Fundamental performance of flux-lock type fault current limiter with two air-core coils

This paper proposes a superconducting fault current limiter (FCL) which is a modified version of the flux-lock type fault current limiter developed by us. This FCL consists of a high T_c superconductor (HTS) and two coaxial air-core coils. One coil is connected in parallel with another one through the HTS. The HTS is arranged inside the coils. Under fault condition, the HTS generates resistance by a overcurrent. The limiting impedance appears in the FCL so that the overcurrent can be reduced. Furthermore, the resistance of the HTS increases because the HTS is exposed the magnetic field of the coils. As a result, we can obtain a larger limiting impedance in the current limiting phase. We concretely designed a 200 V class FCL with Bi2223 bulk and estimated the transient behavior in current limiting operation. It is confirmed that the magnitude of fault current was suppressed significantly by this type of FCL with Bi2223 bulk and that the limiting effect was slightly improved by the application of the magnetic field induced by two air-core coils.