Optimal Application of Fault Current Limiters for Assuring Overcurrent Relays Coordination with Distributed Generations

Abstract

This paper addresses the problem of overcurrent relays (OCRs) coordination in presence of DGs. OCRs are optimally set to work in a coordinated manner to isolate faults with minimal impacts on customers. Penetration of DGs into the power system changes the fault current levels seen by the OCRs. This can deteriorate the coordinated operation of OCRs. Operation time difference between backup and main relays can be below the standard limit or even the backup OCR can incorrectly work before the main OCR. Though resetting of OCRs is tedious especially in large systems, it cannot alone restore the original coordinated operation in the presence of DGs. The paper investigates the optimal utilization of fault current limiters (FCLs) to maintain the directional OCR-coordinated operation without any need to OCRs resetting irrespective of DGs status. It is required to maintain the OCRs coordination at minimum cost of prospective FCLs. Hence, the FCL location and sizing problem are formulated as a constrained multi-objective optimization problem. Multi-objective particle swarm optimization is adopted for solving the optimization problem to determine the optimal locations and sizes of FCLs. The proposed algorithm is applied to meshed and radial power systems at different DGs arrangements using different types of FCLs. Moreover, the OCR coordination problem is studied when the system includes both directional and non-directional OCRs. Comparative analysis of results is provided.