Optimal Coordination of Directional Overcurrent Relays using Interval Two Phase Simplex Linear Programming

The coordination of directional over current relays in interconnected power networks is formulated as an optimization problem. When two protective apparatus installed in series have characteristics, which provide a specified operating sequence, they are said to be coordinated or selective. The coordination of directional overcurrent relays pose serious problems in the modern complex power system networks, which are interconnected. In this paper, the coordination of directional overcurrent relays is formulated using Linear programming two phase simplex method and intervals. The objective function to be minimized is defined as sum of the time dial settings of all the relays. The inequality constraints guarantee the coordination margin for each primary/backup relay pair having a fault very close to relay pair. Using this formulation the size of optimization problem is greatly reduced. The proposed method is implemented to a simple radial and IEEE 3-bus systems and proves its ability for optimal setting of relays without any miscoordination and in minimum operating time with bounded values.