Coordination of overcurrent relays in distribution system using linear programming technique

A power system consists of many number of equipment. Much more number of circuit breakers and relays are required to protect the system. The relays in the power system are to be coordinated properly so as to avoid mal-operation and hence to avoid the unnecessary outage of healthy part of the system. The overcurrent relays are the major protection devices in a distribution system. Overcurrent relay is usually employed as backup protection. But in some situations it may be the only protection provided. A relay must get sufficient chance to protect the zone under its primary protection. Only if the primary protection does not clear the fault, the back-up protection should initiate tripping, and therefore, overcurrent relay coordination in power distribution network is a major concern of protection engineer. The overcurrent relay 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 interruption of the power supply and to avoid the mal-operation of relays. This paper discusses linear programming technique for optimum coordination of overcurrent relays in a ring fed distribution system.