II. OPTIMAL RELAY COORDINATION PROBLEMS
Overcurrent relays are devices which have ability to interrupt electricity supply service due to some severe fault. In a modern electrical power system, network interconnection is very complicated. This affects the difficulty of key parameter setting of protective relaying devices [5]. When a total number of overcurrent relays to be coordinated is increased or even feeding in closed-loop configuration is required according to a complex transmission network, overcurrent relay coordination setting is more difficult.