Analysis on Protection Coordination of OCRs Using Index for Impedance Compensation Considering Unsymmetrical Ground Fault in a Power Distribution System With SFCL

The superconducting fault current limiter (SFCL) has been spotlighted as the effective device to limit the fault current because it has no effect on a power distribution system in a normal time due to its zero resistance. However, the SFCL causes the trip of the overcurrent relays (OCRs) to be delayed due to the reduction of the fault current, which causes a negative impact on the protection coordination of power distribution system. The delayed trip of OCR makes the exposure time's increase of the neighboring power facilities from the fault current at fault line. In this paper, the OCR's index for the impedance compensation of the SFCL in case of the unsymmetrical ground fault was suggested. The suggested OCR's index consists of all sequence components for the impedance, calculated from the voltages and the currents measured from both the power distribution system and the SFCL. To prove the effectiveness of algorithm, the protection coordination between OCRs in a power distribution system with the SFCL were analyzed for the unsymmetrical ground fault as well as the symmetrical ground fault through the simulation using power system computer aided design (PSCAD)/electromagnetic transient design and control (EMTDC).