Fault current limiting characteristics of resistive type SFCL using a transformer

A transformer is expected to be an useful component of resistive type superconducting fault current limiter (SFCL) using high-T-C superconducting (HTSC) element with constant critical current for easier adjustment of both the limiting impedance and the initial limiting current level. Therefore, the analysis for the fault current limiting characteristics of the resistive type SFCL using a transformer considering the resistance variance of HTSC element is needed because the resistance of HTSC element during a fault period is affected by the design condition of the transformer. In this paper, we investigated the limiting impedance and the initial limiting current level of the resistive type SFCL using a transformer as a function of the turn numbers' ratio between the primary winding and the secondary winding. The limiting impedance of SFCL was extracted by applying discrete Fourier transform (DFT) equation for the measured voltage and current data of SFCL. It was confirmed from the analysis that the transformer design with the lower turn numbers' ratio of the primary winding for the secondary winding was advantageous for the larger load current capacity of SFCL and that the transformer with the higher ratio design condition, on the other hand, was favorable for the larger fault current limiting capacity of SFCL.