Optimal co-ordination of overcurrent relays in the interconnected power systems using break points

• Finding the starting points for the optimal solution.
• Removing the conflict between constrains appearing in the interconnected networks by using breakpoints.
• Consideration of different type of OC relays with different curve types (both TMS and TDS curves are considered).
• Break point makes the optimal method applicable to on the real large interconnected networks (almost all of the paper in this field have been applied on the small test networks).

Interconnected power systems are multi-loop structured. In such networks, the determination of settings for all overcurrent relays can be carried out in different forms and may be quite complicated.Optimal coordination of overcurrent relays is a solution to find optimal time setting of the relays in interconnected networks. However, the optimal coordination method without using correct and efficient starting points i.e. the location of initial relays in the procedure for settings may cause many miscoordinations or the solution may not converge.In this paper an innovative approach is proposed in which both optimal coordination and break points for initial relays to find the settings of overcurrent relays are utilized. The fault location is in front of main relay and network configuration is so that maximum current flows through backup relay. Therefore, network configuration is taken into consideration and the suggested approach reflects configuration changes. A comparison between optimal coordination of overcurrent relays with or without break points and the conventional procedure of overcurrent relays coordination is presented.The results show the advantages of the proposed method.