Fault-Current Limiting Properties in Innovative Force-Free Superconducting DC Cable

We proposed the innovative force-free superconducting cable with higher current-carrying capacity than conventional superconducting DC cables utilizing the longitudinal magnetic field effect that enhances the critical current density. That is, the critical current density can be enhanced by the longitudinal magnetic field that the conductor itself and the outer shield conductor produce. It means that, if the longitudinal magnetic field can be reduced, the critical current density is appreciably reduced, resulting in an accelerated resistive transition. Such situation can be realized by arranging the copper conductor layers in a suitable structure that transport currents when the superconductors are in resistive state. We propose to arrange the copper conductor layers in the inner and outer conductors to reduce the longitudinal magnetic field by twisting in opposite directions to respective superconducting layers in each conductor region. Various conditions of fault-current limiting can be achieved by arranging the winding angle of the copper layers. Discussion will be given on the fault-current limiting properties of the proposed cable.