Electricity Today T&D Magazine

Three-phase electric power systems are used for high and extra-high voltage AC transmission lines (50kV and above). The pylons must therefore be designed to carry three (or multiples of three) conductors. The towers are usually steel lattices or trusses (wooden structures are used in Germany in exceptional cases) and the insulators are generally glass discs assembled in strings whose length is dependent on the line voltage and environmental conditions. One or two earth conductors (alternative term: ground conductors) for lightning protection are often added to the top of each pylon.
Detail of the insulators (the vertical string of discs) and conductor vibration dampers (the weights attached directly to the cables) on a 275,000 volt suspension pylon near Thornbury, South Gloucestershire, England. In some countries, pylons for high and extra-high voltage are usually designed to carry two or more electric circuits. For double circuit lines in Germany, the “Danube” towers or...