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Encyclopedia > Overhead lines
The overhead lines of a Swiss Federal Railways track.

Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point. These overhead lines are known variously as Image File history File links Download high-resolution version (1623x1623, 506 KB) Summary Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Overhead lines ... Image File history File links Download high-resolution version (1623x1623, 506 KB) Summary Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Overhead lines ... Swiss Federal Railways (SBB-CFF-FFS) is the national railway company of Switzerland. ... Electrical energy can refer to several closely related things. ... A CLRV Streetcar in the City of Toronto. ... Å koda 14 Tr trolleybus in Vilnius, Lithuania. ... This article is about trains in rail transport. ...

  • OCS (overhead contact system – US & Europe, except UK)
  • OLE or OHLE (overhead line equipment – UK)
  • OHW (overhead wiring – AUS) or
  • Catenary (somewhat inaccurately).

For the purposes of this article the generic term overhead line has been used.


Overhead line is designed on the principle of one or more overhead wires situated over rail tracks, raised to a high electrical potential by connection to feeder stations at regular intervals. The feeder stations are usually fed from a high-voltage electrical grid. Rail tracks. ... In electrical engineering High voltage refers to a voltage which is high. ... This is an 11kV/400V-230V transformer in an older suburb of Wellington, New Zealand Electricity distribution is the penultimate stage in the delivery (before retail) of electricity to end users. ...

Contents

Overview

Electric trains that collect their current from overhead line system use a device such as pantograph, bow collector, or trolley pole. The current collection device presses against the underside of the lowest wire of an overhead line system, which is called a contact wire. The current collectors are electrically conductive, and allow current to flow through to the traction motors of the train or tram, and back to the feeder station via the steel wheels and one or both running rails of the track. Diesel trains may pass along these tracks without affecting the overhead line, although overhead clearance may be an issue. A pantograph is a device that collects electric current from overhead lines for electric trains or trams. ... An old tram with a bow collector built in 1907 still running in Oberbozen, South Tyrol, Italy A bow collector is one of the three main devices used on tramcars to transfer electric current from the wires above to the tram below, the other devices being the pantograph and trolley... Trolley poles are usually tapered cylindrical poles of wood or metal, used to transfer electricity from a live overhead wire to the control and propulsion equipment of a trolley car, tram or trolley bus. ... Rudolf Christian Karl Diesel (1858-1913), inventor of the diesel engine. ...


Construction

Linemen on a Maintenance of way vehicle repairing overhead lines.

Because they run on rubber wheels running on pavement rather than steel wheels running on steel rails, trolleybuses must have a second trolley pole contacting a second wire to return the current to the power system. Image File history File linksMetadata Download high resolution version (768x1024, 390 KB) pociąg sieciowy pod Łowiczem autorem zdjęcia jest PrzemD File links The following pages link to this file: Overhead lines Lineman (occupation) Metadata This file contains additional information, probably added from the digital camera or scanner used... Image File history File linksMetadata Download high resolution version (768x1024, 390 KB) pociąg sieciowy pod Łowiczem autorem zdjęcia jest PrzemD File links The following pages link to this file: Overhead lines Lineman (occupation) Metadata This file contains additional information, probably added from the digital camera or scanner used... Linemen repairing overhead lines (that supply power to trains) Linemen repairing electricity distribution lines (that supply power to homes) A lineman or linesman is a tradesman who constructs and maintains electric power transmission and distribution facilities. ... Maintenance of way (often abbreviated as M of Way, MOW or MW) refers to the maintenance of railroad rights of way. ... Škoda 14 Tr trolleybus in Vilnius, Lithuania. ...


To achieve good high speed current collection, it is necessary to keep the contact wire geometry within defined limits throughout the length of the overhead line. It is usually achieved by supporting the contact wire from above by means of a second wire, known variously as the messenger wire (US & Europe) or catenary (UK & Canada). This wire is allowed to follow the natural path of a wire strung between two points, which is known as a catenary curve, thus the use of catenary to describe this wire or sometimes the whole system. This wire is attached to the contact wire at regular intervals by vertical wires known as droppers or drop wires. In this way the contact wire is effectively supported at numerous points. The messenger wire is supported regularly at structures, either by means of a pulley, link, or clamp. The whole system is then subjected to a mechanical tension. The messenger wire is usually pulled slightly to the left and right by successive supports, so that the contact wire slides from side to side on the pantograph as the vehicle moves along (if it did not then it would tend to wear a groove in the pantograph's carbon insert). Such a system, with a single supporting wire, is known as simple equipment. In mathematics, the catenary is the shape of a hanging flexible chain or cable when supported at its ends and acted upon by a uniform gravitational force (its own weight). ... Pulleys on a ship. ... A clamp is a fastening device to hold or secure objects tightly together to prevent movement or separation through the application of inward pressure. ... Tension is a reaction force applied by a stretched string (rope or a similar object) on the objects which stretch it. ...


When overhead line systems were first conceived, good current collection was not possible at high speed using a single supporting wire. Two additional types of equipment were developed to combat this problem. Stitched equipment used an additional wire at each support structure, which was terminated either side to the messenger wire. Compound equipment used a second support wire, known as the auxiliary, running the whole length of the overhead line between the messenger wire and the contact wire. Droppers are provided to support the auxiliary from the messenger wire, and additional droppers support the contact wire from the auxiliary.


The dropper wires usually only provide physical support of the contact wire, and do not join the catenary and contact wires electrically. Separate wires are provided for this function.


Another reason to use an auxiliary wire is that such a wire could be constructed of a more conductive but less wear-resistant metal, increasing the efficiency of power transmission.


For tramways there often is just a simple contact wire and no messenger wire. A CLRV Streetcar in the City of Toronto. ...


Tensioning

For medium and high speeds the wires are generally tensioned by means of weights, or occasionally by hydraulic tensioners. Either method is known as auto-tensioning (AT), and ensures that the tension in the equipment is virtually independent of temperature. Tensions are typically between 9 and 20 kN per wire. The newton (symbol: N) is the SI unit of force. ...


For low speeds and in tunnels where temperatures are constant, fixed termination (FT) equipment may be used, with the wires terminated directly on structures at each end of the overhead line. Here the tension is generally about 10 kN. This type of equipment will sag on hot days and hog on cold days.


Where AT is used, there is a limit to the continuous length of overhead line which may be installed. This is due to the change in the position of the weights with temperature as the overhead line expands and contracts. This movement is proportional to the tension length, i.e. the distance between anchors. This leads to the concept of maximum tension length. For most 25 kV OHL equipment in the UK the maximum tension length is 1970 m.


An additional issue with AT equipment is that, if balance weights are attached to each end, the whole tension length will be free to move along track. Therefore, a mid-point anchor (MPA) is introducing close to the centre of the tension length to restrict movement. MPAs are often fixed to low bridges.


Therefore a tension length can be seen as a fixed centre point with the two half tension lengths expanding and contracting with temperature.


Breaks

To allow maintenance to sections of the overhead line without having to turn off the entire system, the overhead line system is broken into electrically separated portions known as sections. Sections often correspond with tension lengths as described above. The transition from section to section is known as a section break and is set up so that the locomotive's pantograph is in continuous contact with the wire. Great Western Railway No. ...


For bow-collectors and pantographs, this is done by having two contact wires run next to each other over a length about four wire supports: a new one dropping down and the old one rising up until the pantograph smoothly transfers from one to the next. The two wires never touch (although the bow-collector/pantograph is briefly in contact with both wires). In normal service the two sections are electrically connected (to different substations if at or near the halfway mark between them), but this can be broken for servicing.


On overhead wires designed for trolley poles this is done by having a neutral section between the wires, but this requires an insulator. The driver of the tram or trolleybus must turn off the power when the trolley pole passes through to prevent arcing causing damage to the insulator. A CLRV Streetcar in the City of Toronto. ... Å koda 14 Tr trolleybus in Vilnius, Lithuania. ...


Sometimes on a larger electrified railway, tramway or trolleybus system it is necessary to power different areas of track from different power grids, the synchronisation of the phases of which cannot be guaranteed. (Indeed, sometimes the sections are even powered with different voltages or frequencies) There may be mechanisms for having the grids synchronised on a normal basis, but events may cause desynchronisation. This is no problem for DC systems, but for AC systems it would obviously be quite undesirable to connect two unsynchronised grids together, even momentarily. A normal section break is insufficient to guard against this since the pantograph briefly connects both sections.


Instead, a phase break or neutral section is used. This consists of two section breaks back-to-back so that there is a short section of overhead line that belongs to neither grid. If the two grids are synchronised, this stretch of line is energised (by either supply) and trains run over it normally. If the two supplies are not synchronised, the short isolating section is disconnected from the supplies, leaving it electrically dead, ensuring that the two grids cannot be connected to each other.


The sudden loss of power over the phase break would jar the train if the locomotive was at full throttle, so special signals are set up to warn the crew. When synchronization is lost and the phase break is deenergised, the train's operator must put the controller (throttle) into neutral and coast through an isolated phase break section.


On the Pennsylvania Railroad, phase breaks were indicated to train crews by a metal sign hung from the overhead with the letters PB on it, created by holes drilled in the metal. When the phase break was "dead", a signal consisting of eight lit lights in a circular pattern indicated this to the crew. 1893 map The Pennsylvania Railroad (AAR reporting mark PRR) was an American railroad that was founded in 1846 and merged in 1968 into Penn Central Transportation. ...


Crossings

An annotated version of the above.Blue = tram conductorGreen = trolley bus wiresYellow = insulated trough
An annotated version of the above.
Blue = tram conductor
Green = trolley bus wires
Yellow = insulated trough

Trams draw their power from a single overhead wire at about 500 to 750 V above earth, while trolleybuses draw their power from two overhead wires (powered at similar voltage). Because of that, at least one of the trolleybus wires must be insulated from tram wires. This is usually solved in the following way: the trolleybus wires run continuously through the crossing. The tram conductors are slung a few centimetres lower than the trolleybus wires. Close to the junction on each side, the wire merges into a solid bar which is angled to run parallel to the trolleybus wires for about half a metre. Another bar similarly angled at its ends is hung between the trolleybus wires. This is electrically connected above to the tram wire's catenary cable. The tram's pantograph bridges the gap between the different conductors, providing it with a continuous pickup. Wikipedia does not have an article with this exact name. ... Wikipedia does not have an article with this exact name. ... A CLRV Streetcar in the City of Toronto. ... The volt is the SI derived unit for electric potential and voltage (derived from the ampere and watt). ... Ground symbols The term ground or earth usually means a common return path in electrical circuits. ... Å koda 14 Tr trolleybus in Vilnius, Lithuania. ... In science and engineering, conductors are materials that readily conduct electric current through electrical conduction. ... Catenary is a system of overhead wires used to supply electrical power to a locomotive, streetcar, or light rail vehicle. ...


Where the tram wire crosses, the trolleybus wires are protected by an inverted trough of insulating material extending 20 or 30 mm below the level of the trolleybus wires. The tram pantograph or bow collector raises the conductor wire a little as it passes under. These troughs are presumably to limit how far it can do that and to provide a backstop to prevent the tram pantograph or bow collector ever touching the trolleybus wires. This article or section is in need of attention from an expert on the subject. ...


Another system that has been used is to coincide section breaks with the crossing point so that the crossing is electrically dead.


It can also be noted that in some cities, trolleybuses and trams have shared the same positive (feed) wire. In such cases a normal trolleybus frog can be used. In Stockholm, Sweden there was until 1946 a level crossing between the railway south of Stockholm Central Station and a tramway line. The tramway operated on 600-700 V DC and the railway operated on 15 kV AC. Some crossings between tramway/light rail and railways are still alive in Germany. Å koda 14 Tr trolleybus in Vilnius, Lithuania. ... A CLRV Streetcar in the City of Toronto. ...   (IPA: ; UN/LOCODE: SE STO) is the capital of Sweden, and consequently the site of its Government and Parliament as well as the residence of the Swedish head of state, King Carl XVI Gustaf. ... A CLRV Streetcar in the City of Toronto. ... A twisting pylon of a single phase AC 110kV-powerline near Bartholomä in Germany. ...


Australia

Many cities, including Adelaide, South Australia, had trams and trolleybuses (Adelaide still has one tramline today) both using trolley pole current collection. They used insulated crossovers which required tram drivers to put the controller into neutral and coast through. Trolleybus drivers had to either lift off the accelerator or switch to auxiliary power. Adelaide is the capital and most populous city of the Australian state of South Australia, and is the fifth largest city in Australia, with a population of over 1. ... Capital Adelaide Government Constitutional monarchy Governor Marjorie Jackson-Nelson Premier Mike Rann (ALP) Federal representation  - House seats 11  - Senate seats 12 Gross State Product (2004-05)  - Product ($m)  $59,819 (5th)  - Product per capita  $38,838/person (7th) Population (End of March 2005)  - Population  1,540,200 (5th)  - Density  1. ... A depiction of one of the H-class Glenelg trams by Simon Lieschke. ...


In Melbourne, Victoria tram drivers are still required to put the controller into neutral and coast through section insulators, this being indicated to drivers by insulator markings between the rails. Melbournes Yarra River is a popular area for walking, jogging, cycling, rowing and for relaxing on the banks with a picnic Melbourne (pronounced ) is the second most populous city in Australia, with a metropolitan area population of approximately 3. ... Capital Melbourne Government Const. ...


Melbourne also has another interesting issue - crossings between electrified suburban railways and tram lines at grade. There are four of these level crossings through the systems and each requires complex switching arrangements to separate the operation of 1500 V DC overhead for the railway and 650 V DC for the trams. This is called an overhead square. Proposals have been put forward which would eventually see most or all of these crossings grade separated or the tram routes diverted. The term level crossing (also called a railroad crossing, railway crossing, train crossing or grade crossing) is a crossing on one level (at-grade intersection) — without recourse to a bridge or tunnel — of a railway line by a road, path, or another railroad. ...


Germany

A twisting pylon of a single phase AC 110 kV power line near Bartholomä in Germany. Lines of this type are used in Germany to supply electric railways with single phase AC with 16.7 hertz
A twisting pylon of a single phase AC 110 kV power line near Bartholomä in Germany. Lines of this type are used in Germany to supply electric railways with single phase AC with 16.7 hertz

In Germany there are special overhead power lines for single phase AC traction current with a frequency of 16.7 hertz. Most of these lines, which are all operated with a voltage of 110 kV have four conductor cables for two circuits. As a rule at traction current lines, the single-level arrangement of the conductor cables is used. A traction current pylon is a pylon with at least carry one electric circuit for traction current. For traction current lines with four circuits (eight conductor cables) frequently two-level arrangements of conductors are used, at which one crossbar carries four conductor cables. For traction current lines used for supplying new high-speed rail tracks, three-level arrangements of conductors are used. Thereby are on the lowest crossbar four, and on the upper crossbars two, conductor cables mounted. The three-level arrangement is also used for traction current lines with 6 electric circuits (12 conductor cables). There are further, in particular for the power supply of rapid transit railways operated with alternating current, overhead line pylons with crossbars for 110 kV traction current powerlines above the contact wire in use. There are also pylons that carry electric circuits for traction current and for three-phase alternating current of the public power grid. Image File history File linksMetadata Download high-resolution version (936x1764, 672 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Electric power transmission Overhead lines Railway electrification system Electricity pylon Anchor pylon 15 kV AC Metadata This file... Image File history File linksMetadata Download high-resolution version (936x1764, 672 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Electric power transmission Overhead lines Railway electrification system Electricity pylon Anchor pylon 15 kV AC Metadata This file... Electrical conduction is the movement of electrically charged particles through a transmission medium (electrical conductor). ... A pylon is a tall steel lattice structure used to support overhead electricity conductors for power transmission. ... In electricity, current refers to electric current, which is the flow of electric charge. ... For lower capacity public transit systems, see tram, light rail, bus, and bus rapid transit. ...


Greece

In Athens there are two crossings between overhead tram and trolleybus wires. These crossings are at the junction of Vas. Amalias Avenue with Vas. Olgas Avenue, and the junction of Ardittou Street with Athanasiou Diakou Street. They use the above-mentioned solution for crossing tram and trolleybus wires. Nickname: City of Athena or Cradle of Democracy Location of the city of Athens (red dot) within the Prefecture of Athens and Periphery of Attica Coordinates: Country Greece Peripheries Attica Prefecture Athens Founded circa 2000 BC Mayor Nikitas Kaklamanis Area    - City 38. ...


Additionally, for about one year (from the opening of the tram system in the summer of 2004 until mid-2005), trams and trolleybuses with direction to Pagrati shared the same exclusive lane on the far right side of Vas. Olgas Avenue (which is about 400 m long); this required tram and trolleybus wires to coexist side-by-side above a very narrow lane of road. To solve this problem, the trolleybus wires were placed on the far right of the lane, rendering it impossible for the tram's (very wide) pantograph to come into contact with them. As a side-effect, however, trolleybus drivers were required to employ much greater caution on this stretch of road, and drive very slowly through Vasilisis Olgas Avenue, owing to the trolleybus collectors being extended to their limits under this arrangement. Finally, a change of route for trolleybuses was implemented in mid-2005, avoiding Vas. Olgas Avenue completely, and ending this difficult coexistence.


Multiple overhead lines

There are and were some railways which used two and even three overhead lines, usually to carry three-phase current to the trains. Nowadays, three phase AC-current is used only on the Gornergrat Railway and Jungfraujoch Railway in Switzerland, the Petit Train de La Rhune in France and the Corcovado Rack Railway in Brasil; until 1976, it was widely used in Italy. On these railways the two conductors of the overhead lines are used for two different phases of the three-phase AC, while the rail was used for the third phase. The neutral was not used. Three phase systems have 3 waveforms (usually carrying power) that are 2/3π radians (120 degrees,1/3 of a cycle) offset in time. ... La Rhune (Basque: Larrun - pastureland) is a mountain (892m) at the western end of the Pyrenees. ... Corcovado Rack Railcar The Corcovado Rack Railway is a mountain railway line in the city of Rio de Janeiro in Brazil. ...


Some three-phase AC railways used three overhead wires. These were an experimental railway line of Siemens in Berlin-Lichtenberg in 1898 (length: 1.8 kilometres), the military railway between Marienfelde and Zossen between 1901 and 1904 (length: 23.4 kilometres) and an 800-metre-long section of a coal railway near Cologne, between 1940 and 1949.


On DC systems bipolar overhead lines were sometimes used to avoid galvanic corrosion of metallic parts near the railway. An example of a railway run with DC using two overhead lines was the Chemin de fer de la mure. The Galvanic cell, named after Luigi Galvani, consists of two metals connected by an electrolyte which forms a salt bridge between the metals. ... The Chemin de fer de la mure (the Railway of the Wall) is an electrified railway near Grenoble. ...


All systems of multiple overhead lines have the disadvantage of high risk of short circuits at switches and therefore tend to be impractical in use, especially when high voltages are used or when trains run through the points at high speed.


Overhead catenary

A catenary is a system of overhead wires used to supply electricity to a locomotive, streetcar, or light rail vehicle which is equipped with a pantograph. A wire is a single, usually cylindrical, elongated strand of drawn metal. ... Lightning strikes during a night-time thunderstorm. ... Great Western Railway No. ... a historic postcard showing electric trolley-powered streetcars in Richmond, Virginia, where Frank J. Sprague successfully demonstrated his new system on the hills in 1888 A streetcar is a railway vehicle designed to carry passengers on tracks, usually laid in city streets. ... This article is about light rail systems in general. ... A pantograph is a device that collects electric current from overhead lines for electric trains or trams. ...


Unlike simple overhead wires, in which the uninsulated wire or cable is attached by clamps to closely spaced crosswires, themselves supported by line poles, catenery system use at least two wires. One wire, called the catenary wire or the messenger wire, is hung at a specific tension value in the shape of a mathematical catenary between line structures. A second wire is held in tension by the messenger wire, to which it is attached at frequent intervals by clamps and connecting wires. The second wire is straight and level, parallel to the rail tracks, suspended over it as the roadway of a suspension bridge is over water. An electric multiple unit pulling into Tile Hill station; Coventry, England. ... 6 or 15cm outside diameter, oil-cooled cables, traversing the Grand Coulee Dam throughout. ... In mathematics, the catenary is the shape of a hanging flexible chain or cable when supported at its ends and acted upon by a uniform gravitational force (its own weight). ... Tension is a reaction force applied by a stretched string (rope or a similar object) on the objects which stretch it. ... A clamp is a fastening device to hold or secure objects tightly together to prevent movement or separation through the application of inward pressure. ... Railroad or railway tracks are used on railways, which, together with railroad switches (points), guide trains without the need for steering. ... A suspension bridge is a type of bridge that has been made since ancient times as early as CE 100. ...


Simple wire installations are common in light rail applications, especially on city streets, while more expensive catenery systems are especially suited to high-speed operations. The city of Chicago, as seen from the sky The main square of the Catalan city of Sabadell during a popular celebration. ... A city-centre street in Frankfurt, Germany A residential street in Cambridge, Massachusetts, USA A street is a public thoroughfare in the built environment. ...


The Northeast Corridor in the United States features electrified catenary over a 600-mile or 1000 km distance between Boston, Massachusetts and Washington, D.C., providing power for Amtrak's high-speed Acela Express and other trains. Several commuter rail agencies, including MARC, SEPTA, NJ Transit, Metro-North utilize the catenary to provide local service along the Northeast Corridor. Most of the NEC (those sections shown in red, except Boston to the Rhode Island state line) is owned by Amtrak. ... Nickname: City on the Hill, Beantown, The Hub (of the Universe)1, Athens of America, The Cradle of Revolution, Puritan City, Americas Walking City Location in Massachusetts, USA Counties Suffolk County Mayor Thomas M. Menino(D) Area    - City 232. ... This article is about the U.S. State. ... Nickname: DC, The District Motto: Justitia Omnibus (Justice for All) Location of Washington, D.C., in relation to the states Maryland and Virginia Coordinates: Federal District District of Columbia  - Mayor Adrian M. Fenty (D)  - City Council Chairperson: Vincent C. Gray (D) Ward 1: Jim Graham (D) Ward 2: Jack Evans... Acela Express in West Windsor, NJ Amtrak Cascades service with tilting Talgo trainsets in Seattle, Washington Amtrak train in downtown Orlando, Florida For other uses, see Amtrak (disambiguation). ... Acela Express (often called simply Acela, leading to early confusion with the Acela Regional and Acela Commuter) is the name used by Amtrak for the high-speed tilting train service operating between Washington, D.C. and Boston via New York City and Philadelphia along the Northeast Corridor (NEC) in the... A Connex commuter train stands by the platform in Melbourne, Australia Regional rail systems, or commuter rail systems, usually provide a rail service through a central business district area into suburbs or other locations that draw large numbers of people on a daily basis. ... MARC, prior to 1984 known as Maryland Rail Commuter Service, is a commuter rail system comprising three lines in the Baltimore-Washington Metropolitan Area. ... SEPTA redirects here. ... The New Jersey Transit Corporation (NJ Transit) is a statewide public transportation system serving the state of New Jersey, and Orange and Rockland counties in New York. ... Metro-North (officially MTA Metro-North Railroad) is a suburban commuter railroad running service from New York City to the northern suburbs in New York State and Connecticut. ...


The situation in Cleveland, Ohio is a little out of the ordinary. The light rail system uses overhead lines as expected. However, the heavy rail system also uses overhead lines instead of a third rail. Historically this is due to an ordinance intended to limit air pollution from the large number of trains passing through the city en route from New York to Chicago. Trains would switch locomotives at the Collinwood Rail Yardsabout 10 miles east or else reroute to the south of the city. Consequently, both light and heavy rail systems are able to share trackage for about three miles (5 km)along the red-line to Cleveland Hopkins Airport. Cleveland redirects here. ... Light rail vehicle on the Waterfront Line The Blue and Green Lines are the light rail component of the RTA Rapid Transit, a rail transit system in greater Cleveland, Ohio. ... The Red Line (Route 66X) is a rapid transit line of the RTA Rapid Transit in Cleveland, Ohio, running from Hopkins International Airport northeast to Tower City in downtown Cleveland, then east and northeast to Windermere. ... Third rail at the West Falls Church Metro stop in the Washington, D.C. area, electrified to 750 volts. ... Hopkins International Airport is an airport located approximately ten miles southwest of Cleveland, Ohio. ...


See also

Wikimedia Commons has media related to:
Overhead lines

  Results from FactBites:
 
Reference.com/Encyclopedia/Overhead lines (1802 words)
Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point.
Diesel trains may pass along these tracks without affecting the overhead line, although overhead clearance may be an issue.
On overhead wires designed for trolley poles this is done by having a neutral section between the wires, but this requires an insulator.
  More results at FactBites »

 
 

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