Study on Protection Coordination of a Flux-Lock-Type Superconducting Fault Current Limiter Using Switches

Power systems have been continuously expanded to complex networks, due to the growth of power demand and additional installation of substation facilities, and the countermeasure to protect these power systems from the increased fault current is required. Among the various methods, the superconducting fault current limiter (SFCL) has been noticed as the more effective protective device. The flux-lock-type SFCL, which is composed of two coils wound on the iron core and superconducting (SC) element, is known to be effective for reducing the burden of SC element, by adjusting either the inductance ratio or the winding direction between two coils. However, for the higher impedance of the SFCL, the higher resistance generation in the SC element comprising the flux-lock-type SFCL during the fault period is needed, which makes the power burden of the SC element more increased. Additionally, the long recovery time of the SFCL into the normal state after the fault removes affects the operation of the protective relay such as the overcurrent relay. In this paper, as the countermeasure for the protection coordination between the flux-lock-type SFCL and the overcurrent relay, the flux-lock-type SFCL using the switches was proposed. The proposed flux-lock-type SFCL using the switches, which can bypass the fault current through the operation of the switches into its current-limiting resistance (CLR) with the same amplitude as the SC resistance comprising the flux-lock-type SFCL, is expected to be operated to limit the fault current without the delayed recovery time. Through the case studies using computer simulation, the protection coordination of the proposed flux-lock-type SFCL using switches was validated.