Minimising the Usage of Superconducting Tape in Electrical Machine Applications

Minimising the Usage of Superconducting Tape in Electrical Machine ApplicationsBogi B. Jensen1, Nenad Mijatovic1, Asger B. Abrahamsen2, Chresten Træholt11 Department of Electrical Engineering, Technical University of Denmark, Denmark2 Department of Material Science – National Laboratory for Sustainable Energy RISØ, Denmark

24-10-2011SOWiT 2011 Rome, Italy

2 DTU Electrical Engineering, Technical University of Denmark

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)

http://www.timeshighereducation.co.uk/story.asp?storyCode=414302&sectioncode=26


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.


Wind Turbine Trend

“Danish Concept”DFIG

Full Converter (PM or other)

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.


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


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 5-25 years

• There is Dysprosium in Canada, Australia and South Africa, but when will these mines start production and at what cost?


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


1mR = 0.27mR-B-Fe 2RE usage in an HTS machine depends heavily on the topology

Drivetrain comparison – Rare earth usageCu&Fe

PM HTS

Geared0 25kgR/MW1

Have not been

proposedHybrid

0 60kgR/MW1 25gR/MW2

Direct drive0 250kgR/MW1 100gR/MW2


Why use Multi-Pole Generators?• The converter is indifferent

(to a certain extent)

• Power is independent ofpole numbers

• Voltage is independentof pole numbers

• Traditionally: weight (and cost) savings!

Source: www.avantis-energy.com

http://www.avantis-energy.com/


Core Back Thickness• The flux path is from one pole to the next.

cbacbcbcb dlBAB ˆ2ˆ2ˆ

pd rotorcb

1,

pd statorcb

1,


PM Direct Drive Generator

• The mass of the nacelle can be significantly reduced

2 Poles 10 Poles


End windings• Copper and HTS end winding length is reduced

2 Pole Multi-Pole

Source: www.mandc.co.za

http://www.mandc.co.za/


Multipole HTS wind turbine generator

Source: H. Ohsaki et al. “Electromagnetic Characteristics of 10 MW Class Superconducting Wind Turbine Generators”, ICEMS, 2010.


Mass, HTS length and price as a function of pole number


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


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!


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


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.


Armature• A 2 pole, 22kW induction machine• ID: 160mm• Stack length: 150mm


Cryostat• Thermal insulation (300K and 77K)• Vacuum (10-5 mbar)• Multi Layer Insulation (MLI)• Effective airgap of 10mm• Torque Transfer Element• Contains the HTS winding


HTS field winding• Mounted on a core which can contain up to 10 race track coils (4mm)



HTS coils• The HTS coils are equipped with voltage measurement, temperature

sensors and Hall probes


• The superconducting state is limited by– Critical flux density Bc

– Critical current density Jc– Critical temperature Tc

• HTS materials can be characterisedby IV curves

• E0 is the electric field at the critical current (1μV/cm)

( , )

0[ / ]( , )

n B T

c

JE V m EJ B T

High Temperature Superconductors


VI curves for individual coils installed in the machine

( , )

0[ / ]( , )

n B T

c

JE V m EJ B T



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



Employing multiple power supplies

• Increased the airgap flux density by 12% without optimisation



Topology optimisation

Source: N. Mijatovic et al. “Coil Optimization for High Temperature Superconductor Machines”, IEEE Trans. Appl. Supercond., Vol. 21, No. 3, 2011.

• 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


Combining topology optimisation with multiple power supplies

Source: N. Mijatovic et al. “Coil Optimization for High Temperature Superconductor Machines”, IEEE Trans. Appl. Supercond., Vol. 21, No. 3, 2011.

• 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%


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


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).

VIND I ØRESUND

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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Minimising the Usage of Superconducting Tape in Electrical Machine Applications

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