Science Fair Project Encyclopedia
Electricity pylon
- Pylons are used in suspension bridges and in electric power transmission networks. This article is about the latter.
A pylon is a tall steel lattice structure used to support overhead electricity conductors for power transmission.
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High voltage AC transmission pylons
Three-phase 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 DC transmission pylons
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, only pylons with 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 (because of static electricity). 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.
Railway traction line pylons
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 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 circuits, two earth conductors are used.
Assembly
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
Testing of statical properties
There are special facilities for testing the statical properties of pylons (and perhaps other types of lattice towers)
Special designs
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.
When spanning broad valleys, larger cable spacing is sometimes necessary to reduce the possibility of cables touching. 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 uses the highest pylons in Europe, at 227 metres. The pylons crossing the Bay of Cadiz, Spain are 158 meters high.
Types of pylons
Specific functions
- anchor pylons (or strainer pylons) utilize horizontal insulators and occur at the endpoints of conductors.
- Support pylons (or suspension pylons) occur along the route of a conductor between anchor pylons, and keep the conductor suspended with vertical strings of insulators.
- Twisting pylons are anchor pylons at which the conductors are "twisted" so that they exchange sides of the pylon.
- long distance anchor pylon
- branch pylon
- anchor portal
- termination pylon
- switch pylon
Materials used
Conductor arrangements
Specific locations
Specific purposes
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
External links
- Flash Wilson's pylon photo gallery and pylon FAQ
- Pictures of Pylons
- Remarkable Pylons
- Pylon of the month page
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