New Experimental Method for Investigating AC Losses in Concentric HTS Power Cables

The optimization of a high-temperature superconducting cable design with respect to ac losses is of crucial importance for the economic viability of the respective concept. However, the experimental determination of ac losses is not straightforward since, for short cable samples, the distribution of current among the superconducting tapes is mainly determined by the contact resistances of the individual tapes. The resulting inhomogeneous current distribution definitely falsifies the results. To solve this experimental problem, we present a new experimental technique. The setup is a 2-m-long three-phase concentric cable model for which, within each phase, the superconducting tapes (up to 30) are connected in series. The Cu-braid backwards conductors were assembled in a rotational symmetric cage-type arrangement, such that their self-fields at the cable cancel. If experimental peculiarities of this setup, as the strong inductive coupling between the phases and the suitable positioning of the voltage contact leads, are correctly taken into account, the currents can be controlled independently and the electrical properties of the cable can be measured unambiguously. In this paper, preliminary results are presented. The work is part of the German government-funded cable project AmpaCity (1 km/20 kV/2 kA).