New approach to coordination of distance relay zone-2 with overcurrent protection using linear programming methods

The paper presents a new method for the coordination of distance zone-2 and overcurrent relays by using linear programming methods. For this purpose, a topological analysis is first carried out to identify the set of primary and back-up relays. The coordination constraints are then used in the linear programming methods, where, for zone-2, operating time is set independently for each distance relay and the results are compared with the case where all the zone-2 time settings are the same. Three linear programming methods are studied for solving the problem. The methods are tested for a typical interconnected network and the results are presented and compared.