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Considerations of weight factors and far-end faults in the directional overcurrent relay coordination problem formulation do not affect the optimal solution. This paper investigates this viewpoint and verifies that indeed by such an approach the optimality is not lost. But, this study reveals that in doing so, the coordination quality is sacrificed to some extent. It is also observed that if all remaining valid constraints (after relaxing few constraints based on the back-up coordination philosophy and strength of fault level generated) are considered and if the objective function is changed to running sum of all violating constraints, all valid considered constraints are satisfied. This study is done by simultaneously optimizing all settings in nonlinear environment by Sequential Quadratic Programming method using Matlab Toolbox. The results of the analysis on a sample 6-bus and IEEE 30-bus systems are presented in this paper.
Date of Publication: July 2006