The integration of high critical temperature (Tc) superconductors into the structure of current leads allows thermal and electrical losses to be reduced substantially. As a first step towards such hybrid leads for AC power applications in the kA range, DC demonstration current leads have been developed achieving 2 kA/20 kV. To this end, precursor powders and bulk parts together with their manufacturing processes have been developed and investigated for 4 different material options (ie sintered YBCO 123, melt textured YBCO 123, melt cast BSCCO 2212 and sintered BPSCCO 2223). The most suitable physical data and technical performance were found for the bismuth based compounds. Thus, a reduction of the 4 K heat load up to one tenth of conventional values was achieved in demonstration current leads operated at 1 to 2 kA. Lead operation with interface temperatures down to 67 K was shown to be feasible and realistic fault cases were mastered without any damage.
Thus, the partners succeeded in attaining the project goal, which was to verify the feasibility and economic advantages of applying HTSC to DC current leads in the kA range. In many aspects, the technological achievements represent worldwide top values.
Considerable potential for further development has become evident which applies especially to larger dimensions and higher currents and, very likely, to AC operation.
The improvements in the development of the high temperature superconductors especially with regard to the critical current densities in bulk material at 77 K, which have been obtained in the last three years, are encouraging to aim at short term applications in addition to the long term development of technical conductors.
The goal of the four companies during the course of this two years project is to develop current leads for 4.2 K-systems from high Tc superconducting materials, to manufacture them and to demonstrate the performances and the benefits in comparison with metallic current leads. They will be designed to real applications like current limiters and small and medium sized superconducting magnetic energy storage devices (SMES).
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