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Pylons are used in suspension bridges and in electric power transmission networks. This article is about the latter.

A pylon is a lattice steel structure used to support overhead electricity conductors for power transmission.

If the pylon is just one in a continuous chain it is termed a suspension pylon as the conductors can be held by suspending them on vertical strings of insulators. Pylons at which sections of conductor start, finish or change direction are called strainer pylons. They may need anchor wires to counterbalance the weight of the conductors on the opposite side or be designed to deal with the forces imposed on them. The conductors are supported by horizontal strings of conductors.

Depending upon the voltage of the overhead line, different types of pylons are used.

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

A chain of pylons carry electricity conductors down the Longdendale Valley to Manchester. The first pylon is a strainer and the others are suspension pylons.

Pylons for high and extra-high voltages

For high and extra-high voltage lines (50kV and above), three phase systems are used. The pylons must therefore be designed for carrying 3 (or multiples of 3 if they carry several electric circuits) conductors. The towers are invariably steel (lattice/truss) (wooden structures are used in Germany in exceptional cases) and the insulators are generally glass disc insulators assembled in strings whose length is determined by the line voltage and environmental conditions.

An earth wire for lightning protection is often used, and for increased protection there are often two wires mounted at the top of each pylon.

In Germany and other countries, pylons for high and extra-high voltage are usually designed to carry 2 or more electric circuits. An electric circuit has three phases and hence 3 conductors. A single circuit line has 3 conductors, a double circuit line has six conductors, and so on.

For double circuit lines in Germany, the "Danube" towers or more rarely the "fir tree" towers, "ton" towers or towers for one level arrangement of conductors 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 building the line. The subsequent installation of additional circuits is very common.

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.

Pylons for powerlines for railway traction

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 that traction lines are designed for 2 conductors (and/or multiples of 3, usually 4.8 or 12). As a rule, the pylons of railway traction lines carry two electric circuits, so they have 4 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 an 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 current lines two earth conductors are used.

Pylons for high voltage direct current transmission

High voltage direct current transmissions are either monopolar or bipolar systems. Because of this fact, monopolar or bipolar lines are used. With bipolar systems a conductor arrangement with one conductor on each site of the pylon is used. For single-pole high voltage direct current transmissions pylons with only one conductor cable can be used. In many cases however the pylons are designed for a later two-pole development of the line.

In these cases on both sites on the pylon the conductor cables are installed for static reasons, where the second pole is either used until the installation of the second pole as line to the grounding electrode or joined in parallel with the other pole.In latter case the line from the converter station to the grounding electrode is built as underground cable. In two-pole overhead lines for high voltage direct current transmission the line to the grounding electrode can take over the function of the ground conductor, becuse it is grounded. In addition, it can be implemented as additional conductor. Pylons for high voltage direct current transmissions are usually equipped with one, sometimes also with two ground conductors.

Assembly

The lattice masts are arranged in a symmetrical pattern.

Lattice towers can be assembled lying on the ground and be put up by means of push pull cable but this method is rarely used because of the large assembly area needed. More frequently lattice masts are built up with the aid of a crane. High voltage masts in inaccessible places, like the mountains, are installed with helicopters.

Static tests

For testing the strength and endurance of pylons there are special test stations, in which pylons can be assembled and tested.

Special designs

Occasionally on pylons (in particular on steel framework masts for the highest voltage levels) antennas for low power UKW radio and television stations and for mobile phone services or radio systems are installed. On the mast of the Elbe crossing in Germany there is a radar facility of the water and shipping office Hamburg.

For the crossing of broad valleys and rivers there is sometimes a requirement for larger cable spacing to reduce the possibility of two cables colliding. In these cases one pylon per conductor may be used. Two well-known crossings of broad rivers are the Elbe crossing 1 and Elbe crossing 2 in Germany. The latter has the highest pylons in the world at 227 meters. The pylons crossing the Bay of Cadiz, Spain are 158 meters high.

Special locations

The Huddersfield Narrow Canal runs under the feet of a pylon. In the artificial lake of Santa Maria in Switzerland a 47 metre high anchor pylon for one circuit of a 380 kV-line was built on 28 metres high concrete columns

Pylons of special interest

• Pink Pylon
• Overhead line crossing Suez Canal
• Bosporus overhead line crossing I
• Bosporus overhead line crossing II
• Bosporus overhead line crossing III
• Pylons of Pearl River Crossing
• Pylons of Ghesm Crossing
• Pylons of Messina
• Pylons of Cadiz
• Elbe crossing 1
• Elbe crossing 2
• Pylons of Duisburg-Rheinhausen (220kV/110kV Rhine-crossing at Duisburg-Rheinhausen)
• Pylons of Voerde(220kV Rhine-crossing at Voerde)
• Pylon in the artificial lake of Santa Maria
• Colossus of Eislingen
• Sognefjord Span
• Eyachtal Span
• Ameralik Span

Types of pylon

Specific functions

• support pylon
• anchor pylon
• long distance anchor pylon
• twisting pylon
• branch pylon
• anchor portal
• termination pylon
• pylon transformer
• switch pylon

Materials used

• wood pylon
• concrete pylon
• steel tube pylon
• lattice steel pylon

Conductor arrangements

• portal pylon
• delta pylon
• single-level pylon
• two-level pylon
• three level pylon
• ton pylon
• pine pylon

Specific locations

• roof stand
• crossing pylon

Specific purposes

• rail current pylon
• hybrid pylon
• overhead line pylon
• telephone pole

External links

• Flash Wilson's pylon photo gallery and pylon FAQ (http://www.gorge.org/pylons)
• Pictures of Pylons (http://users.castel.nl/~berka01/home.htm)
• Remarkable Pylons (http://www.structurae.de/en/structures/ftype/f2018.cfm)

de: Freileitungsmast