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Splice Resistance

 

Voltage-current (VI) relationship is one of the most important aspects of the performance of a coated conductor. Using the four-probe transport measurement, a 2G wire splice fabricated in our lab was normally characterized with its joint section located in between the two voltage taps. The data provided here were mainly obtained from the measurements carried out at 77 K with a splice sample immerged into liquid nitrogen and with no applied magnetic field.  Depending on the sample dimension, our lab is also capable of characterize splice joints at lower temperatures and in magnetic fields up to 6 Tesla.

 

 A typical VI curve obtained from a splice joint is shown in the Figure 1 below. For this measurement, the voltage tap spacing is 8.9 cm. In the VI plot, the unit for the voltage is millivolt and the unit for the current is ampere. It can be seen from the plot that the voltage increases linearly with the increase of the current in the regime where the current is below the critical current (Ic). This is due to the resistance from the splice joint. That is different from the VI relationship of a bare coated conductor wire where the voltage signal is basically the instrument noise in this regime. The splice resistance is then simply defined as the slope of the linear part of the curve. For this sample, the resistance of the splice is about 200 nW. A VI curve can also be plotted in the log-log scale as shown in Figure 2. For each of the splice, the VI curve is provided in both linear and log-log scale.

 

Figure 1. The VI curve of a splice plotted in linear scale.

 

 

Figure 2. The VI curve of a splice plotted in log-log scale.

 

Table 1 & Table 2 below list the resistance values of splices fabricated with various 2G wires. Soldering process was carried out by either a soldering iron or a soldering heater block. Soldering materials recommended by the wire manufacturers were used for making these splices. All the soldering materials including solders and fluxes are commercial products. Soldering temperature is determined according to the melting point of the solder used and is the maximum temperature allowed for the processing of the specific 2G wire. As soldering temperature is an important processing parameter, it is also listed for each splice fabricated and measured. Unless specified otherwise, all splices were made as in the lap joint geometry with an overlap length of ~ 2.5 cm. In most cases, the tapes are in the orientation such that the HTS side of one tape facing the HTS side of the other tape (denoted as HTS-HTS). This is schematically shown in Figure 3. In other cases, the tapes in a joint can be in the orientation such that the HTS side of one tape facing the substrate side of the other tape (denoted as HTS-SUB). Splices between 2G wires and normal copper conductors were also fabricated for testing, where the joint orientation is denoted as either HTS-Cu or SUB-Cu. For given resistance value, it is the result of a group of 6 samples that were made with the same wire and using the same soldering conditions. By clicking on any resistance value listed in Table 1 & Table 2 you can view the VI curves of the splice, which is a typical one of the 6 samples in the group.

Figure 3. Lap joint geometry of a splice with the tapes in HTS-HTS orientation.

 

Table 1 Electrical resistance values of the splices fabricated using the AMSC’s HTS 2G wires

Sample ##

2G Wire

Orientation

Solder

Flux

Soldering T (°C)

Resistance

A01

344C

HTS-HTS

52In48Sn

Alpha 260HF

150

32±9.8nW

A02

344C

HTS-HTS

100In

Alpha 260HF

165

26±5.5nW

A03

344C

HTS-HTS

67Bi33In

Alpha 260HF

150

0.62±0.57mW

A04

344B

HTS-HTS

52In48Sn

Alpha 260HF

150

180±20nW

A05

344B

HTS-HTS

52In48Sn

Kester 135

150

180±20nW

A06

344B

HTS-HTS

100In

Alpha 260HF

165

200±60nW

A07

344B

HTS-HTS

100In

Kester 135

165

180±20nW

A08

344B

HTS-HTS

67Bi33In

Alpha 260HF

140

0.63±0.50mW

A09

344B

HTS-Cu

52In48Sn

Alpha 260HF

150

26.7±0.52mW

A10

344B

SUB-Cu

52In48Sn

Alpha 260HF

150

34.2±1.5mW

A11

344B

HTS-Cu

100In

Alpha 260HF

165

27.6±1.6mW

A12

344B

SUB-Cu

100In

Alpha 260HF

165

34.1±1.6mW

A13

344B

HTS-HTS

50In48Sn

Alpha 260HF

160

75±5.5nW*

A14

344B

HTS-HTS

50In48Sn

Alpha 260HF

160

55±5.5nW**

A15

344S

HTS-HTS

52In48Sn

Alpha 260HF

165

5.77±1.5mW

A16

344S

HTS-HTS

100In

Alpha 260HF

170

6.15±1.9mW

                                                                      *Overlap length is 5 cm.

                                                                      **Overlap length is 7.5 cm.

 

 

Table 2 Electrical resistance values of the splices fabricated using the SuperPower’s HTS 2G wires

Sample ##

2G Wire

Orientation

Solder

Flux

Soldering T (°C)

Resistance

S01

SCS4050

HTS-HTS

60Sn40Pb

Kester SP-44

195

20±2nW

S02

SCS4050

HTS-HTS

100In

Kester SP-44

195

20±2nW

S03

SCS4050

HTS-Cu

60Sn40Pb

Kester SP-44

205

27.4±0.58mW

S04

SCS4050

HTS-Cu

100In

Kester SP-44

195

26.5±0.44mW

 

 

 

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