Mitigation of DGs Impact on Variable-Topology Meshed Network Protection System by Optimal Fault Current Limiters Considering Overcurrent Relay Coordination

Abstract

- In this paper, the optimal deployment of fault current limiters (FCLs) in a variable-topology distribution network with distributed generators (DGs) is analyzed. FCLs are used to mitigate the negative impacts of DGs on overcurrent protection system of the distribution network including escalated electromagnetic stresses, costly replacement of some protective devices, and protection miscoordination. A proposed multi-objective optimization scheme is applied to maximize the mitigation effect of FCLs and minimize their total cost. The scheme determines the optimal locations of the FCLs and the associated optimal impedance values. Meanwhile, a particular focus is kept on preserving the coordinated operation of the protective directional overcurrent relays (DOCRs) of the distribution network under any operating conditions. DOCRs coordination preservation is merged into the FCLs allocation problem by a compulsory set of main-backup DOCRs pairs operation constraints for both near-end and far-end faults at every possible network topology. Furthermore, to lessen the cost of FCLs, a new hybrid approach is developed. Firstly, optimal re-adjusting of a selected small percentage of the DOCRs is done for just one time at nearly zero cost. Then, the FCLs allocation problem is solved. Different engineering strategies for maintaining DOCRs coordination are compared for a 33 kV meshed case-study system.