Adaptive optimum coordination of overcurrent relays for deregulated distribution system considering parallel feeders

Abstract

This paper proposes an adaptive optimum overcurrent protection for deregulated distribution networks containing parallel feeders. The proposed adaptive coordination eliminates the maloperation of conventional overcurrent protection under different fault scenarios. These scenarios take place when faults occur close to the end of the parallel feeders specially when faults are associated with significant fault resistances. Under these faults, the current at the backup relay is almost double that at the corresponding primary. Thus, adaptive pickup setting is recommended. However, this problem is complicated remarkably when distributed generation units feed the upstream source side faults or under the removal of the power source due to the interruption of a source side breaker. Simultaneously, the proposed coordination approach enhances the sensitivity and keeps on the optimum speed by automatically identifying the faulted zone. The faulted zone is identified by monitoring both the status concerning a single feeder or two parallel feeders in service and the faulted phase current direction of each pair of relays. Thus, a new fault direction identification method is presented. This method is based on comparing the angle of the post-fault current and that of the pre-fault current. Three optimization algorithms (genetic, harmony search, and water cycle algorithms) have competed to find the optimal settings of the installed overcurrent relays for each faulted zone. The reliability of the proposed method is examined as compared to conventional coordination concepts based on a detailed simulation of an actual 11-kV cascaded parallel series distribution feeder in the Egyptian distribution network. Sample results are examined.