This paper investigates the islands formation in initial stages of restoration process in blackout condition and studies the impacts of islands number variation on the process execution. In addition, a method is proposed to determining each island optimal boundaries. Then the effects of transmission lines Thyistor Controlled Series Compensators (TCSC) to facilitate restoration process and improvement of optimal solutions are studied. Energy Not supplied (ENS) index minimization is the objective function and the optimization method is Genetic Algorithm. The test network modeling has been done using a special appropriate chromosome coding. Various operational constraints such as voltage margins in buses, transmission lines capacities and generators loading limits have been considered in optimization process and final solution evaluation. The IEEE-118 bus network has been used as test system to assess the capabilities of the proposed method. Some obtained results have been given in the case study section.