2G HTS Properties Beyond Critical Current

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SuperPower Inc. is a subsidiary of Furukawa Electric Co. Ltd.

2G HTS Properties Beyond Critical Current

DW HazeltonFriday, October 11, 2013 CHATS 2013, Cambridge MA

CHATS 2013 Cambridge, MA October 11, 2013All Rights Reserved. Copyright SuperPower® Inc. 2013

Acknowledgements

2

• We would like to acknowledge the contributions of the team at SuperPower as well as collaborators from around the world.

• In particular we would like to acknowledge the input from Toru Fukushima, Paul Brownsey, Honghai Song*, Yifei Zhang, Justin Waterman, Trudy Lehner, Hisaki Sakamoto, John Dackow, Ross McClure and Allan Knoll.

• The work presented here is supported in part from funding from the US DOE Smart Grid Program and ARPA-E.

*currently at MSU-FRIB


Outline

• SuperPower 2G HTS conductor architecture• Critical current status• Mechanical properties

– General properties– Delamination

• FCL functionality• Insulation• Splices• Closing remarks

3

CHATS 2013 Cambridge, MA October 11, 2013All Rights Reserved. Copyright SuperPower® Inc. 2013 4

Wire performance critical to practical applications• Ic(B, T, )

– Temperature, magnetic field and field orientation dependence of Ic– Minimum Ic at operating condition

• Mechanical properties (electromechanical performance)– Workability for fabrication into various devices– Irreversible stress or strain limits under various stress condition, in terms

of Ic• Uniformity along length (Ic and other attributes)• Thermal properties (thermal expansion coefficient and thermal conductivity)• Quench stability (NZPV and MQE)• Insulation (material and method)• Splice

– Resistance (resistivity)– Mechanical strength (tensile and bending)


• Hastelloy® C276 substrate• high strength• high resistance• non-magnetic

• Buffer layers with IBAD-MgO • Diffusion barrier to metal substrate• Ideal lattice matching from substrate through ReBCO

• MOCVD grown ReBCO layer with BZO nanorods• Flux pinning sites for high in-field Ic

• Silver and copper stabilization

SuperPower’s ReBCO superconductor with artificial pinning structure provides a solution for demanding applications

5


Each layer serves a function….• Substrate (Hastelloy® C-276) provides mechanical strength,

electropolished base for subsequent layer growth• Buffer stack provides:

– Diffusion barrier between substrate and superconductor– IBAD MgO layer provides texture template for growing aligned

superconductor, necessary for high current density– Final buffer layer provides lattice match between buffer stack and

superconductor• HTS superconductor layer – (RE)BCO superconductor with BZO

based pinning sites for high current carrying capability in background magnetic field.

• Ag layer – provides good current transfer to HTS layer while providing ready path oxygen diffusion during final anneal.

• Cu layer – provides stabilization (parallel path) during operation and quench conditions.

6


Ic(B,T, Φ) characterization is critical to understanding the impacts of processing on operational performance

7

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 10.0

Lift 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


Ic uniformity along length (TapeStar)

8

Position (cm) (on a 12 mm wide wire)

• Magnetic, non-contact measurement• High spacial resolution, high speed, reel-to-reel• Monitoring Ic at multiple production points after MOCVD• Capability of quantitative 2D uniformity inspection


Ic uniformity along length (four-probe transport measurement)

9

Position (m) (on a 4 mm wide wire)

Ic (A

, 77K

, s.f.

) and

n-v

alue


Tensile strength predominately determined by substrate

10

Tensile stress-strain relationship of SCS4050 wires with different Cu stabilizer thickness (room temperature)

Tensile stress-strain relationship of as-polished Hastelloy substrate(room temperature)

100 µm Cu

40 µm Cu

20 µm Cu


0

200

400

600

800

1000

1200

0.000 0.002 0.004 0.006 0.008 0.010 0.012

stress (M

Pa)

strain

Copper thickness

40 µm

60 µm

100 µm

Conductor Stress‐Strain at 77K and 4 K with Various Copper Thickness

Significant softening of the stress‐strain curve with added copper due to reduced modulus and yielding of the copper.


Tensile strength - effect of stress on Ic

12

Normalized Ic vs. room temperature tensile stress for a 12mm wide wire with 100m Cu stabilizer


Tensile test of wires with SCS

13

• Measurement of baseline data• Effect of Cu/Hastelloy ratio

M3-914-1 (100µm Cu)Stress limit 460MPa

M3-861-2 (40µm Cu)Stress limit 620MPa


Axial compressive tests at BNL on pancake coil show no Ic degradation to at least 100 MPa

14

WB Sampson et al, Proceedings of 2011 Particle Accelerator Conference, New York, NY TUP169

Pancake coil fabricated from 12mm wide SP 2G HTS

Compressive Ic test setup (LN2 testing)

Typical Ic trace

Summary of Ic data on coil sections


(RE)BCO coils can be subject to degradation under thermal cycling

15

Conclusions(1) The critical current of epoxy impregnated

circular coils wound using YBCO-coated conductors can be degraded in use.

(2) Degradation occurs if the cumulative radial stress developed due to winding, cool down and Lorentz force exceeds the critical transverse stress for the YBCO coated conductor, typically +10 MPa.

(3) The YBCO conductor is fractured at the interface between the buffer layer and the YBCO layer, or at the YBCO layer itself, causing cracks on the YBCO layer resulting in significant decline of the critical current.

• Takematsu et al., Physica C 674-677, 470, 2011


Cu

REBCOBuffer

Hastelloy

Cu

Cohesive

Adhesive

Mixed mode

Ag

Ag

Delamination strength studied with peel test

16

P

T-peel test

90 peel test

P

Displacement (mm)

Pee

ling

Load

(N)

Relationship between peel strength and processing conditions established


Successful winding techniques demonstrated to mitigate delamination issue • Decoupling of former from winding has been demonstrated to be

beneficial– Eliminates radial tensile stress on the 2G HTS windings– PET release layer incorporated at former:windings interface– Lower thermal expansion formers (Ti, controlled expansion glass-

epoxy)• Alternative insulations/epoxy systems have been successfully

demonstrated– PET shrink tube - NHMFL– Electrodeposited polyimide - Riken– Alternative epoxy system with filler - KIT

• Use of cowound stainless steel as “insulation” with partial epoxy application on coil sides – Mitigates radial tensile stress on the 2G HTS – Improves overall coil strength– Negative impact on coil current density

17


Stainless steel insulation, partial epoxy application on coil sides shows resistance to delamination

18

• 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


0.0E+00

2.0E‐04

4.0E‐04

6.0E‐04

8.0E‐04

1.0E‐03

1.2E‐03

1.4E‐03

0 10 20 30 40 50

Volta

ge over 1

0 meter (V

)

Current (A)

TC#5 TC#4 TC#3 TC#2 TC#1

Alternative epoxy for wet wound coils shows resistance to delamination

• Design of experiments on Adraldite™ epoxy with Alumina– Epoxy (Araldite DBF): hardener (Araldite 951) = 10:1

• A fully wet wound coil– Conductor M3-919-2 BS, 566-576, 10 meter, 52 turns, ID=2’’– No additional insulation except for the epoxy, PET release

• Five thermal cycle, no degradation found

19

Ic=42.9A, n-value=~18

Five thermal cycles, no degradation

‐1.5E‐03

‐1.0E‐03

‐5.0E‐04

0.0E+00

5.0E‐04

1.0E‐03

1.5E‐03

2.0E‐03

0 10 20 30 40 50Volta

ge (V

)

Current (A)

200 A/min 10 A/min

In TC#5, ramp rate comparison, no difference in Ic and n-value, 42.9A/17.5

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


-100

-80

-60

-40

-20

0

20

40

60

80

0 20 40 60 80 100

Time [ms]

Cur

rent

[kA

]

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

Volta

ge a

cros

s H

TS

elem

ents

[kV]

Iprospective I_total_KEMA I_HTS Ish V_total_KEMA

-5.0-4.0

-3.0-2.0-1.00.0

1.02.03.0

4.05.0

2 4 6 8 10 12 14 16 18 20

Time [ms]

Cur

rent

[kA

]

-1.0-0.5

0.00.51.01.5

2.02.53.0

3.54.0

Volta

ge a

cros

s H

TS

elem

ents

[kV]

I_total_KEMA I_HTS Ish V_total_KEMA

Quench speed around 0.5 ms

2G Conductor for SFCL Shows Consistent, Excellent Performance

High-power SFCL test 2G

Prospective current 90 kA*

Limited current 32 kA

Peak current through element

3 kA

Response time < 1 ms

Element quality range Uniform

Fast response time


Capability for bonded conductors being developed [higher amperage, specialty applications (FCL) ]

21

• Bonded conductors offer the ability to achieve higher operating currents– LV windings of FCL transformer– HEP applications– High current bus applications

• Bonded conductors offer higher strength – FCL transformer fault currents– High field HEP applications with high force loadings

• Bonded conductors offer the ability to tailor application specific operating requirements, i.e. normal state resistance for a FCL transformer


0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0 100 200 300 400 500

resi

stan

ce /

leng

th (o

hm /

m)

temperature (K)

composite resistance / length 70Cu-30Ni

0.100 mm 0.200 mm 0.300 mm0.400 mm 0.500 mm 0.600 mm0.800 mm 1.000 mm target

12 mm wideC276 50.0 m(RE)BCO 1.0 msilver alloy 4.0 msolder 10.0 m

target

Bonded conductors meet target normal state resistance while meeting mechanical strength targets for FCL transformer application]

• DOE SMART GRID Project• 28 MVA 3-phase FCL Medium

Power Utility Transformer (69 kV / 12.47 kV class)

• Testing on So. California Edison Smart Grid site in Irvine, CA – plan min 1 year of grid operation


Insulation and other ongoing developments

• Additional wire insulation methods under development– Today: Kapton®/Polyimide wrapped (1-2 kV)– Other options under development:

thinner profile, better coverage

• Additional wire architectures under development – Higher current carrying capability

• Multi-layer combinations• Cable on Round Core (CORC)• Thinner substrates

– Custom attributes• FCL – normal state resistance feature

23

Courtesy: Advanced Conductor Technologies


Demanding requirements for ROEBEL cable for ac applications• ROEBEL cable is a known approach to produce low ac loss, high

current conductor/cable• Conductor exposed to severe mechanical cutting at sharp angles

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ROEBEL cable made by KIT with SuperPower®

2G HTS Wire

No failure, no delaminationOnly 3% loss in current from conductor to ROEBEL cableCable engineering current density = 11,300 A/cm2


Terminal leads, joint, transition

25

• Terminals and leads are potential sources of damage in 2G HTS coils• So their design, handling and fabrication are very critical• Key points: Avoid kinking or over bending, making smooth transition with adequate

support

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

Bridge joints between pancakes, Rtot=10-7Ω

Smooth transition on inner crossover


Reliable splices – low resistance and high strength

26

• Splicing / terminations required in most applications

• Splice properties are important conductor performance and have influences on dielectrics and cryogenics as well

• Low resistance and high electromechanical strength are basic requirements

• Contact resistivity at REBCO/Ag interface has an effect on splice resistance• Splices fabricated via soldering at a temperature below 250C• Soldering temperature, pressure, duration time are important parameters• Ic retained across splices with no degradation through soldering• Splice resistance R ≤ 20 n for the lap joint geometry with a 10cm overlap

length

Bridge joints between pancakes, Rtot = 10-7Ω


Splice Ic and resistance vs. bending diameter

Bending Diameter (mm)

I c(d

) / I c

(∞) o

r R(d

) / R

(∞) R

atio

• Lap joint (HTS-HTS) of SCS4050 tapes with 40 µm Cu stabilizer• R(∞) = 6 ~ 20 n with 10 cm overlap length• Bent at room temperature and Ic measured at 77K


Closing remarks

• SuperPower 2G HTS conductor offers a flexible architecture to address the broad range of demanding applications requirements

• SuperPower is engaging major resources in improving its manufacturing capabilities to deliver a consistent, reliable, high quality 2G HTS product– Improved mechanical properties– Improved piece length / uniformity– Improved current density– Improved splice resistance

• Alternative conductor configurations are being developed to address customer specific requirements– Ag alloy– Bonded conductors

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2G HTS Properties Beyond Critical Current

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