Conductors made of high-temperature (HTS) wires helically wound in one or
more layers on round tubes (CORT) are compact, flexible, and can carry a large
amount of current. Although these conductors were initially developed for DC
applications, e.g. in magnets, it is worth considering their use for AC, e.g.
in underground cables for medium voltage grids and with currents in the
kA-range. In these cases, the major challenge is reducing AC losses. In
contrast to a straight superconducting wire, in a helical arrangement, due to
superconducting shielding, the current does not follow the direction of the
wires, but takes a non-trivial zig-zag path within the individual HTS wires
(Garber pattern). This includes current components across the thickness of the
superconducting layers, so that the often used thin-shell approximation does
not hold. In this contribution, we studied a one-layer three-wire CORT by means
of fully three-dimensional simulations, based on the H-formulation of Maxwell's
equations implemented in the commercial software package COMSOL Multiphysics.
As a result of our simulations, the peculiar current profiles were confirmed.
In addition, the influence of current, pitch angle, and frequency on the AC
losses was studied. We found an optimum for the pitch angle and that the
current profiles strongly depend on frequency