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Winding, Fabrication, Engineering Design, and Other Considerations for 2G HTS CoilsHonghai Song, Paul Brownsey, Toru Fukushima and Drew W. Hazelton

Magnet Technology 2013 (MT-23): Session 5OrAB July 15 – 19, 2013 Boston, MA

MT‐23 Boston, MA July 15‐19, 2013All Rights Reserved. Copyright SuperPower® Inc. 2013

Acknowledgement

• Many thanks to my colleagues at SuperPower for their support, assistance and helpful discussions

– M. Albertini– L.V. Hope– E.L. Keehan– A.R. Knoll– T.F. Lehner– E.S. Lord– R.B. McClure– R. Pasquini– S. Repnoy– H. Sakamoto– J. Waterman– Y. Zhang

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Outline

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• Introduction– 2G HTS conductors and coil winding activities

• 2G HTS coil winding– Double pancake coils

• Coil stress analysis – Winding stress – Thermal and magnetic stress

• Engineering design– In-field Ic(B, T, Φ) characterization– Coil design considerations

• Other technical developments – Terminal leads and joints– Insulation and epoxy

• Summary


SuperPower focus: 2G HTS wire and coils

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• Second‐Generation High‐Temperature Superconductor wire– Produced in kilometer‐class lengths– World‐leading performance

achievements at all piece lengths– Robust wire characteristics– Produced in multiple device‐specific

configurations – Suitable for a wide variety of

applications: energy, industrial, science & research, military & defense, transportation, space, healthcare

• 2G HTS Coils– Design, engineering, fabrication and

testing to meet your needs


2G HTS conductor production at SuperPower

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1) Substrate electro-polishing 3) REBCO layer MOCVD2) IBAD-MgO

5) Production Ic testing

4) Various width conductors(3, 4, 6, and 12 mm wide)

• Hastelloy Substrate provides mechanical strength • IBAD-MgO provides template for growing epitaxial buffer layers• Thin, flexible and robust conductors

(1)

(2)(3)

(4)


2G HTS coil winding: double pancake coils

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SS spool

Conductor spool

Alignmentbeam

Windingrollers

Winder

• Positioning critical with good tension control• Pre-alignment for initial turns

Epoxy applied after the winding

• No winding guide wall, • Roller close to coil body


Partial epoxy application on coil sides

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• Very thin layer of epoxy (transparent) after epoxy is cured

• Mechanical fix turn-turn and layer-layer

• Provides thermal link between optional cooling plates and windings

• Seals the coil

-2.00E-03

0.00E+00

2.00E-03

4.00E-03

6.00E-03

8.00E-03

1.00E-02

0 10 20 30 40 50

Vol

tage

(V)

Current (A)

TC#1

TC#2

TC#3

TC#4

TC#5

Five thermal cycles (77K), no degradation found


Use of co-wound stainless steel as “insulation”• Mechanical, Mitigates radial tensile stress on the 2G

HTS, so Improves overall coil strength

• Thermal, higher thermal conductivity

• Electrical– In SS co-wound coils, ss strip plays as insulator

while superconductor is in superconducting state,

– but as superconductor turns into normal state, particularly during quenching, current will be redistributed into neighboring turns, through turn-to-turn contact

– HTS Quench induced V? (May not be that high as in LTS!)

• LTS: RQ = Rnz, ~Ω, high voltage, millisecond • HTS: RQ = Rturns + Rnz, ~mΩ, a few seconds

– If such turn-to-turn contact is well adjusted (depend on turn-to-turn stress), it may generate manageable amount of Joule heat, so as to enhance overall quench propagation.

8

1

1δ =?

LTS:

HTS:

<1

[Wilson]


Winding tension impacts residual coil stress in windings (hoop & radial)

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• Analytical calculation of winding stress based on 4’’ diameter pancake coil• Be able to optimize winding induced tension in wound coils by changing

winding tension– Back tension motor control, 10%, 20%, 30%, 40%, 50%, 60%, 70%– Resulted winding tension 6.9 MPa, 13.8 MPa, 20.7 MPa, 27.6 MPa, 34.5 MPa,

41.4 MPa, 48.3 MPa

-9

-8

-7

-6

-5

-4

-3

-2

-1

00.5 0.6 0.7 0.8 0.9 1 1.1

Rad

ial S

tres

s σr

(MPa

)

r/b

6.9 MPa

13.8 MPa

20.7 MPa

27.6 MPa

34.5 MPa

41.4 MPa

48.3 MPa

Hoop stress Radial stress

compression

tension

MT‐23 Boston, MA July 15‐19, 2013All Rights Reserved. Copyright SuperPower® Inc. 2013 10

• 2D axisymmetric modeling• 4’’ diameter pancake coil, 1’’ radial build-up, 175 turns• SS co-winding, no epoxy, No PET release layer in modeling,

Radial stress edge concentration near ID, max is < 2.6 MPaMaximum displacement is on OD, ~0.36 mm

If replaced by PET Release layer, Reduce stress on wound conductors, particularly the first few turns. That’s what we did!

Thermal stress due to cool-down (from RT to 77 K)

Former Coil


Magnetic strain and stress in 4’’ test coil

eR, 0.0045% eZ, 0.0025% ePhi, 0.0005%

But yielding strain, ~0.5%[W.D. Markiewicz et al. IEEE TAS, 22(3), 2012]

Magnetic stress (edge, PC)significantly increases with current

1000A

ʘIop=100 A Iop=100 A Iop=100 Acompression

tension


A typical magnet design: field B vs Iop/Ic

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0

5000

10000

15000

20000

25000

30000

0 10 20 30 40 50 60 70 80 90

Btot (G

auss)

Field angle from ab plane (Degree)

A 2 T Helmholtz split magnet @ 65K, Iop = 52AL1

L2

L3

L4

L5

L6

L7

L8

L9

L10

L11

L12

L13

L14

L15

L16

L17

L18

L19

L20

Lowest Iop/Ic at magnet edge, ~20° (weakest point)

Btot vs Φ (field angle from ab plane ) across magnet cross-section

Line #Outeredge

Axialcenterin Coil


Ic(B,T, Φ) characterization is in high demand

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Measurements made at the University of Houston

• Lift factor, Ic(B,T)/Ic(sf, 77K), particularly a full matrix of Ic(B,T, Φ) is in high demand.• Frequently sought by coil/magnet design engineer, for various applications.• Used to calculate local Iop/Ic ratio inside coil body, and design quench protection.

0

1

2

3

4

5

6

7

0.0 2.0 4.0 6.0 8.0 10.0

Lift Factor [ Ic(H,T)/Ic(sf, T) ] //ab

Applied Field (Tesla)

M3‐909‐3 Lift Factor vs. H//ab, T65 K 50K 40 K 30K 20K

0

1

2

3

4

5

6

7

0.0 2.0 4.0 6.0 8.0 10.0Lift Factor [ Ic(H,T)/Ic(sf, T) ] //ab

Applied Field (Tesla)

M3‐909‐3 Lift Factor vs. H//c, T65 K 50K 40 K 30K 20K


Terminal leads, joint, transition

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• Terminals and leads are potential sources of damage in 2G HTS coils• Consequently, their design, handling and fabrication are very critical• Lessons learned: Avoid kinking or overbending, rather make smooth

transition

Cu base for terminals and joints (FLAT leading in and out)

Bridge joints between pancakes, Rtot = 10-7Ω

Smooth transition in between two pancake coils


Recent fully wet coil winding is promising • Design of experiments on Adraldite™ epoxy mixed with Alumina

– Epoxy (Araldite DBF): hardener (Araldite 951) = 10:1 • Mixed Epoxy : Alumna powder = 3:2 out of (4:1; 3:1; 3:2 ; 1:1)

– Significant amount of bubbles found degas process will help– Drop cured-epoxy into LN2, no breaks at all fully wet coil winding

• A fully wet wound coil– No additional insulation except for the epoxy

• Two thermal cycles, no degradation found– Compared to coils with stainless steel co-winding

• No major difference found in static Ic measurement

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‐4.0E‐7

‐2.0E‐7

0.0E+0

2.0E‐7

4.0E‐7

6.0E‐7

8.0E‐7

1.0E‐6

1.2E‐6

1.4E‐6

0 10 20 30 40 50

ETE Vo

ltage

(V)

Current (A)Dry coil Fully Wet coil

• Full wet winding, PC, 10m• Partial epoxy & SS, DPC, 140m

[C Barth et al, KIT, SuST. 26 (2013) 055007]


A case summary for a successfully developed magnet system

• Module #1:In-coil splices, 17.2 nΩ and 9.9 nΩ in DPC#1; 14.2 nΩ and 15.2 nΩ in DPC#2DPC#1, Ic = 37.6A, n-value = 20.4DPC#2, Ic = 42.8A, n-value = 21.8Module Ic = 32.8A, n-value = 22.1 Superconductor bridge joint resistance, R = 100 nΩ

• Module #2: In-coil splices, 8.6 nΩ and 7.6 nΩ in DPC#3; 17.5 nΩ and 10.0 nΩ in DPC#4DPC#3, Ic = 38.8A, n-value = 23.8DPC#4, Ic = 36.3A, n-value = 20.9Module Ic = 32.0A, n-value = 19.6Superconductor bridge joint resistance, R = 60 nΩ

• Module #3: In-coil splices, 12.5 nΩ and 8.5 nΩ in DPC#5; 10.5 nΩ and 12.5 nΩ in DPC#6DPC#5, Ic = 45.5A, n-value = 24.2DPC#6, Ic = 50.6A, n-value = 25.5Module Ic = 42.0A, n-value = 25.6 Superconductor bridge joint resistance, R = 70-80 nΩ

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Including three modules of six double pancake coils, total length 840 m - a proven successful development.


Summary• Successful demonstration with high quality 2G HTS coils

– Use of co-wound stainless steel as “insulation” with partial epoxy application on coil sides• Stress calculation analysis

– Winding stress• Both conductor positioning and tension control are critical

– Thermal stress due to cool-down• PET release in former:coil

– Magnetic stress• Less than winding stress at low current, magnetic tension lower than yielding point• But may become dominant when I>1000A, particularly for high field insert magnet

– Stainless steel co-winding• Likely improves overall coil stability and quench behaviors• Accumulated stress further impacts turn-to-turn resistance/conduction• More experiments are needed to quantify relationship between turn-to-turn pressure and quench

behaviors• Coil terminals and joints

– Avoid kinking and over bending, and making smooth transition• Fully wet winding where conductors needs to be well supported, to handle local thermal stress

– Fully wet coil winding development is on-going– Several epoxy/insulation options are very promising

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Questions?

Thank you for your interest!

For further information about SuperPower, please visit us at: www.superpower-inc.com

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