Experimental Investigation and Modelling for the Optimisation of Conduction Cooled THS Hybrid Current Leasds for SMES

It‘s importat that HTS tapes have lower thermal conductivity and higher transversal resistivity in order to reduce the heat leaks conducted along the tapes and AC losses in the high temperature superconducting system conduction-cooled by GM coolers,This paper presents an experimental investigation into the effects of pure Ag and AgAu alloys sheath materials on the properties of Bi(2223) multifilamentary tapes and the optimisation of conduction-cooled hybrid current leads made from copper and Bi(2223)/Ag or Bi(2223/)AgAu tapes,The thermal conductivity of the tapes were measured by cryogenic steady healt flux method and the resistance was measured by using standard DC four-probe method at lo temperature,The results showed that the reduction of thermal conductivity by the addition of Au into the sheath material of Bi(2223) tapes was 65%,75% and 85% lower than that of pure Ag sheathed Bi(2223) tapes and the increase of resistivity was 4.9,10 and 19.4 times higher than that of pure Ag for the addition of 2.2%,5.7% and 10.7% Au(atom ratio )respectively.And the study also attempts to optimise thermodynamically the conduction-cooled hybrid current lead by using a devel-oped model ,which took the irrevesibility of commercial GM coolers,the contact resistance and thermal conductance into account,Predictions from the model showed that AgAu alloys were suitable candiate materials to replace Ag as sheath material of Bi(2223) tapes applied in THS current leads,In addition,Bi(2223)/AgAu was a suitable material to be applied as the THS section of hybrid current leads in conduction-coled superconducting electric systems.