The Amazon region is characterized by its exuberant jungle, by the abundance of its hydroelectric resources, so far not well exploited and by the low amount and big sparsity of electric energy consumption in its vast territory. In such region, around 50% of available Brazilian hydroelectric resources are situated at a distance of roughly 2000 km far from the big consumption centres, most of which at South-eastern and Southern areas. The transmission of large blocks of power requires therefore the development of overhead lines having high power-carrying capabilities; besides, for developing such systems, huge financial amounts are necessary, so that the transmission systems need to be economically enough designed so as to provide the electric energy to the consumers at a competitive cost. During the last three decades, Eletronorte, the Brazilian state-owned Utility responsible for generation and transmission in Northern Brazil, has studied and implemented several overhead lines aimed at improving the cost/benefit ratio of its electric system, this meaning systems able to carry higher amount of electric energy at the lowest possible cost. Inside this context, the present report describes the evolution of overhead line conception, especially their steel supports, as well as the basic line designs for 230 kV and 500 kV levels, developed in the last years by Eletronorte and engineering companies for carrying higher and higher powers per circuit. At first, it will be shown how the Utility has faced and overcome the challenge of developing 230 and 500 kV overhead lines providing high Surge Impedance Levels, as required for transmitting large power blocks to distant regions. The evolution of the mechanical design of the towers will be presented, considering the options of compact towers and/or bundle expansion, starting with the self-supporting “racket” tower, continuing with cross armless towers, either of the Chaînette type or cross-rope version, ending with a new tower type recently under evaluation and introduced. Therefore, it will be shown that this new conception is gaining technical and economical attractiveness, namely single-mast guyed towers provided with expanded-bundle configurations. Concluding, the compaction techniques associated with the expanded-bundle conception using the last mentioned single-mast guyed structures have made possible to implement overhead lines with a transmission capacity 20% higher and cost 25 % lower than the corresponding figures obtained with the conventional designs, being such new “optimized” conceptions available to transmission system planners and transmission line designers, opening therefore new possibilities for the optimization of electric systems.