Time Characteristic Curve Based Earth Fault Relay Selectivity Assessment for Optimal Overcurrent Relay Coordination in Distribution Networks

Coordination of overcurrent relays has been handled with optimization techniques. Time and pick up settings are optimized by using three-phase fault magnitudes. Generally, Standard Inverse Characteristic (SIC) has been used for three-phase fault protection settings. However, single line to earth fault is the most common fault types in distribution networks. Definite Time Characteristic (DTC) is, widely, used for coordination of earth fault relays. Topology type, neutral earthing resistance and capacitive currents of underground cables may cause selectivity issues when DTC is used for the coordination. In this work, time characteristic curve (TCC) based earth fault relay selectivity assessment carried out on distribution network. Different earthing resistance and TCC are taken into account during optimization processes. Results show that both DTC and SIC have issues in terms of operating time and selective protection.