Reduction of effect of coordination constraints in the linear optimization of operating times of overcurrent relays

We present a new algorithm of reduction of coordination constraints effect on relayspsila operating times by optimal choice of pickup currents using linear programming. Consequently, significant minimization of time multiplier settings was achieved. This algorithm was tested on the 8-bus system and IEEE 14-bus network. Its efficiency was investigated on a coordination problem solved in three different cases. In the first one, the linear programming technique was used but the effect of coordination constraints on operating times was not considered. In the second one, the nonlinear method was used to optimize the relay settings. In the third one, the effect of coordination constraints was reduced by application of the proposed algorithm, which resulted in substantial reduction in operating times as compared to the first method. In comparison to nonlinear methods, the new algorithm gives almost the same value of objective function. However, it does not require the rounding of pickup currents to their nearest available values.