Effect of Non-uniform Contact Resistance in Critical Current measurements of HTS Roebel Cables

High temperature superconductors can be manufactured in multi-strand configurations such as Roebel and CORC cables. There is very limited modelling examining the inhomogeneities in HTS Roebel cables. Thus a finite element model was developed to analyse the effects of non-uniform contact resistances and current redistribution, when attempting to define the critical current of the cable. Different defects were imposed on a single or pair of neighbouring strands to interrogate the modelled outputs. Types of defect included mimicking a poor contact caused during soldering to the current terminals or varying the inter-strand contact to account for twisting or orientating the cable. The model showed that if poor contact exists between neighbouring strands (tapes); this remains difficult to detect from the electric field data, however, if a poor contact exists at the current terminals, this can be identified, with the individual strand exhibiting voltages several orders lower than in all other strands. Introducing a single strand with low Ic characteristics only had a significant effect unless limited by at least 75%. The model will inform future experiments and can be used as a tool for to define the cable length and location of instrumentation to extract information about the critical current and locating the origins of current sharing.