Pylon
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A pylon is a construction for the support of an electrical overhead line. If the pylon is just one in a continuous chain it is termed a carrying pylon. Pylons at which sections of conductor cables start or finish are called guyed pylons, as they need guy wires to apply support equal to the weight of the conductors on the opposite side. Other pylon types are branch pylons for where a line branches and there are special varieties of a carrying Pylon where cables sections start and finish.
Depending upon the electrical voltage of the overhead line different pylon types are used.
Pylons for lines for data transmission
Pylons for low-voltage (Operating voltage up to 1000 V)
In low-voltage systems, three-phase AC systems are always used operating as a four conductor (Wye) system (the neutral conductor is always implemented as a separate conductor). There are also two-conductor branch lines for the supply to individual houses with single phase AC-current. The most frequent arrangement of these conductor cables is in two levels (2 on the highest, 2 on the lowest crossbar). Three-phase alternating current overhead lines within the low-voltage range normally carry only one electric circuit. If two electric circuits are run in parallel on a pylon, the two-level arrangement is usually used, whereby each mast half carries an electric circuit. Insulators are usually standing on the crossbeams, more rarely hanging types are used. The pylons are often wood or concrete with metal crossbeams. Frequently low-voltage overhead lines are also mounted on small pylons of steel tube on the building roofs. Two-conductor low-voltage lines have a conductor cable for positive and one for neutral.
Two-conductor overhead lines are used occasionally for the supply of street lamps. These lamps are always designed for single phase power connections. These are fastened either to the lamp masts at height of the lights or led to hanging constructions over the road, on which the lamps hang. There is often the requirement to run the road lighting in full and in half intensity. In this cases an additional line must be used, so that such a line system has 3 conductor cables. Ground conductors are not used with overhead lines for operating voltages under 1000 V.
Overhead line masts for medium voltage (1kV to 50kV)
In this voltage level three conductor systems (Delta) are always used. This saves on conductors and reduces costs for long lines. Conversion to lower voltages for local distribution requires a delta to wye step-down transformer and careful balancing of the loads.
The masts are usually wood, sometimes steel tube or concrete masts. Sometimes such lines can share masts for high voltage (110kV), usually on the lowest crossarm. In carry heavier cables. In principle, not all electric circuits need to be installed initially when the line is built. An additional installation of extra electric circuits at a later time is very common. As insulators either standing or hanging types can be used. The former makes the cable higher but increases the danger of lightning strikes. The latters result in less chance of lightning strikes. Earth wires are used with overhead line masts for medium voltage nets only in exceptional cases. A special characteristic of lines in this voltage range are transformers and overhead line switches, which are mounted on the pylons, operated by a rod from some position at the foot of the pylon.
Pylons for high and extra-high voltage lines (50kV and more)
As in the medium voltage level for three-phase current systems, three conductor systems are used. The pylons must therefore be designed for carrying 3 (or multiples of 3 if they carry several electric circuits) conductors. Insulators of the hanging type are always used. The masts are invariably steel framework masts (lattice masts). Wood masts are used in Germany only in exceptional cases. An earth wire for the lightning protection is often used. For increased lightning protection the are often two groundwires mounted at top of the highest crossarm, a separate crossarm on the top of the pylon over the conductors or one on each of a pylons with V-shaped tops.
In Germany pylons for high and extra-high voltage are usually designed for carrying 2 or more electric circuits. For 2 electric circuits in Germany the Danube mas or more rarely the fir tree mast, ton mast or mast for one level arrangement of conductors are usually used. On pylons for several current ciruits it is not necessary to install all electric circuits at the time of building pylons. The practice of later installation of individual electric circuits is very common. Frequently on pylons for 110kV-lines also medium voltage lines are run parallel to them. A parallel circuit of 380kV, 220kV and 110kV-lines on the same pylon is common. Sometimes, especially with 110kV-circuits a parallel circuit provides traction current lines.
Pylons for powerlines for railway traction
Pylons for overhead line for single phase AC-current for railway traction correspond to pylons for 110kV-three phase AC current in their construction. Steel framework masts, rare steel tube or concrete pylons are usually used. However railway traction current systems are two-pole alternating current systems, so that traction current pylons must be laid out for the admission of 2 conductor cables (and/or an integral multiples of it, usually 4.8 or 12). As a rule the pylons of railway traction current lines carry two electric circuits, so they possess 4 conductor cables. These are usually arranged in one level, whereby each circuit occupies one half of the crossbar. For four traction current circuits the arrangement of the conductors in two-levels and for six electric circuits the arrangement of the conductors in three levels is used. Under narrow space conditions, it is also possible to arrange the conductors of one traction current circuit in two levels. Running a traction current power line parallel to a high voltage transmission lines for three-phase alternating current is possible. Therefore usually a separate cross arm on the pylon is used. If traction current lines are led parallel to 380kV-lines, its insulation must be gesigned for 220kV, because in the event of an error dangerous overvoltages to the three-phase alternating current line can occur. Traction current overhead lines are usually equipped with one earth conductor. In Austria on some traction current lines two ground 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
Pylons made of wood or concrete are delivered as a rule as a whole and put up at the place of assembly. This applies also to stahlrohrmaste. Also lattice masts can be assembled lying and be put up then by means of push pull cable. Although this procedure is still interesting because of the reduction of work in larger height also today, it is hardly still used as a rule because of the necessary assembling place. More frequently lattice masts come to a hold, there is called built up with the help of a small crane, which is fastened to the construction, piece for piece. Besides becomes, in particular if the mast assembly is to take place within a short time, because for example a mast of a line is to be replaced and be switched off this line only on weekend can also with the help of a crane installed. High voltage masts in inaccessible places, like in the mountains, are installed oh with helicopters. It is to be increased also usually lattice masts by using further elements in its height, in order to increase for example the line height for building projects under the line. Such work is usually accomplished with a crane, sometimes also with a helicopter.
Statical tests
For testing of statical properties of pylons there there are special test stations, in which pylons can be assembled and tested of their statical properties.
Special designs
For the realization of branches sometimes quite impressive constructions must be built. This applies also pylons for conductor drilling when conductors are arranged in three levels. Occasionally on pylons (in particular on steel framework masts for the highest voltage levels) also transmitting plants are installed. Usually these are installations for mobile phone services or the radio systems of the power supply company, occasionally however for other radio services. Thus transmitting antennas for low power UKW radio and television stations were already installed on pylons. On the carrying mast of the Elbe crossing 1 there is a radar facility of the water and shipping office Hamburg.
For the crossing of broad valleys there must be a large distance between the conductor cables, so that this also with storm cannot to together-strike and cause a short-circuit. In these cases occasionally for each conductor one pylon is used. For the crossing of broad rivers and straits very pylons must be built at flat coastal topography, because shipping requires a large passage height. Such pylons must be equipped with flight safety lamps. They possess frequently also for maintenance of these installations stairs and gangways with railings. Two well-known crossings of broad rivers are the Elbe crossing 1 and Elbe crossing 2. The latter has the highest pylons of the earth (height: 227 meters). From particularly interest are the constructions of the pylons built in the 50's for the powerline crossing the bay of Cadiz, Spain. They are two 158 meters high pylons with one cross beam, consisting of an impressive kegelstumpffoermigen framework construction.
Special locations of pylon foundations
If the culture-geographical conditions require it, then overhead line masts are built also at unusual locations. Thus pylons standing with their feet over small rivers were already built. In the artificial lake of Santa Maria in Switzerland a 47 meter high anchor pylon for one circuit of a 380kV-line was built on 28 meters high concrete columns. (Pylon in the artificial lake of Santa Maria).
Kinds of pylons
Name after function
- support pylon
- anchor pylon
- long distance anchor pylon
- twisting pylon
- branch pylon
- anchor portal
- termination pylon
- pylon transformer
- switch pylon
Name after used material
- wood pylon
- concrete pylon
- steel tube pylon
- lattice steel pylon
Name after arrangment of conductors
- portal pylon
- delta pylon
- single-level pylon
- two-level pylon
- three level pylon
- ton pylon
- pine pylon
Name after location
- roof stand
Name after purpose
- rail current pylon
- hybrid pylon
- overhead line pylon
- telephone pole
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