CTpr-rating Primary rating of CT Irelay Current seen by the relay OF Objective function TDSmin Minimum value for TDS TDSmax Maximum value for TDS

1841 M. Zellagui & A.Y. Abdelaziz, Optimal Coordination of Directional Overcurrent Relays using Hybrid PSO-DE Algorithm  Abstract — This paper presents a new approach for the optimal coordination of IDMT directional overcurrent relays in meshed power systems using a hybrid particle swarm optimization based differential evolution algorithm (PSO-DE). In protection coordination problem the total operating time of all main relays is minimized. Constraints of the problem are; backup relay should operate if primary relay fails to respond the fault near to it, Time Dial Setting (TDS) and Plug Setting (PS) and minimum operating time of relay. The operating time of IDMT directional overcurrent relays holds non-linear relationship with TDS and PS. The proposed hybrid optimization algorithm is to minimize total operation time for each protection relay. Two case studies are modeled and simulated to check the efficiency of the optimization algorithms such as IEEE 4-bus and IEEE 6-bus. The results are compared with the results obtained through other optimization algorithms. From the comparative results, it is found that the PSO-DE approach provides the most globally optimum solution at a faster convergence speed.