S. M. Mousavi Agah - Member, IEEE
H Askarian Abyaneh - Member, IEEE

Relay coordination of distribution networks is somehow similar to the transmission networks bysome differences. The most important one is the nature of distribution feeders are usually cables. When afault occurs, fault current should be cleared by main overcurrent relays. If the main relays fail to operate,backup relays should clear the fault current after discrimination time. Occurrence of high current faultswith delayed operation time of backup relays, may cause thermal damages to the cable insulations indistribution networks. Optimum coordination of overcurrent relays for both distribution and transmissionnetworks have been developed by many authors before. The authors of this paper have developed a newmethod for overcurrent relay coordination using Genetic Algorithm (GA). In this paper the ObjectiveFunction (OF) of the existing GA method is improved to consider the cable thermal damage curves. Theadvantages of this method are decreasing the ageing rate of the cable insulations and increasing reliability ofthe distribution networks. The algorithm is applied to a sample distribution network and results shows thenew settings are more realistic than the results of the previous methods.

Distribution Networks, Power System Protection, Overcurrent Relays Coordination, Power Cable Insulation, Insulation Ageing, Damage Curve