The selection of the conductors for transmission lines, including their cross section and arrangement is a key point for a transmission line. This is specially true since the conductors represent between 30-35% of the total line cost or investment. The choice of the optimum conductor is a compromise between its mechanical and electrical properties, as well as the investment and the cost of the losses along the line.

Copper conductors were the first ones to be employed in overhead lines. They proved to be technically difficult to be used for long spans due to their high weight to strength ratio though. The cost of copper are also too high.

In 1900 aluminum was introduced. Aluminum have lower conductivity than copper (62%), but has significant lower cost than copper. However, they were also inappropriate for long span applications because of low strength.

ACSR or aluminum conductor steel reinforced, combined the relatively good electric properties of aluminum, with the high strength of steel. They are also have relatively reasonable cost.

Other conductors have been developed along the years such as:

AAC - Aluminum Alloy Conductor
ACS - Aluminum Clad Steel Conductor
ACCR - Aluminum Conductor Composite Reinforced

Aside from cost and strength, other points to consider in selecting a conductor are the following:

Corona Performance - It is a function of voltage level and depends also on the line and conductor configuration.

Impacts of Electrical Origin to the Environment - As much as possible, select a conductor which electrical characteristics has low impact on the environment. These impacts refer to the electrical and magnetic fields, radio interference, and audible noise.

After taking everything that is mentioned into account, an optimization can now be conducted, to seek the best technical and economic conductor.

Such studies takes into account the initial investments and also the cost of losses along the period of the line, reducing the cost to present values in order to have the same base to compare numbers for different alternatives.

It should be emphasized that other variables of subjective nature are sometimes also important such as standardization, difficulties of obtaining right-of-ways for new lines in the future, political reasons, among others.

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