Stability, Inter-Strand Contact Resistance and AC Losses in YBCO Roebel Cables
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Citation:Published version: IEEE Transactions on Applied Superconductivity (Volume: 24, Issue: 3, June 2014) Article Sequence Number: 6600505. https://doi.org/10.1109/TASC.2013.2283472
A dc transport current was applied to the strands of a Roebel cable at 77 K in liquid nitrogen bath. The inter-strand contact resistance was measured. It was modified either by applying a pressure on the cable at 77 K in liquid nitrogen bath or using different soldering patterns between the strands of the cable. Magnetization ac losses were measured in frequency range 50 – 200 Hz in applied magnetic field 4 – 70 mT perpendicular to the broader face of the cable to test the inter-strand contact resistance effect. High stability and very low level of coupling losses was observed in the cables even with the lowest interstrand resistances.
In an effort of aiming current sharing between the strands in Roebel cables we studied experimentally the effect of different kinds of inter-strand connections on inter-strand resistances. Just applying a pressure of 8 kPa gives a maximum interstrand resistance of 105 mΩ. Using a tin foil placed on top of the Roebel cable gives the maximum inter-strand resistance of 31.5 mΩ under a pressure of 8 kPa. The lowest maximum inter-strand resistance of 0.1 mΩ was achieved by soldering copper shunts (strips 5 mm wide and 0.1 mm thick). Even such a low inter-strand resistance value does not cause any significant coupling loss increase up to 200 Hz. However, on the other hand it will allow some current sharing between the strands of the Roebel cables. Detailed experimental results on this subject will be published elsewhere.
This work was supported by the U.S. Department of Energy, grant DE-FG02-07ER84913.