Two approaches for directional overcurrent relays coordination in interconnected power systems with distributed generation

Abstract

Connection of distributed generation (DGs) powered by renewable energy resources in power systems has numerous benefits. However the presence of these (DGs) increase the fault current levels in different points, and disturb the protection coordination of the existing relays. Two approaches are proposed for coordination of directional overcurrent relays (DOCRs) in power systems with (DGs), depending on the types of system relays either adaptive or non adaptive. For adaptive protection system, the first proposed approach is based on linear programming technique which used to calculate the relay settings in case of DGs existing or not. For non-adaptive protection system, the second proposed approach is introduced, in which minimum impedance of fault current limiter is calculated to restore the coordination of relays without altering the original relay settings. The two proposed approaches are implemented and tested on IEEE-39 bus test system. Calculating load current in each relay by performing load flow analysis Yes No Calculating 3-ph, near-end fault primary and backup relays currents based on prefault condition without ZFCL increase ZECL Are all CTI j.,i > RCTI j.,i Calculating CTI for each relay pair Minimum ZFCL is obtained Modify the original case study network including DG Modify the original case study network including DG and ZFCL