Actual interconnected power systems are very large structures which suffer from a large gap between electricity demand and generation and from an inadequate transmission capacity of interconnection lines. In such systems, blackouts have become an all too common an occurrence. This paper proposes a method to reinforce the power systems by insertion of FACTS (flexible alternating current transmission system) devices, which are optimal placed in order to eliminate the dangerous contingencies of the systems and to prevent by this way the apparition of blackout if outages occurs. The FACTS devices are optimal placed in order to maximizing the power system security, the optimization is carried out using three parameters: the location of FACTS devices, their type and their sizes. For this purpose we developed a hybrid software based on GAs (genetic algorithms), which uses Matlabtrade and the EUROSTAGtrade software for load flow calculations. The proposed procedures are successfully tested on an IEEE 14-bus power system