Stability of fault current limiter with conduction cooled Bi2223 screen

摘要

We examined a stability of magnetic shield type fault current limiter (MSFCL) with Bi2223 screen cooled by cryocooler thermally. Conduction cooled MSFCL handles better and needs easier maintenance than that cooled by liquid cryogen. In addition, the cost of the MSFCL decreases by the decrease of the required volume of the superconductor with the increase of the critical current density. We made the small model of the MSFCL with Bi2223 ring, ac loss of one ring under a normal operating condition was measured at 30 K determined by the critical current density of Bi2223 short sample. The measured ac loss almost corresponded to the hysteresis loss calculated from Beam model. The ac loss of the MSFCL with the shielding body of the stacked Bi2223 rings for 6.6 kV-1 kA distribution power system was calculated from Bean model. From the relation between the required number of the rings and the critical current density, the design outlines of the shielding body of conduction cooled MSFCL was obtained. The MQE of one Bi2223 ring of the small model was measured, and we confirmed that the MSFCL using high T_c superconductor had high stability against a local heat disturbance even at 30 K. In the case of the MSFCL with the stacked rings for a distribution power system, the improvement of the stability due to the current sharing between rings was confirmed by the numerical calculation.