Overcurrent Relays Coordination in Interconnected Networks Using Accurate Analytical Method and Based on Determination of Fault Critical Point

Overcurrent relays should be coordinated for different operation conditions in interconnected networks. In addition, the time interval should not reach under the predefined threshold for each pair of primary and backup relays for the faults occurring in the protection zone of the primary relay. An analytical approach is presented in this paper to calculate the impedance matrix of the network in fault condition in order to determine the critical fault point accurately. Overcurrent relays are coordinated by using the presented critical fault point instead of the close-in fault used in previous studies. Simulation results show the accuracy of the proposed method for overcurrent relays coordination in comparison with other methods.