Loss and Transition Studies of Shunted Free-Stabilized YBCO Tape for SFCL Applications

Superconducting fault current limiters (SFCL) use the transition of superconducting materials as the mechanism to introduce high impedance in the line to be protected when the current in the line surpasses the fixed maximum value. When the normal working current passes through the line, the device exhibits almost zero impedance. The transition of the superconductor may be due to the current crossing the material or the magnetic field surrounding the material. In order to evaluate the possibilities of externally shunted non-stabilized YBCO tape for the design of resistive SFCL with transition by current and magnetic field, a study of this tape was made. First, the AC loss was determined as a function of the rms value of the transport current. This permits us to know what cooling power is required in the normal state and the value of the critical current that makes the material transit. Second, we studied the tape stabilized by external resistances, to get information about the behavior of the tape carrying current greater than the critical current. Finally, the variation of the critical current and AC loss in the presence of magnetic fields was studied. Some comments about the relation between all these parameters and the possibility of designing SFCL using this tape are included as conclusions.