A transmission tower (colloquially termed an electricity pylon in the United Kingdom and parts of Europe, an ironman in Australia, and a hydro tower in parts of Canada) is a tall structure, usually a steel lattice tower, used to support an overhead power line. They are used in high-voltage AC and DC systems, and come in a wide variety of shapes and sizes. Typical height ranges from 15 to 55 metres (49 to 180 ft), although heights in excess of 300 metres (980 ft) exist. In addition to steel, other materials may be used, including concrete and wood.
Four major functions of transmission towers are in use suspension towers, terminal towers, tension towers, and transposition towers. Some transmission towers combine these basic functions. Transmission towers and their overhead power lines are often considered to be a form of visual pollution. Methods to reduce the visual impact include undergrounding.
(Wikipedia, Jan 2012)