- This article or section should include material from Support pylon
- This article has been machine translated.
- 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 horizontally on the ground and erected by push-pull cable, but this method is rarely used because of the large assembly area needed. Lattice masts are more usually built using a crane. High voltage masts more inaccessible areas are installed using 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 Antennas for low power UKW radio, television, and mobile phone services or radio systems are sometimes erected on pylons, especially on the steel masts carrying high voltage cables. There is a radar facility for the Hamburg water and shipping office on the mast of the Elbe crossing in Germany.
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 the world, at 227 metres. The pylons crossing the Bay of Cadiz, Spain are 158 meters high.
Special locations The Huddersfield Narrow Canal runs between 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 is constructed on 28-metre-high concrete columns.
Pylons of special interest
Types of pylon
Specific functions
Materials used
Conductor arrangements
Specific locations
Specific purposes
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