Verification of a design technique of an SFCL system with a copper bypass reactor

This paper presents a study on design technique of superconducting fault current limiters (SFCLs) with a bypass reactor. The SFCL system consists of a non-inductive superconducting coil and a copper coil as a bypass reactor. Since typical resistive SFCL impedance is too high to adopt the existing grid protection scheme, a bypass reactor is required to adjust the impedance. The superconducting coil is a current-driven passive element; hence, connecting a bypass reactor in parallel affects the current sharing between the superconducting coil and the copper reactor. We proposed a design technique to estimate the generated impedance considering the current sharing. The technique is based on a SPICE simulation and thermal finite element analysis (FEA). By comparing to the test result with two kinds of bypass reactors, it is confirmed that the proposed method can simulate all currents and voltages properly. As a result, a case study was conducted on the design of the SFCL system, rated on 13.2 kV/2.5 kA was being considered as a new distribution grid in Korean metropolitan areas.