  Minimization of ac losses is essential for economic operation of
high-temperature superconductor (HTS) ac power cables. A favorable
configuration for the phase conductor of such cables has two counter-wound
layers of HTS tape-shaped wires lying next to each other and helically wound
around a flexible cylindrical former. However, if magnetic materials such as
magnetic substrates of the tapes lie between the two layers, or if the winding
pitch angles are not opposite and essentially equal in magnitude to each other,
current distributes unequally between the two layers. Then, if at some point in
the ac cycle the current of either of the two layers exceeds its critical
current, a large ac loss arises from the transfer of flux between the two
layers. A detailed review of the formalism, its application to the case of
paramagnetic substrates including the calculation of this flux transfer loss is
presented.
