Analysis of joint-resistance-induced, non-uniform current distribution

The observation of nonuniform current distribution (NUCD) in multi-strand cables, in particular cable-in-conduit conductors (CICC's), has been reported often. NUCD may have important effects on AC loss and stability margin in such conductors; therefore, this phenomenon must be better understood. In this study, we have used numerical simulations to study the magnetic flux changes caused by NUCD's that themselves derive from details of lap-joint construction between cables composed of hundreds of strands and twisted in specific patterns. In the steady state, a NUCD is governed by the distribution and quantitation of contact resistances between individual strands in one cable to individual strands in the other. In an otherwise well-made joint, contact resistances will be lowest between strands that approach each other across the lap-joint-interface, and a strand that has many close encounters with the interface can be expected to carry larger current in the steady-state condition than a strand that has fewer or none. The length of the joint and the cable pattern determine the number of close encounters to the lap-joint-interface by individual strands. We present the results of our simulations using different joint length, we suggest experiments to observe these effects, and we discuss their significance with regard to conductor and magnet performance.