Analysis on Protection Coordination Between Overcurrent and Undervoltage Relays According to Current-Limiting Reactor/Resistor of SFCL in Power Distribution System

In a power distribution system supplying 6.6 kV to multiple feeders connected to various loads, a fault on one feeder can result in voltage drops across other connected feeders. Voltage sags can severely affect on facilities with rotating machinery by causing motors to draw excessive current to maintain output power and continuous or repeated voltage sag lead to overheating, insulation damage and motor failure. This paper studied protection coordination between under voltage relay (UVR) in a sound feeder and overcurrent relay (OCR) in a faulted feeder considering application of a superconducting fault current limiter (SFCL). Proper current limiting reactor/resistor (CLR)’s value comprising the SFCL to ensure the coordination between OCR and UVR was investigated to prevent relay malfunction. Through the comparative analysis due to the impedance magnitude of resistive and inductive CLRs, the proper CLR value of the SFCL was confirmed to be required to protect sensitive rotating machinery load.