Cryopower transmission studies in Europe

European studies on cryopower transmission are focused on semiflexible and totally flexible superconducting cables. Intense investigations of cable components are being performed. Nb/Cu and Nb/Al composite conductors have been developed, which exhibit 50 Hz surfaces losses well below the design limit of ac cables at 4–6 K and surface peak flux densities up to 0.1 T. Measurements of breakdown voltages and dissipation factors at 4 K indicate that wrapped tape electrical insulation, impregnated with helium, may be suitable for superconducting cables, the achievable dielectrical strength being about 10 kV mm^?1 (rms). But further investigations are necessary within this topic. Different types of dc and ac cable joint and terminal have been designed or already constructed. A number of larger laboratory model tests with cable sections up to 50 m length have been performed or are planned for the near future with the aim of studying size effects, the interaction of different components and to demonstrate the feasibility and performance of superconducting cables.