Current Limiting Characteristics of a Flux-Lock Type SFCL Dependent on Fault Angles and Core Saturation

The flux-lock type superconducting fault current llmiter (SFCL) uses the magnetic coupling between two coils connected in parallel with each other. This SFCL has the merit that both the resistance of high-T_C superconducting (HTSC) element and the limiting current capacity can be simultaneously increased through the application of magnetic field into HTSC element. However, like other type of SFCLs using an iron core, unless the saturation of the iron core in the design is considered, the actual limited fault currents can be higher than expected as the saturation of the iron core occurs, and can lead to damage the electrical equipment of the power system. To analyse the dependence of the fault current in the flux-lock type SFCL on the fault angles, its electrical equivalent circuit with the magnetization branch was derived. From the electrical equivalent circuit, the fault current and the inner magnetic flux considering the fault angles as well as the design parameters such as winding direction and inductance ratio of two coils were calculated. The analysis results were compared with the experimental ones, and both the results agreed.