AC losses in prototype multistrand conductors for warm dielectric cable designs

We report on multiphase ac losses in four-layer prototype multi-strand conductors (PMC's) wound from HTS tape provided by American Superconductor Corporation. These conductors are prototype warm (near room temperature) dielectric cable designs, such as for the US Dept. of Energy's Superconductivity Partnership Initiative Project at Detroit Edison. We report on single phase "two phase" (no current in the PMC but with an external ac magnetic field generated by the two normal conductors arranged at the remaining corners of an equilateral triangle forming a three-phase configuration), and balanced three phase losses. Losses were also measured using a set of saddle coils to apply an ac magnetic field to the PMC. The losses were measured as a function of temperature, frequency, and current. We compare the losses for three PMC's, one (4LA) wound conventionally with equal pitch angles for all layers and the two others (4LB and 4LC) wound to achieve equal current distribution (UCD) among the layers, and thus lower single-phase losses in the operating region. In addition, 4LC was wound with a newer generation tape having a higher critical current. The PMC 4LC was found to have the lowest single, two-phase, and three-phase losses.