In this article a model and a solution methodology is presented to solve the transmission network expansion problem, considering the selection of the wire size and the construction technology of the conductors for transmission lines for each new right-of-way. The optimization problem is solved using a specialized genetic algorithm that uses the logic of the Chu-Beasley Genetic Algorithm combined with an exact technique. The methodology is tested in the Colombian electric system of 93 buses and 155 candidate lines, which is modified in order to allow investment options for the selection of the conductors. The results obtained improve the traditional solution for the Colombian electrical system in the transmission planning study.