This page was last edited on 25 June 2017, at 20:26. They are used in high-voltage AC and DC systems, and come in a wide variety of shapes and flexible ac transmission system pdf download. In addition to steel, other materials may be used, including concrete and wood.
Some transmission towers combine these basic functions. Transmission tower” is the name for the structure used in the industry in the United States, and some other English-speaking countries. The term “pylon” comes from the basic shape of the structure, an obelisk-like structure which tapers toward the top, and the name is mostly used in the United Kingdom and parts of Europe in everyday colloquial speech. If a line is constructed using towers designed to carry several circuits, it is not necessary to install all the circuits at the time of construction. Some high voltage circuits are often erected on the same tower as 110 kV lines.
Paralleling circuits of 380 kV, 220 kV and 110 kV-lines on the same towers is common. With bipolar systems, a conductor arrangement with one conductor on each side of the tower is used. In this case, it had to be installed with insulators equipped with surge arrestors on the pylons in order to prevent electrochemical corrosion of the pylons. For single-pole HVDC transmission with ground return, towers with only one conductor can be used. In many cases, however, the towers are designed for later conversion to a two-pole system. In these cases, often conductors on both sides of the tower are installed for mechanical reasons. Until the second pole is needed, it is either used as electrode line or joined in parallel with the pole in use.
Electrode line towers are used in some HVDC schemes to carry the power line from the converter station to the grounding electrode. 30 kV, but normally carry only one or two conductors. Steel tube or concrete poles are also often used for these lines. As a rule, the towers of railway traction lines carry two electric circuits, so they have four conductors. These are usually arranged on one level, whereby each circuit occupies one half of the cross arm. For four traction circuits, the arrangement of the conductors is in two-levels and for six electric circuits, the arrangement of the conductors is in three levels.
Pylon in Sweden about 1918. Unsourced material may be challenged and removed. AC circuits of different frequency and phase-count, or AC and DC circuits, may be installed on the same tower. Usually all circuits of such lines have voltages of 50 kV and more.