Preliminary Design and Test of Low-Resistance High Temperature Superconducting Short-Circuited Coils

Despite their relatively high volume and weight, inductive fault current limiters with high temperature superconducting (HTS) secondaries have already proven their viability, especially the transformer topology. Volume and weight make them inappropriate for transmission grids, but they can e.g. promote the advent of renewable energy sources in medium voltage electric distribution networks while maintaining short-circuit current levels consistent with existing protections ratings. These devices make use of a short-circuited HTS secondary, which typically requires non-superconducting joints. Although jointless HTS secondaries have already been built (by means of e.g. opening slits in the tapes) these have no application in real scale devices. In this paper, a new engineering design of low-resistance HTS short-circuited coils, intending applications in distribution grid fault current limiters, is proposed. This design allows building coils with an arbitrary number of turns and a single joint only, thus providing an effective way of adjusting the parameters of limiters (e.g. activating current). A prototype coil is built, and the manufacturing process is described. The proposed concept is experimentally validated by measurements of contact resistance and induced superconducting currents.