Instability in kiloamp class a.c. superconducting cables

In kiloamp (kA) class superconducting cables for a.c. use, where each strand does not have an insulation layer, the quench current in 60 Hz operation was found to be no more than 50% of the d.c. critical current, even on the load line. The degradation in the 60 Hz quench current of the kA class cables is discussed with respect to: 1, an a.c. instability in the multifilamentary wire; 2, magnetic coupling among strands in concentric multistrand cables; 3, the influence of local disorder in cabling on current distribution; and 4, the temperature rise due to steady a.c. losses. While points 2 and 3 induce non-uniform current distribution, points 1 and 4 were found to be factors in the reduction of quench current in the strands with higher current density. Some local overheatings may also contribute to the intense degradation.