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