Abstract
The overhead line is the cheapest form of transmission and distribution of electrical energy. Line design and construction involve several engineering disciplines, such as electrical, civil, mechanical, and structural, and must conform to national and international specifications, regulations, and standards. These refer to conductor size and tension, minimum clearance to ground, stresses in supports and foundations, and insulation levels. Lines must operate in conditions of large temperature change and in still air and gales, and (in non-tropical climates) may have ice formation on conductors and supports. The structural design of a d.c. line does not differ essentially from that of an a.c. line, but electrical features related to frequency (such as inductive, capacitive, and skin effects) do not apply in the d.c. case under normal operating conditions. Many years of operating experience, and the costs as affected by metal market trends, have combined to favour aluminium based conductors.
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