Requirements of conductors for overhead lines

A conductor for an overhead line should carry current efficiently and safely for many years under mechanical and weather loads. Its main requirements are:

1. High electrical conductivity (low resistivity) to reduce $I^2R$ loss and voltage drop.
2. High tensile strength to withstand its own weight, wind and ice loading and allow long spans with less sag.
3. Low specific gravity (light weight) so that towers can be lighter and sag is smaller.
4. Low cost and easy availability so the line is economical.
5. Flexibility: easy to handle, string and wind on drums (achieved by stranding).
6. Durability and corrosion resistance against weather and pollution.
7. Low coefficient of thermal expansion so that sag does not change much with temperature.
8. High melting point / ability to work hot to carry overloads and short-circuit currents.
9. Larger diameter (for EHV) to reduce corona.
10. Not brittle; should resist fatigue from vibration.

ACSR meets most of these requirements and is widely used in Nepal's transmission and distribution lines.