Development of a Niobium-copper-invar composite conductor for an AC superconducting power transmission cable

A superconducting ac power cable has been developed using Nb/Cu/Invar composite conductors and shields in a coaxial configuration with pressurized. He at 4.7 K as the primary dielectric. Two major concerns for this cable system were the accommodation of fault currents and the differential thermal expansion between the conductor assembly and the cryogenic envelope. We have shown that a Nb/Cu/Invar composite tube is capable of accommodating the fault currents as well as the differential thermal expansion. Studies of the effect of surface finish on the ac losses showed that with proper surface finish, the losses can be reduced to an acceptable level for power cable applications. The lowest 60 Hz losses measured at a peak surface magnetic field of 0.1 T correspond to 43 watts per 3-phase mile for a 138 kV, 3400 MVA power cable.