What are typical examples for the application fields of both metals?

For overhead lines, the weight of the cables is the deciding factor, so mostly aluminium is used. That means thicker conductors, but that does not make such a big difference for the design of an overhead line.

For high-voltage underground cables, on the contrary, copper is more suitable. The highest material cost of such cable is its insulation. Aluminium would mean a thicker conductor, so more insulation material to surround it, which would result in a more expensive cable. Consequently, in this case, the lower volume of copper is often preferred.

Another advantage of copper for underground applications is its high resistance against corrosion. For the same reason, bare overhead lines in coastal areas are sometimes made of copper instead of aluminium.