Limiting Impedance of Flat Type Fault Current Limiter with High Tc Superconducting Plate

We have proposed a flat type of the superconducting fault current limiter (FCL) which is a modified version of a magnetic shielding type of the fault current limiter. The new FCL basically consists of a spiral coil and a doughnut-like form high Tc superconductor (HTS) plate, each of which works as a primary winding and a secondary one-turn winding, respectively. The FCL modules can be easily built up to make a large scale FCL. This simple construction may enable us to reduce the manufacturing costs. Small modules of the flat type FCL were made with Bi2223 bulk plate and the normal and limiting impedance due to a normal load current and fault excess current were measured. It was confirmed from experiments and magnetic field analyses that the ratio of the limiting impedance to the normal one was improved by using the iron core. Although the relatively low impedance ratio was derived in our experiments, a magnetic field analysis sugested that the high impedance ratio in order of 103 might be realized by completely covering the spiral coil and HTS plate with the high permiability material such as an iron.