LINEAR-PROGRAMMING FOR DIRECTIONAL OVERCURRENT RELAY COORDINATION IN INTERCONNECTED POWER-SYSTEMS WITH CONSTRAINT RELAXATION

A linear programming method with constraint relaxation is applied to the directional overcurrent relay coordination problem in an interconnected power network. This method allows for hierarchical constraint relaxation and removal in cases where an infeasible problem exists. This method is applied to coordinate the directional overcurrent relays for an example interconnected power network with six buses and seven lines. Different suggestions for choosing the pickup current and the resulting time dial settings are presented. These results are compared with those given by the break-point approach. A complete algorithm for calculating the time dial settings corresponding to given pickup currents is introduced to make this method suitable for computer implementation.