Abstract
A Nb3Sn composite conductor with about 10 thousands submicron diameter filaments has been manufactured by the external diffusion process. Fine filament size of 0.53μm (design value), a tight twist pitch of 0.87mm for the wire diameter of 0.153mm and bronze matrix resulted in a strongly reduced a.c. losses: the hysteresis loss and the coupling current loss were observed to be 465kW/m3 and 96kW/m3 respectively in the a.c. field of 50Hz with an amplitude of 2.0T. A triplex conductor was constructed by cabling three strands at a twisting pitch of 3mm and a small coil (inner diameter 11mm, outer diameter 33mm, axial length 19mm) was wound from this cable. In the d.c. mode operation, the coil generates a field of 1.3T at the critical current of IC=37.4A. When the coil is operated at 50Hz with an exciting current of IC, the observed loss averaged over the windings was 240kW/m3. The quenching current in 50Hz operation was 53A at the maximum field of 1.8T, which is considerably higher than the critical value under d.c. condition. Preliminary studies have shown that, if this conductor is used in superconducting armature windings of rotating machines, economical benefits are obtained compared with conventional armatures.
