Abstract: The first step in the planning of the electrical supply networks consists in defining the optimum placement of one or more power stations; this can be done by the centre of gravity method, or by the minimal reduced costs. The first method take in account only the optimisation of investments, tended that the second in addition to the investments holds operating statement "production cost, cooling and transport." In this study, we show also the strategy and the criteria of delimitation of the zones to electrify by the same departure and to reduce the transfer of power between zones, which has as a consequence a better plan of voltage.