A transmission tower is a tall structure

Structure

Structure is a fundamental, tangible or intangible notion referring to the recognition, observation, nature, and permanence of patterns and relationships of entities. This notion may itself be an object, such as a built structure, or an attribute, such as the structure of society...

, usually a steel lattice tower

Lattice tower

A lattice tower or truss tower is a freestanding framework tower. They can be used as electricity pylons especially for voltages above 100 kilovolts, as a radio tower or as an observation tower....

, used to support an overhead power line

Overhead power line

An overhead power line is an electric power transmission line suspended by towers or utility poles. Since most of the insulation is provided by air, overhead power lines are generally the lowest-cost method of transmission for large quantities of electric energy...

. 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 m (49.2 to 180.4 ), although heights in excess of 300 metres (984.3 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

Dead-end tower

A dead-end tower uses horizontal strain insulators and occur at the endpoints of conductors. Such endpoints are necessary when interfacing with other modes of power transmission and, due to the inflexibility of the conductors, when significantly altering the direction of the tower line...

, and transposition towers.