Multiphase ac loss mechanisms in HTS prototype multistrand conductors

We report on multiphase ac losses in four-layer prototype multi-strand cond uctors (PMCs) wound from high temperature superconductor (HTS) tape provide d by American Superconductor Corporation. "Two-phase" losses are induced wi th no current flowing in the PMC but with all sc magnetic field generated b y currents flowing in the two normal conductors arranged at the remaining c orners of an equilateral triangle forming a three-phase configuration, This is a typical configuration that a pow er cable of the "warm dielectric" de sign could have, The losses were measured at 65 to 76 It, in a frequency ra nge from 10 to 180 Hz, and for currents from 600 to 1600 Arms. We compare t he losses for two PMCs, one wound conventionally with equal pitch angles fo r all levers and the second wound to achieve uniform current distribution ( UCD) among the layers. The UCD method results in I educed single-phase loss es at currents greater than about 1/2 of the critical current. However, the two-phase losses are somewhat larger for the PMC wound by the UCD method. We investigated this difference empirically and theoretically.