Electricity pylon
A
pylon is a tall steel lattice
structure used to
support overhead electricity conductors for
power transmission. In
American English, these are known as
transmission towers or
masts.
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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 |
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A chain of pylons carry electricity conductors down the Longdendale Valley to Manchester. The first pylon is a strainer. The others are suspension pylons. |
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A solitary pylon near the Shen-Shan Highway in Guangdong |
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 at the top of each pylon.
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 more rarely, the "
fir tree" towers, are usually used. If a line is constructed using pylons designed to carry several circuits, it is not necessary to install all the circuits at the time of construction.
Medium voltage circuits are often erected on the same pylons as 110 kV lines. Paralleling circuits of 380 kV, 220 kV and 110 kV-lines on the same pylons 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 pylon is used. For single-pole HVDC transmission with ground return, pylons with only one conductor cable can be used. In many cases, however, the pylons are designed for later conversion to a two-pole system. In these cases, conductor cables are installed on both sides of the pylon 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.
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Twisting pylon of powerline for single phase AC traction current ( 110kV, 16.67 Hertz) near Bartholomä in Germany |
Pylons used for single phase AC
railway traction lines are similar in construction to pylons 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 pylons 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 pylons 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.
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The lattice masts are arranged in a symmetrical pattern. |
Lattice towers can be assembled horizontally on the ground and erected by push-pull cable, but this method is rarely used because of the large assembly area needed. Lattice towers are more usually erected using a crane or, in inaccessible areas, a helicopter.
There are
tower testing stations for testing the mechanical properties of pylons.
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Pylon Identification Tag on HVAC anchor pylon at Dorsey Converter Station near Rosser, Manitoba â€" August, 2005 |
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Pylons of the powerline crossing the Bay of Cádiz in Spain |
Besides the obligatory high voltage warning sign, electricity pylons also frequently possess a sign with the names of the line (either the terminal points of the line or the internal designation of the EVU) and the pylon number. This makes it easier posting a fault to the power company, who belongs the pylon.
In some countries electricity pylons of lattice steel have to be equipped with some barbe wire stripes approximately 3 metres above ground in order to avoid unauthorized climbing of them. Such devices can be also found at pylones in countries where this is not the law in the proximity of festival sites or roads.
Antennas for low power
FM radio,
television, and mobile phone services are sometimes erected on pylons, especially on the steel masts carrying high voltage cables.
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 4597 meters) and the Ameralik span in Greenland (span width: 5376 meters). In Germany the overhead line of the EnBW AG crossing of the Eyachtal has the largest span, a width of 1444 meters.
In order to drop overhead lines into steep, deep valleys, inclined pylons are occasionally used. One finds such masts 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 380kV 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 conductor cables of the outgoing lines. Because of possible problems with corrosion by the flue gases, such constructions are very rare.
Specific functions
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anchor pylons (or strainer pylons) utilize horizontal insulators and occur at the endpoints of
conductors.
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pine pylon â€" an electricity pylon for two circuits of
three-phase AC current, a which the
conductors are arranged in three levels. In pine pylons the lowest crossbar has a wider span than that in the middle and this one a larger span than that on the top.
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Twisting pylons are anchor pylons at which the conductors are "twisted" so that they exchange sides of the pylon.
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long distance anchor pylon*
branch pylon*
anchor portal*
termination pylon*
switch pylonMaterials used
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wood pylon*
concrete pylon*
steel tube pylon*
lattice steel pylon*
concrete filled steel tube pylonConductor arrangements
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portal pylon*
delta pylon*
single-level pylon*
two-level pylon*
three level pylon*
Barrel pylonSpecific locations
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roof stand*
crossing pylonSpecific purposes
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rail current pylon*
hybrid pylon*
telephone pole*
Lattice tower*
Flash Wilson's pylon photo gallery and pylon FAQ*
Pictures of Pylons and technical information*
Remarkable Pylons*
Pylon of the month page*
Power Station Konakovskaya GRES, at which chimneys serve as electricity pylons
