  Unlike low temperature superconducting cables, there is so far no perfect
solution for REBCO coated conductors to form a fully transposed high current
cable. Every REBCO cable concept must import a stack of tapes to achieve an
operating current as high as tens of kiloamperes. The stacked REBCO tapes, no
matter whether they are twisted or not, however, have a nature of
non-transposing and therefore could result in current unbalance. In this
manuscript, the current unbalance and the related electrical characteristics of
a cable made of 40 stacked REBCO tapes are studied with an electrical circuit
simulation. The differences in splice resistances and tape inductances that are
both related to the non-transposed structure of a REBCO stack are considered.
Results show that for a 40 cm long termination, a proper method to keep the
contact resistivity between each tape and the copper termination around 1e-8
ohmm is crucial to totally avoid current unbalance lowering the cable
performance. Surprisingly, the inter-tape current transfer is found to be able
to further exacerbate local high current though it does make the overall
distribution more balanced. The inductance difference induced current unbalance
is only important if local defects exist at long REBCO tapes, which on the
other hand can be cured by good inter-tape current transfer. For a
fast-charging rate of 1 kA/s, the inter-tape contact resistivity should also be
low to a level of 1e-8 ohmm to ensure a short current transfer length of around
1 m.
