Coordination of directional overcurrent relays using a novel method to select their settings

This study presents a new method to select the settings of directional overcurrent relays. First, a new selection criterion of pickup currents is adopted. It results in discrete pickup current values, which mitigate the selectivity constraints effect on the minimisation of time multiplier settings. Second, the selectivity constraint equations are classified into individual groups with respect to backup relays. When solving these systems of equations, the initial time multiplier settings are obtained. The initial values are then increased gradually to find the final solution for all of the constraint equations. The proposed method is tested for three networks: 8-bus system, IEEE 14-bus system and IEEE 30-bus system. Its performance is evaluated and compared with the linear and non-linear programming techniques.