This paper present solution of optimal power flow problem using a firefly algorithm (FA) with consideration of FACTS devices "UPFC". The objective is to minimize the total fuel cost of generation and also maintain an acceptable system performance in terms of limits on generator real power and reactive power outputs, bus voltages and power flow of transmission lines. In order to maximize the relief of congestion in power system, to reduce the total system real power loss and improves the

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... ity of the system we propose also the optimization of the placement of FACTS devices in the power system (UPFC). The proposed method is tested on IEEE 30-bus system and the Algerian electrical network. The result of this method is compared with those obtained by biogeography based optimization (BBO), genetic algorithm (GA), and artificial bee colony (ABC) algorithm.