eff

icie

ncy

at

Ma

x T

orq

ue

(%

)

RPM

Efficiency (%) vs. RPM for Max. Torque


0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

3.00%

3.50%

0

50

100

150

200

250

300

350

0 100 200 300 400 500 600 700

Ge

ne

rato

r W

eig

ht

(me

tric

to

ns)

AC losses (W @ 20 K)

Machine weight vs. AC losses in stator

cryo

coo

ler w

eig

ht (%

of to

tal m

ass)

0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

3.00%

3.50%

0

50

100

150

200

250

300

350

0 100 200 300 400 500 600 700

Ge

ne

rato

r W

eig

ht

(me

tric

to

ns)

AC losses (W @ 20 K)

Machine weight vs. AC losses in stator

cryo

coo

ler w

eig

ht (%

of to

tal m

ass)

• AC losses can be reduced at the expense of additional weight

• Cryocooler represents a small fraction of the total weight

Preliminary Sizing Trade-offs


Integrated Transformer Concept

• Required because

of the low

frequency

• Small footprint

• Very low losses

(low voltage is

superconducting)

• Shares the machine

cryostat

• No current leads

• Transformer can act

as current limiter

• More flexibility on

machine design

Main Shaft (15 RPM)

TransformerSuperconducting primary

Normal conducting

secondary

Stator (Superconducting)

Cryostat (@ 15-20K)

PowerConversion

(AC-DC-AC)

SystemControls

CryocoolingSystem

Rotor

Excitation

(Superconducting)

Power Out ��

Power In ��

Back Iron


Double Helix Fully Superconducting Generators

1

10

100

1000

0 5 10 15 20

We

igh

t in

me

tric

to

ns

Electrical power in MW

Existing Wind Turbine Drivetrains (tons)

Direct Drive PM generators (tons)

DH-MgB2_Weight (tons)

• Fully Superconducting– No iron core

– High current density

– Large electrical loading

– High torque density

• Double-Helix™ Technology – Harmonics free air gap flux

– Conductor stabilization

– Electrical insulation

– Improved quench propagation

– Outstanding torque transfer

– High reliability

– Enable the use of superconductors

– Numerous cost advantages


AML Energy Generators – Less Weight �� Lower Cost of Power

• The lowest cost producers of Offshore Wind Power will be very large, 10 MWatt and greater, wind turbines.

• Current Generator Technologies will not scale up due

to excessive size and weight. System costs actually

start to increase as incremental additional weight

exceeds benefit of additional power.

• The AML Superconducting Generator

provides “game-changing” technology …

… enabling large offshore wind,

resulting in lower cost production

cost

pe

r kW

h

Wind Turbine Rated Power (MWatt)

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Wound Coil & Gearbox

Generators

Permanent Magnet

Generator

Fully Superconducting

Generator

AML Energy Fully-Superconducting

Permanent Magnet

Copper Wound-Coil

with Gearbox

10 MWatt Generator

Size Comparison

70 Tons

320 Tons

500 Tons

Partially Superconducting

150 Tons

amlcleanenergy.com 08/10masbret.com/docs/ASC2010-wind.pdfamlcleanenergy.com 08/10 Source: US...

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