Effect of transverse load on the critical current of a coated conductor Roebel cable
Roebel cables are one possible option for use in the manufacture of high current conductors for various technical applications. In this work the behaviour of critical current under transverse loads up to 90 MPa was studied in coated conductor Roebel cables. First the critical current evolution under transverse load was measured on 4 mm wide coated conductor tapes with Hastelloy substrate (copper surround stabilizer) and on punched tapes, which are used for the assembling of Roebel cables. It was found that they were able to withstand large transverse loads (> 100 MPa) with less than 2% degradation of the critical current at 77 K. In contrast, with tapes, a significant reduction of the critical current (> 20%) was observed in Roebel cable samples at pressure as low as 10 MPa. Marks of mechanical defects were observed in the strands extracted from the cable. Measurements of the local critical current on extracted strands confirmed that in the regions which were visually damaged the critical current was also reduced. The defects are attributed to pinching (stress concentration), which takes place in the cable. The results suggest that the integration of coated conductor Roebel cables into large systems should be carefully evaluated.