Optimization of BSCCO/Ag-tapes for high current and for AC-applications

摘要

For improving the application possibilities of (Bi,Pb)_2Sr_2Ca_2Cu_3O_x/Ag-tapes in cables or transformers it is necessary to increase the overall critical current density and to develop tapes with low AC-losses. For enhancing the overall critical current density j_e, the filling factor of the tapes was increased from 28% to 38%, and the thermo-mechanical treatment (TMT) process was optimised. Due to the large number of parameters of the TMT process (at least temperature, oxygen partial pressure and dwell time of three different treatment steps, if the temperature ramps, and the parameters of the intermediate rolling procedures are kept constant) the application of the method of design of experiments can be very useful. The number of experiments can be reduced and the method gives additional information about the process, especially the statistical significance of the process parameters and about interactions between different parameters. As a result of these investigations j_e could be enhanced to 10 kA cm~(-2) (I_c = 90 A). Twisted tapes have been developed in order to reduce the AC-losses. The influence of twist pitch on the critical current density and the AC-losses has been studied. In twisted tapes with a twist pitch of 10 mm AC-losses as low as 0.45 mW A~(-1) m~(-1) (0.1 T||, 50 Hz) and overall current densities up to j_e=4.5 kAcm~(-2) were measured.