Mechanical Properties of Roebel Coated Conductor Cable A.Kario 1, S. Otten 1,2, C. M. Bayer 1, M....
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Transcript of Mechanical Properties of Roebel Coated Conductor Cable A.Kario 1, S. Otten 1,2, C. M. Bayer 1, M....
Mechanical Properties of Roebel Coated
Conductor Cable
A. Kario1, S. Otten1,2, C. M. Bayer1, M. Vojenciak1,3, A. Kling1, B. Ringsdorf1, B. Runtsch1, W. Goldacker1
1 Karlsruhe Institute of Technology, Institute for Technical Physics
2 University of Twente, Chair of Energy, Materials and Systems
3 Institute of Electrical Engineering, Slovak Academy of Science
Motivation
• Bending properties
• Tensile stress
• Transverse stress
• Need of impregnation
current
fieldforces
G. Kirby et al., EuCARDII Meeting
Bending radii > 10 mm do not degrade the Ic
• Cable geometry: 12 mm cable, 10 strands, TL: 126 mm
• Measurements on single strands show degradation in
the bent section by < 1%
• Small degradation, < 6.5 % of total cable Ic
• Cable degradation was not caused by bendingr = 50 mm
r = 10 mm
10 20 30 40 50500
600
700
800
900
1000
REBCO - outside
REBCO - inside
Ic (A)
radius (mm)
10
12
14
16
18
20n-value
To be published
Roebel cable is fragile to bending-torsion
0 10 20 30 40 50 60 700.5
0.6
0.7
0.8
0.9
1.0
15 mm, sc outside
Winding angle [°]
Ic norm [A]
10 mm, sc outside
10 mm, sc inside
15 mm, sc inside
10 %
5 %
LN2, SF
0 10 20 30 40 50 60 700.0
0.2
0.4
0.6
0.8
1.0
15 mm, sc outside
Winding angle [°]
Ic norm [A]
10 mm, sc outside
10 mm, sc inside
LN2, SF
• No reversibility in a case of 10 and 15 mm
thickness
• 5% or 10% degradation at 20° winding angle
Cable
10 or 15 mm diameter
Modelling of the stress in meander structure
• 4 mm Roebel cable
• Superpower tape: 100 µm thick, Yong modulus: 120 GPa
• Applied tensile load 1 kN
• Finite Element Method, Comsol Multiphysics
C. Barth et al., Supercond. Sci. Technol. 25 (2012) 025007 (9pp)
Roebel strand geometry: outer corner and 10 mminner radius
• High von Mises stress – concentrated in small areas, favour the growth of cracks
• Low von Mises stress – distributed over large area, cable can withstand high tensile load
C. Barth et al., Supercond. Sci. Technol. 25 (2012) 025007 (9pp)
• degradation of the
individual strands Ic
by 30% at a transverse
stress of 10 MPa.• KIT cable: 10 strands, TL: 126 mm
• Effective stress: 167 MPa (24% surface)
• GCS cable: 15 strands, TL: 300 mm
• Effective stress: 111 MPa (36% surface)
Different compressive stress values 10 – 40 MPa
J. Fleiter et al., Supercond. Sci. Technol. 26 (2013) 065014 (5pp)
D. Uglietti et al., Supercond. Sci. Technol. 26 (2013) 074002 (5pp)
Transversal stress test with additional copper strands
• Contact area of stainless steel: 4 mm x 85 mm
stainless steel
Roebel strands
Copper strands
0 10 20 30 40 500.5
0.6
0.7
0.8
0.9
1.0
Ic normalised n-value
pressure (MPa)
5 % Ic degradation =
27.7 MPa
2
4
6
8
10
12
5% Ic degradation by 68.8 MPa effective stress
• Average transverse stress (cable surface)
• Effective transverse stress
0 20 40 60 80 100 1200.5
0.6
0.7
0.8
0.9
1.0
Ic normalised
pressure (MPa)
n-value
5 % Ic degradation =
68.8 MPa
2
4
6
8
10
12
To be published
Defects on the Roebel-bridge
1 2 3 4 5 60
10
20
30
40
50
60
70
straightstraightbridge bridge
strand 3 strand 4 strand 5 strand 6 strand 7 strand 8 strand 9
Ic (A)
position on Roebel strand
bridgestraight
60 K, 20 mT
61 K, 30 mT
2 mm
2 mm
60 K, 25 mT
2 mm
Magneto-optical Imaging
• Ic measurements after deassembly of the
Roebel cable To be published
Epoxy choice
• Commercially available resins with
fillers
• Thermal expansion
• Thermal conductivity
• Chemical compatibility with REBCO
• Resin working temperature
• Resin viscosity
Stress concentrations
Low Tc cable example
Fred M. Asner, High Field Superconducting Magnets, CLARENDON PRESS OXFORD 1999
Thermal expansion similar to REBCO for more then 50% filled epoxy's
• Thermal expansion < 0.7 % preferred
* C. Barth,PhD thesis (2013)
Unfilled epoxy
Carbon p. + C
NT (4-8 %
)
Graphite + C
NT (4-8 %
)
Al(OH)3 (5
6 %)
Silver (6
0-80 %)
Silica (5
0 %)
Silica (6
0 %)
Graphite (5
0-60 %)
Alumina (60-70 %
)
REBCO tape
-1.60
-1.40
-1.20
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
N. Bagrets, ITEP, KIT
*
*
*
Thermal expansion (%)
*
To be published
Equal thermal conductivity at 4.2 K for silica and alumina filled epoxy's
• At 4.2 K, all epoxies have very low thermal conductivity
• Effect of fillers is small compared to 77-300 K
* C. Barth, PhD thesis (2013)
Unfilled epoxy
Carbon p. +
CNT (4-8 %
)
Graphite
+ CNT (4-8 %
)
Al(OH)3 (5
6 %)
Silve
r (60-80 %
)
Silica
(50 %
)
Silica
(60 %
)
Graphite
(50-60 %
)
Alumina (60-70 %
)
REBCO tape
0
0.2
0.4
0.6
0.8
1
1.2
1.4
S. Drotziger, ITEP, KIT
*
**
λ (W/ m*K) λ (W/ m*K)
300 K
Unfille
d ep
oxy
Carbo
n p.
+ C
NT (4-8
%)
Graph
ite +
CNT (4
-8 %
)
Al(OH)3
(56
%)
Silver
(60-
80 %
)
Silica
(50
%)
Silica
(60
%)
Graph
ite (5
0-60
%)
Alumina
(60-
70 %
)0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
4.2 K
*
* *
To be published
Impregnation of dummy Roebel cables
• Wet-winding
• Vacuum impregnation with fused silica
• Vacuum impregnation with fused silica and glass fibre
To be published
Vacuum impregnation with Araldite and 50% fused silica
• Dummy between two stainless steel tapes
• Araldite CY5538/HY5571 with 50 wt% fused
silica
• T = 80 °C, P = 0.3 kPa
• Thickness < 1 mm → high current density
100 µm stainless steel tape
Epoxy filledcentral hole
Ic [A] n
Before impregnation 171.7 28.1
After impregnation 170.2 26.8After impregnation 2x 170.9 28.5
• Dummy with one SP REBCO strand
• Ic measurement at 77 K
• No Ic degradation
To be published
Transverse pressure tests (U. Twente)
W. Van de Camp, master thesis, University of Twente, 2012
Samples to be tested
• Reference cable
• Impregnated cable
(CY5538/HY5571 + 50 wt% silica)
Cryogenic press (UTwente)
• T = 4.2 K
• Imax = 50 kA
• Bmax = 11 T (perpendicular)
• Fmax = 260 kN
• U-shaped samples
Bending
• Easy direction down to 10 mm radius: TL:126 mm, 10 strands cable
• Depends on: TL, no. of tapes, SC tape
Tensile stress
• Optimised structure: outer corner,
inner radius 10 mm (fixed)
Transverse stress
• Impregnation support needed
Impregnation
• Vacuum impregnation with Araldite 50% fused silica proposed
Summary
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Bending properties
ImpregnationTransversal
stress
Tensilestress