AC losses in a superconductor for the quick response type 70 MW class superconducting generator

The authors have been developing a 70 MW class model superconducting generator aiming at a 200 MW class pilot machine. The superconductor developed for the field winding of the generator has a configuration of double stranded cable, consisting of NbTi, Cu, and CuNi. Then, for the purpose of decreasing intra-strand AC losses, a strand with additional Cu-0.5 wt%Mn fins in the Cu sheath has been developed. The authors have carried out tests and analytical studies of the generator AC losses. They then compared cables with additional fins in the Cu sheath with cables without fins. The results show that both eddy current losses and coupling losses in the strands were considerably reduced by additional fins in the Cu sheath.