Transient thermal characteristics of cryocooler-cooled HTS coil for SMES

Thermal behavior of high-temperature super-conducting (HTS) coil is exceedingly different from that of low-temperature superconducting (LTS) coil. Therefore for the sake of the application of HTS coil to practical use, establishment of a new stability criterion for coil design becomes indispensable. In this study, a small-sized cryocooler-cooled HTS coil wound with Bi-2223/Ag tape was constructed and tested to evaluate the electromagnetic and thermal characteristics in the cryocooler-cooled HTS coil. We carried out experiments subjected to pulse current operation supposing SMES for power system stabilization. The simulation by a newly developed computer program based on the finite element method (FEM) agreed well with experimental results. In the computer program, short-sample data concerning the E-J characteristics, which depend on the orientation of applied magnetic field to the wide face of Bi-2223Ag tape, was adopted. By using the computer program, we also evaluate the thermal behavior of HTS coil graded according to the magnetic field distribution.