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Electrical Tests of HTS Twisted-pair Cables With Helium Gas Cooling
Task 5. High Tc superconducting link
Partners
CERNR&D of HTS twisted pair cables
Bruker Energy & Supercon Technologies (BEST)R&D and Production of HTS Tapes
Columbus Superconductors R&D and Production of HTS Tapes
Institute of Cryogenics University of Southampton (SOTON)R&D of Cable operation and tests
Conductor Specs and Cables in Liquid Cryogens
Conductors ManufacturerConductor IC (A), 77K
Cable IC
(A), 77KCable IC (A), 4.2K
Type-1 Bi-2223 Bruker HTS 85 260 1220
Type-2 Bi-2223 Sumitomo 180 490 2880
Type-3 YBCO SuperPower 90 290 4410
Type-4 YBCO AMSC 90 300 3220
Type-5 MgB2 Columbus 330 @30K 4260
Test Setup at SOTON
helium bi-flow
in
out
out
helium uni-flow in
out
2m long cryostat with two inner vessels for He gas flow;
Independent flow control for each vessel
Copper/HTS current leads up to 3000 A
Multiple channel instrumentation for voltages and temperatures
Interlocks for quench protection
Cooling Configurations and Critical Current Measurements
UNI-FLOW: Positive temperature gradient along the cable in the flow direction; Analogue to typical cable/bus-bar applications; Ic onset always at the warm end;
BI-FLOW: Improved temperature uniformity along the cable; Suitable for assessing cable homogeneity and intrinsic properties
such as V-I;
helium bi-flow
in
out
out
helium uni-flow in
out
Critical Current Measurements
IC DETERMINATION: Whole cable IC undefined in the presence of a temperature gradient
for uni-flow. DC measurement of slow current ramp not suitable for gas cooled
long length cables as heat transfer may be insufficient to maintain a stable isothermal condition in the vicinity of IC;
A semi-transient protocol using square current pulses (1-10 s) was
adopted;
STABILITY NEAR IC:
An important requirement for the cable application;
Current Tests in Uni-flow: An Example of Type-3 Cable at 50 K
0.0
0.5
1.0
1.5
2.0
0
2
4
6
-8 -6 -4 -2 0 2 4 6
0.0
0.5
1.0
0
2
4
6
8
V14
, mV
800A-880A 800A-900A 800A-920A 800A-940A 800A-960A 800A-980A 800A-1000A 800A-1020A 800A-1040A 800A-1060A 800A-1080A 800A-1100A
V12
, mV
V23
, mV
V34
, mV
Time, s
0.0
0.5
1.0
1.5
2.0
-8 -6 -4 -2 0 2 4 60.0
0.5
1.00
2
4
6
0
2
4
6
8
V14
, mV
V12
, mV
Times, s
V34
, mV
V23
, mV
Uni-flow results in a temperature gradient along the cables, so that the warm terminal end is first to develop voltage; (Note the different V scales)
Voltage initially only appeared in a ¼ of the cable length (400mm);
Thermal runaway at currents ≥ 1060 A, faster at the resistive terminals;
Cables #1 and #2 exhibit similar behaviour indicating excellent reproducibility for cable production.
Overall
Warm terminal
Cable
Cold terminal
Cable #1 Cable #2 superimposed
V1 V2 V3 V4
T1 T1.5 T2 T3
0
1
2
3
V14
, mV
0.0
0.1
0.2
0.3
0.4
V12
, mV
0.0
0.5
1.0
1.5
2.0
V23
, mV
0 1 2 30.0
0.1
0.2
0.3
0.4
V34
, mV
Time, s
30K_840A 30K_855A 30K_870A 30K_870A-2 30K_885A 30K_900A 30K_915A 30K_930A 30K_945A 30K_960A 30K_975A 30K_990A 30K_1005A 30K_1020A 30K_1035A 30K_1050A
Current Tests in Bi-flow: An Example of Type-1 Cable at 30 K
With bi-flow, voltages are developed along the whole cable.
Although the two terminals had different contact resistances, their nonlinear resistance due to superconductors at higher currents are comparable.
Overall
Current lead terminal
Cable
Inter-cable terminal
V1 V2 V3 V4
T1 T1.5 T2 T3
V-I Characteristics can be obtained using the semi-transient method
0 1 2 3 410-5
10-4
10-3
10-2
V2
3
Time, s
100010-6
10-5
10-4
10-3
Vol
tage
s, V
Current, A
V23
32K 41K 57K 68K
V12
32K 41K 57K 68K
8(V12
-RC·I)
32K 41K 57K 68K
0.5 1 1.5 2 2.5 3
10-5
10-4
10-3
V23
, V
Current, kA
66K 57K
45K 28K
800 900 1000 110010-6
10-5
10-4
10-3
V12-V13 V11-V12 (V11-V12)-27nxI [(V11-V12)-27nxI]x8
Vol
tage
, V
Current, A
n=22
30K
Typical V (T) traces at different I pulses
Type#3 Type#1
Type#2
20 40 60 800.0
0.1
0.2
0.3
0.4
0.5
Con
tact
Res
ista
nce,
Temperature, K
Type#3 Type#1 Type#1 Type#1 Type#1 Type#2 Type#2 Type#2 Type#2
Contact resistances were also obtained for different temperatures. They are broadly consistent across different types, consistency can be improved.
Critical Current vs Temperature
0 20 40 60 800
1000
2000
3000
4000
5000
Crit
ical
Cur
rent
IC, A
Temperature, K
Type-5
Type-1
Type-3
Type-2
Filled symbols: pool coolingOpen symbols: gas cooling
Thermal stability near IC exists
0.0
0.2
0.4
0 1 2 3 4 5 6
0.0
0.2
0.4
10
20
30
40
2100A
Vol
tage
s, m
V
Time, min
850A
40
50
60
T3
T2
T1
V34
V23
Tem
pera
ture
, K
V12
0 2 4 6 80.0
0.1
0.2
0.3
0.4
0.5
Vol
tage
s, m
V
Time, min
26
28
30
32
34
T1,2,3
T4
V34
Tem
pera
ture
, K
V12
,V23
850 A
0.0
0.2
0.4
0.6
0.8
1.0
1860 A
1530A
990 A
660 A
0.0
0.2
0.4
0.6
0.8
0.0
0.2
0.4
0.6
0.8
Vol
tage
s V
12 ,
V23
, V
34 ,
mV
0 1 2 3 4 5 6 7 80.0
0.2
0.4
0.6
0.8
Time, min
26
28
30
32
34
36
38
40
42
44
54
56
58
60
62
Tem
pera
ture
T1
, T2
, T3
, T4
, K
64
66
68
70
72
V1 V2 V3 V4
T1 T1.5 T2 T3
Type#3
Type#1
Type#2
Conclusions
1. Tests on the twisted-pair cables carried out successfully on different types with He gas cooling.
2. Different cooling configurations were studied, uni-flow as in typical operation condition and bi-flow for near isothermal condition.
3. Homogeneity and reproducibility of cables confirmed with bi-flow. Consistency with results from measurements in liquid cryogens.
4. Thermal stability near IC were confirmed for all the types, including MgB2.
5. More work needed to understand the current sharing behaviour of MgB2.
6. Cables sufficiently robust for HTS links