Abyane - Khajeh Nasiraldin University
Ranjbar - Ministry of Energy
Golshan - Electric Power Research Center

To operate main and back up protective relays correctly, co-ordination between them is a vital job.In other word the settings of overcurrent (o/c), distance (DS) and combination of them should be co-ordinated. Combined overcurrent and distance relay settings procedure is completely different with overcurrent (O/C and DS) relays approach. Analyses of different ways of co-ordination of combination(between OC and DS) is made and optimum method for each case is chosen.According to these approaches which are completely new,a computer program has been developed. The program is tested on various power systems including Iran interconnected network. As an example some results of a real network are given in the paper.