PSO-based Protection Coordination and Power-loss Minimization in Distribution Systems with DG Sources using Optimal Fault Current Limiters

Accommodation of DG sources in a radial distribution system may result in reversal of current flow in some feeder sections of the system with a subsequent protection mis-coordination. To maintain the protection coordination, DG sources are connected to the distribution system through fault current limiters (FCLs) whose impedances are unknowns. A method is proposed to formulate an optimization function to minimize power-loss and to ensure that the fault currents restore to their original values without DG sources. The proposed method is based on two approaches. In the two-stage approach, the sizes and locations of DG sources are determined in the first-stage followed by the determination of sizes of FCLs in the second-stage. In the single-stage approach, the sizes of FCLs as well as the sizes and locations of DG sources are determined simultaneously. Minimization of the objective function is achieved using Particle Swarm Optimization (PSO) technique to obtain the optimum impedance values of the FCLs in addition to the sizes and locations of DG sources. The method is applied to the Canadian benchmark 9-bus and the IEEE 33-/69-bus distribution systems. The obtained impedances of the FCLs as well as the sizes and locations of DG sources are correlated with those reported in the literature for the same distribution system.