Study on selection of SFCL´s impedance for protection coordination with overcurrent relay in a distribution system

The continuous increase of power demand has resulted in an excess of the rated capacity of the distributed power transformer and the replacement with the larger power transformer is under consideration. However, the larger power transformer has lower impedance, which increases the short-circuit current and exceeds the cut-off-ratings of the circuit breaker in a distribution system. The superconducting fault current limiter (SFCL) has been noticed as the promising method to decrease the short-circuit current in a power system, because it has no power loss in a normal time and can limit the fault current rapidly without additional device to detect the fault current. These merits of the SFCL have made many researchers to adopt the SFCL as one of better solutions to decrease the short-circuit current effectively due to the replacement of the larger power transformer with its lower impedance. However, the protection coordination of the protection devices such as the over-current relay (OCR) and the recloser in a distribution system gets out of the original setting rule due to the introduction of the SFCL. In this paper, we studied on the impedance of the SFCL for the protection coordination with the protection devices in a distribution system. Through the analysis using PSCAD/EMTDC, it was obtained that the range of the impedance of SFCL would be drawn to keep the protection coordination.