Application of genetic algorithm to overcurrent relay grading coordination

To guard against the possible failure of main protection devices in power system protection, the overcurrent (OC) relay is usually employed as backup protection to prevent the system from suffering catastrophic consequences. OC protection devices and their variants represent the largest installed base of protective equipment on any distribution system and may be considered as the backbone of any protection strategy. Their individual operation is a standalone tripping action made without other relay information except the current transformer (CT) input only. This paper describes the grading coordination of OC relays with normal IDMTL (inverse definite minimum time lag) characteristic complying with the IEC 255-4 standards