Overhead lines: equipment. - Conductors and ground wires

This article specifies the characteristics of bare cables for overhead line construction: conductors and ground wires.

In recent decades, there has been no significant change in the choice of conductive metals. Almost exclusively :

• high-purity, cold-worked aluminum in bimetallic aluminum-steel cables;

• an aluminum alloy, almelec, which has a significantly higher mechanical tensile strength than aluminum, making it possible to produce homogeneous cables consisting solely of almelec wires.

Recently, however, with the aim of increasing the transmission capacity of certain existing lines without significantly altering the environment, conductive metals that can withstand higher operating temperatures than aluminum or almelec have been studied. The conductors installed in various countries appear to have acceptable behavior, enabling the structures to be strengthened.

Another avenue of research is currently the subject of experimentation: this consists in producing conductors made from assemblies of conductive materials and composites (carbon fibers), so as to obtain high-performance cables that are not very sensitive to temperature variations. To date, this research has not led to any satisfactory experiments.

In recent years, cables with built-in communication circuits have been increasingly used. Fiber-optic cables are now being laid throughout the entire transmission network, to enable the installation of high-speed digital data transmission if required. This is in line with the decisions taken by the Comité Interministériel pour l'Aménagement du Territoire (Interministerial Committee for Regional Planning) on July 9, 2001, aimed at serving the whole of France with equivalent and satisfactory performance.

In distribution networks, the proportion of underground pipes has increased in extension and renewal projects, while that of bare cables has fallen significantly.

For low-voltage lines, pre-assembled conductors are systematically used: these are not dealt with in this article.