초전도 한류기의 과도상태시 전력망 동작특성

Abstract

The superconducting fault current limiter (SFCL) is a fault current limiter that uses the characteristic of the superconductor, which operates without loss under the normal state but quickly generates impedance to limit the fault current under the transient state after a fault occurrence. To apply the SFCL to the distribution or transmission system, the capacity problem should first be addressed. Studies are being conducted to improve the capacity of the SFCL using a transformer. This study examined the operation and application characteristics of the flux-coupling type SFCL with an integrated three-phase transformer under the transient state of the power system. The integrated three-phase flux-coupling type SFCL limits the fault current dividing into faulted and sound phases in the system. According to this characteristic, in the case of a single, double or triple line-to-ground fault, all superconducting elements in the faulted and sound phases were quenched, and approximately 60% or more of the fault current was limited. In the case of a double or triple line-to-ground fault, however, the fluxes from faulted phases were crossed, and the limiting rate of fault current was decreased from that of the single line-to-ground fault. To apply the SFCL to the power system, the capacity improvement, coordination with the protection system and SFCL application positions should be considered. In this study, the coordination with the reclosing duty cycle of the power system was examined by analyzing the recovery characteristic of the superconducting element depending on the application of simultaneous quench when the capacity of the integrated three-phase flux-coupling type SFCL was increased. In addition, the fault current patterns were analyzed according to the SFCL application positions in a distribution system. The analysis results showed that the decrease in the rated current induced to the sound feeder was improved when the SFCL was installed on the feeder. When the SFCL was installed on the secondary side of the main transformer, the system protection range became wider, but the rated current in the feeder further decreased, making the stable power supply impossible.