Recent progress in superconducting transmission

Expected requirements for high-capacity, modest-cost underground transmission of energy have motivated intense development of superconducting power transmission lines. Recent studies and laboratory developments have generated much reason for optimism. The U.S. now has three ongoing projects to develop superconducting cables - a rigid ac system design employing Nb conductors, a flexible ac system employing Nb3Sn tapes, and a flexible dc cable system design employing Nb3Sn tape or multifilamentary conductors. In addition there are a number of supporting research projects in the fields of cryogenic dielectrics, helium fluid flow and heat transfer, cryogenic refrigeration, and superconducting materials. This review paper presents an overview of these ongoing activities.