This paper proposes a methodology through an optimization model that allows decisions about expansion of a power system considering intermittent renewable energy sources, like wind energy, and other random variables in transmission and generation expansion planning. So, the uncertainty of the risk of failure in the system components, uncertainty in demand and uncertainty in the availability of energy resources (wind speed for wind power generation) is included. The methodology is applicable to systems with a high level of hydroelectric sources. It is divided in two parts, the first one establishes the best location of intermittent sources, like wind energy. The second part optimizes the combination between renewable sources and conventional generation. After that, the transmission facilities are formulated and optimized.