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Conductor configuration and characteristics of superconducting cable for 50Hz a.c. use are reported. We developed a.c. conductors aiming low loss kA class current capacity. In consideration of reducing the current degradation by cabling, structures suitable for a.c. conductor are designed. In these conductors, low loss a.c. superconducting wires with very fine NbTi filaments are stranded around central cable of Cu-Ni or stainless steel wires for equal cooling condition, equal current distribution and mechanical reinforcing. Characteristics of small coils with these conductor at 50Hz a.c. load are tested and reported.

Stabilities of magnets in a high gravitational field up to 2000 G are discussed, based upon the experimental results of forced quench tests in a set of rotating magnets, in order to establish the stability design criterion of field windings of superconducting generators. Relations of propagation velocities, recovery currents, minimum quench energy and heat transfer characteristics are studied, a good agreement between the experimental results and a theory confirmed the improvement of magnet stability in a high gravitational field because of the enhanced heat transfer characteristics.