Conductor systems for overhead lines: some considerations in their selection

The selection of conductors for a modern overhead transmission or distribution system is an exercise in optimisation and balancing of conflicting requirements. Service experience and environmental considerations may often challenge established concepts for the design of future lines. The reasons for the predominance of aluminium-based conductors are outlined, and the wide available range of such conductors and the properties of each main variant are described. The influence of manufacturing processes in conductor design is set out, and the important role played by greasing is emphasised. These considerations are shown to lead to the selection of particular conductors in each of the voltage bands from 1.v. to u.h.v. Factors discussed include load density and growth, climatic environment, strength, standardisation, corrosion, external loading, corona effects and economics. The paper proceeds to describe the effects of aeolian vibration, subconductor oscillation and galloping on the choice of conductor and fittings, and on conductor bundle geometry. The rather different emphasis in choosing conductors for distribution systems is also discussed and the overriding need for standardisation stressed. The need for conductor-material specifications and acceptance testing is recognised, and the paper concludes with a brief outline of possible future trends in conductor engineering.