PLACEMENT AND COORDINATION OF OVERCURRENT RELAYS IN POWER DISTRIBUTION SYSTEMS

Abstract

Directionally overcurrent relays are popularly used for the primary protection of distribution circuits. Directionally overcurrent relays are placed strategically through out the system and determination of settings of these relays is the core issue to properly coordinate them. In this dissertation work, the relay coordination problem is solved in non-linear environment after transforming it into a parameter optimization problem. The problem has been solved in non-linear environment by the Steepest Descent (Gradient) method with exterior penalty approach. A pre-processing algorithm is presented which helps in identifying infeasible and redundant constraints,, and thereby reducing the complexity of the problem. A new objective function is used, which significantly improves the selectivity and reliability of the protection system. By modifying the objective function to sum of minimization of constraint violations in place of the conventional objective function, it is expected that better settings for the relays will be obtained. A decomposition algorithm is presented to tackle the coordination problem of large power systems. New algorithms are developed for formulating the coordination problem and used for solving the coordination problems of a 6-bus and IEEE 14-bus test systems.