Three-phase electric power systems are used for high and extra-high voltage AC transmission lines (50 kV and above). The towers must 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 either glass or porcelain discs or composite Insulators using Silicone Rubber or EPDM rubber material assembled in strings or long rod 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 mounted at the top of each tower.
In some countries, towers 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 more rarely, the "fir tree" towers, are usually used. 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. Sometimes, especially with 110 kV circuits, a parallel circuit carries traction lines for railway electrification.
High voltage direct current (HVDC) transmission lines are either monopolar or bipolar systems. With bipolar systems a conductor arrangement with one conductor on each side of the tower is used. 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, conductors are installed on both sides of the tower for mechanical reasons. Until the second pole is needed, it is either grounded, or joined in parallel with the pole in use. In the latter case the line from the converter station to the earthing (grounding) electrode is built as underground cable.
Towers used for single phase AC railway traction lines are similar in construction to those towers used for 110 kV-three phase lines. Steel tube or concrete poles are also often used for these lines. However, railway traction current systems are two-pole AC systems, so traction lines are designed for two conductors (or multiples of two, usually four, eight, or twelve). 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 crossarm. 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.
With limited space conditions, it is possible to arrange the conductors of one traction circuit in two levels. Running a traction power line parallel to a high voltage transmission lines for three-phase AC on a separate crossarm of the same tower is possible. If traction lines are led parallel to 380 kV-lines, the insulation must be designed for 220 kV, because in the event of a fault, dangerous overvoltages to the three-phase alternating current line can occur. Traction lines are usually equipped with one earth conductor. In Austria, on some traction circuits, two earth conductors are used.
Besides the obligatory high voltage warning sign, electricity towers also frequently possess a sign or circuit identification plate, with the names of the line (either the terminal points of the line or the internal designation of the EVU) and the tower number. This makes it easier identifying the location of a fault to the power company that owns the tower.
In some countries, electricity towers of lattice steel have to be equipped with a barbed wire barrier approximately 3 metres above ground in order to deter unauthorized climbing. Such barriers can often be found on towers close to roads or other areas with easy public access, even where there is not such a requirement.
To build branches, quite impressive constructions must occasionally be used. This also applies occasionally to twisting masts that divert three-level conductor cables.
Sometimes (in particular on steel framework pylons for the highest voltage levels) transmitting plants are installed. Usually these installations are for mobile phone services or the operating radio of the power supply firm, but occasionally also for other radio services, like directional radio. Thus transmitting antennas for low-power FM radio and television transmitters were already installed on pylons. On the carrying pylon of the Elbe Crossing 1 there is a radar facility belonging to the Hamburg water and navigation office.
For crossing broad valleys, a large distance between the conductor cables must be maintained to avoid short-circuits caused by conductor cables colliding during storms. Sometimes a separate pylon is used for each conductor. For crossing wide rivers and straits with flat coastlines very high pylons must be built, because a large height clearance is needed for navigation. Such masts must be equipped with flight safety lamps.
Two well-known crossings of wide rivers are the Elbe Crossing 1 and Elbe Crossing 2. The latter has the highest overhead line masts in Europe (height: 227 meters). The pylons of the overhead line crossing of the bay of Cádiz, Spain have a particularly interesting construction. They consist of 158-meter-high carrying pylons with one cross beam atop a frustum framework construction. The largest spans of overhead lines are the crossing of the Norwegian Sognefjord (span between two masts of 4,597 meters) and the Ameralik span in Greenland (span width: 5,376 meters). In Germany the overhead line of the EnBW AG crossing of the Eyachtal has the largest span in the country, a width of 1,444 meters.
In order to drop overhead lines into steep, deep valleys, inclined pylons are occasionally used. An example of this type of pylon is located at the Hoover dam in the USA. In Switzerland a NOK pylon inclined around 20 degrees to the vertical is located near Sargans. Highly sloping masts are used on two 380 kV pylons in Switzerland, the top 32 meters of one of them being bent by 18 degrees to the vertical.
Power station chimneys are sometimes equipped with crossbars for fixing conductors of the outgoing lines. Because of possible problems with corrosion by the flue gases, such constructions are very rare.
|Yangtze River Crossing||2003||China||Jiangyin||346.5m||Tallest pylons in the world|
|Yangtze River Crossing Nanjing||1992||China||Nanjing||257 m||Tallest pylons in the world, built of reinforced concrete|
|Pylons of Pearl River Crossing||1987||China||253 m + 240 m||830 ft + 787 ft|
|Orinoco River Crossing||?||Venezuela||Caroní||240 m||Tallest electricity pylons in South America|
|Pylons of Messina||1957||Italy||Messina||232 m (224 m without basement)||no longer used as pylons|
|Yangtze River Crossing Wuhu||2003||China||?||229 m||Tallest electricity pylons used for HVDC|
|Elbe Crossing 2||1976-1978||Germany||Stade||227 m||tallest electricity pylons in Europe|
|Chusi-Crossing||?||Japan||Chusi||226 m||Tallest electricity pylons in Japan|
|Overhead line crossing Suez Canal||1998||Egypt||221 m|
|Kerinchi Pylon||1999||Malaysia||Kerinchi near Kuala Lumpur||210 m||Tallest pylon in Southeast Asia|
|Luohe-Crossing||1989||China||?||202.5 m||pylons of reinforced concrete|
|380kV Thames Crossing||1965||UK||West Thurrock||190 m|
|Elbe Crossing 1||1958-1962||Germany||Stade||189 m|
|Bosporus overhead line crossing III||1999||Turkey||Istanbul||160 m|
|Pylons of Cadiz||1955||Spain||Cadiz||158 m|
|Aust Severn Powerline Crossing||?||UK||Aust||148.75 m|
|132kV Thames Crossing||1932||UK||West Thurrock||148.4 m||demolished in 1987|
|Karmsundet Powerline Crossing||?||Norway||Karmsundet||143.5 m|
|Limfjorden Overhead powerline crossing 2||?||Denmark||Raerup||141.7 m|
|Pylons of Voerde||1926||Germany||Voerde||138 m|
|Köhlbrand Powerline Crossing||?||Germany||Hamburg||138 m|
|Bremen-Farge Weser Powerline Crossing||?||Germany||Bremen||135 m|
|Pylons of Ghesm Crossing||1984||Iran||Strait of Ghesm||130 m||One pylon standing on a caisson in the sea|
|Shukhov tower on the Oka River||1929||Russia||Dzerzhinsk||128 m||Hyperboloid structure|
|Tarchomin-Lomianki Vistula Powerline Crossing||?||Poland||Tarchomin-Lomianki||127 m (Tarchomin), 121 m (Lomianki)|
|Skolwin-Inoujście Odra Powerline Crossing||?||Poland||Skolwin-Inoujście||126 m (Skolwin), 125 m (Inoujście)|
|Enerhodar Dnipro Powerline Crossing 2||1984||Ukraine||Enerhodar||126 m||Pylons on caissons|
|Bosporus overhead line crossing I||1957||Turkey||Istanbul||?|
|Bosporus overhead line crossing II||1983||Turkey||Istanbul||?|
|Little Belt Overhead powerline crossing 2||?||Denmark||Middelfart||125.3 m + 119.2 m|
|Duisburg-Wanheim Powerline Rhine Crossing||?||Germany||Duisburg||122 m|
|Little Belt Overhead powerline crossing 1||?||Denmark||Middelfart||119.5 m + 113.1 m|
|Pylons of Duisburg-Rheinhausen||1926||Germany||Duisburg-Rheinhausen||118.8 m|
|Bullenhausen Elbe Powerline Crossing||?||Germany||Bullenhausen||117 m|
|Lubaniew-Bobrowniki Vistula Powerline Crossing||?||Poland||Lubaniew/Bobrowniki||117 m|
|Ostrówek-Tursko Vistula Powerline Crossing||?||Poland||Ostrówek/Tursko||115 m|
|Bremen-Industriehafen Weser Powerline Crossing||?||Germany||Bremen||111 m||two parallel running powerlines, one used for traction current. Highest pylons designed for single phase AC use.|
|Nowy Bógpomóż-Probostwo Dolne Vistula Powerline Crossing||?||Poland||Nowy Bógpomóż/Probostwo Dolne||111 m (Probostwo Dolne), 109 m (Nowy Bógpomóż)|
|Daugava Powerline Crossing||1975||Latvia||Riga||110 m|
|Regów Gołąb Vistula Powerline Crossing||?||Poland||Regów/Gołąb||108 m|
|Orsoy Rhine Crossing||?||Germany||Orsoy||105 m|
|Limfjorden Overhead powerline crossing 1||?||Denmark||Raerup||101.2 m|
|Enerhodar Dnipro Powerline Crossing 1||1977||Ukraine||Enerhodar||100 m||Pylons on caissons|
|380kV-Ems-Overhead Powerline Crossing||?||Germany||Mark (south of Weener)||84 m|
|Pylon in the artificial lake of Santa Maria||1959||Switzerland||Lake of Santa Maria||75 m||Pylon in an artificial lake|
|Eyachtal Span||1992||Germany||Höfen||70 m||Longest span of Germany (1444 metres)|
|Pylon 1 of powerline departing Reuter West Power Station||?||Germany||Berlin||66 m||Chimney-like pylon with lattice steel crossbars|
|Pylon 310 of powerline Innertkirchen-Littau-Mettlen||1990||Switzerland||Littau||59,5 m||Tallest pylon of prefabricated concrete|
|Anlage 2610, Mast 69||?||Germany||Bochum||47 m||Pylon of 220kV-powerline decorated with balls in Ruhr-Park mall.|
|Colossus of Eislingen||1980||Germany||Eislingen/Fils||47 m||Pylon standing over a little river|
|Huddersfield Narrow Canal Pylon||?||UK||Stalybridge||?||Pylon standing over Huddersfield Narrow Canal, perhaps the only pylon whose legs can be passed under by boat|