Optimum Time Coordination of Overcurrent Relays in Distribution System Using Big-M (Penalty) Method

This paper presents big-M (penalty) method for optimum time coordination of overcurrent (OC) relays. The method is based on the simplex algorithm which is used to find optimum solution of linear programming problem (LPP). The method introduces artificial variables in the objective function to get an initial basic feasible solution (IBFS). Artificial variables are removed using iterative process which also leads to an optimum solution. The OC relays are the major protection devices in a distribution system. To reduce the power outages, maloperation of the backup relays should be avoided, and therefore, OC relay time coordination in power distribution network is a major concern of protection engineer. The OC relay time coordination in ring fed distribution networks is a highly constrained optimization problem. The purpose is to find an optimum relay setting to minimize the time of operation of relays and at the same time, to avoid the mal-operation of relays. Big-M simplex technique for optimum time coordination of OC relays in a ring fed distribution system is presented in this paper. Key-words: Backup protection, Big-M method, Constrained optimization, Overcurrent relay, Ring fed system, Time coordination.