Overhead line

This article is about the transmission of electrical power to road and rail vehicles. For transmission of bulk electrical power to general consumers, seeElectric power transmission.For powerlines mounted on pylons, seeOverhead power line.For lines carrying information, seeOverhead cable.

Anoverhead lineoroverhead wireis anelectrical cablethat is used to transmitelectrical energytoelectric locomotives,electric multiple units,trolleybusesortrams.The generic term used by theInternational Union of Railwaysfor the technology isoverhead line.It is known variously asoverhead catenary,overhead contact line(OCL),overhead contact system(OCS),overhead equipment(OHE),overhead line equipment(OLEorOHLE),overhead lines(OHL),overhead wiring(OHW),traction wire,andtrolley wire.

Overhead lines

An overhead line consists of one or morewires(orrails,particularly in tunnels) situated overrail tracks,raised to a high electrical potential by connection to feeder stations at regularly spaced intervals along the track. The feeder stations are usually fed from ahigh-voltageelectrical grid.

Overview

Electric trains that collect their current from overhead lines use a device such as apantograph,bow collectorortrolley pole.It presses against the underside of the lowest overhead wire, the contact wire. Current collectors are electrically conductive and allow current to flow through to the train or tram and back to the feeder station through the steel wheels on one or both running rails. Non-electriclocomotives(such asdiesels) may pass along these tracks without affecting the overhead line, although there may be difficulties withoverhead clearance.Alternative electrical power transmission schemes for trains includethird rail,ground-level power supply,batteriesandelectromagnetic induction.

Vehicles like buses that have rubber tyres cannot provide a return path for the current through their wheels, and must instead use a pair of overhead wires to provide both the current and its return path.

Construction

Lineworkerson amaintenance of wayvehicle repairing overhead lines (Poland)

Overhead over a switch inToronto:Two runners for pantographs flank the trolley pole frog.

To achieve good high-speed current collection, it is necessary to keep the contact wire geometry within defined limits. This is usually achieved by supporting the contact wire from a second wire known as themessenger wireorcatenary.This wire approximates the natural path of a wire strung between two points, acatenary 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". It is supported regularly at structures, by apulley,link orclamp.The whole system is then subjected to mechanicaltension.

As the pantograph moves along under the contact wire, the carbon insert on top of the pantograph becomes worn with time. On straight track, the contact wire iszigzaggedslightly to the left and right of the centre from each support to the next so that the insert wears evenly, thus preventing any notches. On curves, the "straight" wire between the supports causes the contact point to cross over the surface of the pantograph as the train travels around the curve. The movement of the contact wire across the head of the pantograph is called the "sweep".

The zigzagging of the overhead line is not required for trolley poles. Fortramways,a contact wire without a messenger wire is used.

Depot areas tend to have only a single wire and are known as "simple equipment" or "trolley wire". When overhead line systems were first conceived, good current collection was possible only at low speeds, using a single wire. To enable higher speeds, two additional types of equipment were developed:

• Stitched equipment uses an additional wire at each support structure, terminated on either side of the messenger/catenary wire.
• Compound equipment uses a second support wire, known as the "auxiliary", between the messenger/catenary wire and the contact wire. Droppers support the auxiliary from the messenger wire, while additional droppers support the contact wire from the auxiliary. The auxiliary wire can be of a more conductive but less wear-resistant metal, increasing transmission efficiency.

Earlier dropper wires provided physical support of the contact wire without joining the catenary and contact wires electrically. Modern systems use current-carrying droppers, eliminating the need for separate wires.

The present transmission system originated about 100 years ago. A simpler system was proposed in the 1970s by the Pirelli Construction Company, consisting of a single wire embedded at each support for 2.5 metres (8 ft 2 in) of its length in a clipped, extruded aluminum beam with the wire contact face exposed. A somewhat higher tension than used before clipping the beam yielded a deflected profile for the wire that could be easily handled at 400 km/h (250 mph) by a pneumatic servo pantograph with only 3gacceleration.

Parallel overhead lines

A switch in parallel overhead lines

Trolleybus wire switch

An electrical circuit requires at least two conductors. Trams and railways use the overhead line as one side of the circuit and the steel rails as the other side of the circuit. For atrolleybusor atrolleytruck,norailsare available for the return current, as the vehicles use rubber tyres on the road surface. Trolleybuses use a second parallel overhead line for the return, and twotrolley poles,one contacting each overhead wire. (Pantographsare generally incompatible with parallel overhead lines.) The circuit is completed by using both wires. Parallel overhead wires are also used on the rare railways withthree-phase AC railway electrification.

Types of wires

In theSoviet Unionthe following types of wires/cables were used.For the contact wire, cold drawn solid copper was used to ensure goodconductivity.The wire is not round but has grooves at the sides to allow the hangers to attach to it. Sizes were (in cross-sectional area) 85, 100, or 150 mm².To make the wire stronger, 0.04% tin might be added. The wire must resist the heat generated by arcing and thus such wires should never be spliced by thermal means.

The messenger (or catenary) wire needs to be both strong and have good conductivity. They used multi-strand wires (or cables) with 19 strands in each cable (or wire). Copper, aluminum, and/or steel were used for the strands. All 19 strands could be made of the same metal or a mix of metals based on the required properties. For example, steel wires were used for strength, while aluminium or copper wires were used for conductivity.Another type looked like it had all copper wires but inside each wire was a steel core for strength. The steel strands were galvanized but for better corrosion protection they could be coated with an anti-corrosion substance.

InSlovenia,where 3 kV system is in use, standard sizes for contact wire are 100 and 150 mm².The catenary wire is made of copper or copper alloys of 70, 120 or 150 mm².The smaller cross sections are made of 19 strands, whereas the bigger has 37 strands. Two standard configurations for main lines consist of two contact wires of 100 mm²and one or two catenary wires of 120 mm²,totaling 320 or 440 mm².Only one contact wire is often used for side tracks.

In theUKandEU countries,the contact wire is typically made from copper alloyed with other metals. Sizes include cross-sectional areas of 80, 100, 107, 120, and 150 mm².Common materials include normal and high strength copper, copper-silver, copper-cadmium, copper-magnesium, and copper-tin, with each being identifiable by distinct identification grooves along the upper lobe of the contact wire. These grooves vary in number and location on the arc of the upper section.Copper is chosen for its excellent conductivity, with other metals added to increase tensile strength. The choice of material is chosen based on the needs of the particular system, balancing the need for conductivity and tensile strength.

Tensioning

Line tensioning in Germany

Catenary wires are kept in mechanical tension because the pantograph causes mechanicaloscillationsin the wire. Thewavesmust travel faster than the train to avoid producingstanding waves,which could break the wire. Tensioning the line makes waves travel faster, and also reduces sag from gravity.

For medium and high speeds, the wires are generally tensioned by weights or occasionally by hydraulic tensioners. Either method is known as "auto-tensioning" (AT) or "constant tension" and ensures that the tension is virtually independent of temperature. Tensions are typically between 9 and 20kN(2,000 and 4,500lbf) per wire. Where weights are used, they slide up and down on a rod or tube attached to the mast, to prevent them from swaying. Recently, spring tensioners have started to be used. These devices contain a torsional spring with a cam arrangement to ensure a constant applied tension (instead of varying proportionally with extension). Some devices also include mechanisms for adjusting the stiffness of the spring for ease of maintenance.

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. The tension is generally about 10 kN (2,200 lbf). This type of equipment sags in hot conditions and is taut in cold conditions.

With AT, the continuous length of the overhead line is limited due to the change in the height of the weights as the overhead line expands and contracts with temperature changes. This movement is proportional to the distance between anchors. Tension length has a maximum. For most25 kVOHL equipment in the UK, the maximum tension length is 1,970 m (6,460 ft).

An additional issue with AT equipment is that, if balance weights are attached to both ends, the whole tension length is free to move along the track. To avoid this a midpoint anchor (MPA), close to the centre of the tension length, restricts movement of the messenger/catenary wire by anchoring it; the contact wire and its suspension hangers can move only within the constraints of the MPA. MPAs are sometimes fixed to low bridges, or otherwise anchored to vertical catenary poles or portal catenary supports. A tension length can be seen as a fixed centre point, with the two half-tension lengths expanding and contracting with temperature.

Most systems include a brake to stop the wires from unravelling completely if a wire breaks or tension is lost. German systems usually use a single large tensioning pulley (basically aratchetmechanism) with a toothed rim, mounted on an arm hinged to the mast. Normally the downward pull of the weights and the reactive upward pull of the tensioned wires lift the pulley so its teeth are well clear of a stop on the mast. The pulley can turn freely while the weights move up or down as the wires contract or expand. If tension is lost the pulley falls back toward the mast, and one of its teeth jams against the stop. This stops further rotation, limits the damage, and keeps the undamaged part of the wire intact until it can be repaired. Other systems use various braking mechanisms, usually with multiple smaller pulleys in ablock and tacklearrangement.

Breaks

Lines are divided into sections to limit the scope of an outage and to allow maintenance.

Section break

A section insulator at a section break in Amtrak's 12 kV catenary

To allow maintenance to the overhead line without having to turn off the entire system, the line is broken into electrically separated portions known as "sections". Sections often correspond with tension lengths. The transition from section to section is known as a "section break" and is set up so that the vehicle's pantograph is in continuous contact with one wire or the other.

For bow collectors and pantographs, this is done by having two contact wires run side by side over the length between 2 or 4 wire supports. A new one drops down and the old one rises up, allowing the pantograph to smoothly transfer from one to the other. The two wires do not touch (although the bow collector or pantograph is briefly in contact with both wires). In normal service, the two sections are electrically connected; depending on the system this might be an isolator, fixed contact or a Booster Transformer. The isolator allows the current to the section to be interrupted for maintenance.

On overhead wires designed for trolley poles, this is done by having a neutral section between the wires, requiring an insulator. The driver of thetramortrolleybusmust temporarily reduce the power draw before the trolley pole passes through, to prevent arc damage to the insulator.

Pantograph-equipped locomotives must not run through a section break when one side is de-energized. The locomotive would become trapped, but as it passes the section break the pantograph briefly shorts the two catenary lines. If the opposite line is de-energized, this voltage transient may trip supply breakers. If the line is under maintenance, an injury may occur as the catenary is suddenly energized. Even if the catenary is properly grounded to protect the personnel, thearcgenerated across the pantograph can damage the pantograph, the catenary insulator or both.

Neutral section (phase break)

Neutral Section Indication Board used on railways in theUK.Six of these would be required atcrossings

Apantographof EMU passes neutral section of25 kV 50 Hz AC overhead linewithout lowering but with switching off a circuit breaker

Sometimes on a larger electrified railway, tramway or trolleybus system, it is necessary to power different areas of track from different power grids, without guaranteeing synchronisation of the phases. Long lines may be connected to the country's national grid at various points and different phases. (Sometimes the sections are powered with different voltages or frequencies.) The grids may be synchronised on a normal basis, but events may interrupt synchronisation. This is not a problem forDCsystems.ACsystems have a particular safety implication in that the railway electrification system would act as a "Backdoor" connection between different parts, resulting in, amongst other things, a section of the grid de-energised for maintenance being re-energised from the railway substation creating danger.

For these reasons, Neutral sections are placed in the electrification between the sections fed from different points in a national grid, or different phases, or grids that are not synchronized. It is highly undesirable to connect unsynchronized grids. A simple section break is insufficient to guard against this as the pantograph briefly connects both sections.

In countries such as France, South Africa, Australia and the United Kingdom, a pair of permanent magnets beside the rails at either side of the neutral section operate a bogie-mountedtransduceron the train which causes a large electrical circuit-breaker to open and close when the locomotive or the pantograph vehicle of a multiple unit passes over them.In the United Kingdom equipment similar toAutomatic Warning System(AWS) is used, but with pairs of magnets placedoutsidethe running rails (as opposed to the AWS magnets placed midway between the rails). Lineside signs on the approach to the neutral section warn the driver to shut off traction power and coast through the dead section.

A neutral section or phase break consists of two insulated breaks back-to-back with a short section of line that belongs to neither grid. Some systems increase the level of safety by the midpoint of the neutral section being earthed. The presence of the earthed section in the middle is to ensure that should the transducer controlled apparatus fail, and the driver also fail to shut off power, the energy in the arc struck by the pantograph as it passes to the neutral section is conducted to earth, operating substation circuit breakers, rather than the arc either bridging the insulators into a section made dead for maintenance, a section fed from a different phase, or setting up a Backdoor connection between different parts of the country's national grid.

25 kV AC neutral zone in Romania

On thePennsylvania Railroad,phase breaks were indicated by a position light signal face with all eight radial positions with lenses and no center light. When the phase break was active (the catenary sections out of phase), all lights were lit. The position light signal aspect was originally devised by the Pennsylvania Railroad and was continued byAmtrakand adopted byMetro North.Metal signs were hung from the catenary supports with the letters "PB" created by a pattern of drilled holes.

Dead section

A special category of phase break was developed in America, primarily by the Pennsylvania Railroad. Since its traction power network was centrally supplied and only segmented by abnormal conditions, normal phase breaks were generally not active. Phase breaks that were always activated were known as "Dead Sections": they were often used to separate power systems (for example, the Hell's Gate Bridge boundary between Amtrak andMetro North's electrifications) that would never be in-phase. Since a dead section is always dead, no special signal aspect was developed to warn drivers of its presence, and a metal sign with "DS" in drilled-hole letters was hung from the catenary supports.

Gaps

Aswing bridgenearMeppel,the Netherlands. There is no overhead line on the bridge; the train coasts through with raised pantograph.

Occasionally gaps may be present in the overhead lines, when switching from one voltage to another or to provide clearance for ships at moveable bridges, as a simpler alternative for moveable overhead power rails. Electric trains coast across the gaps. To prevent arcing, power must be switched off before reaching the gap and usually the pantograph would be lowered.

Overhead conductor rails

B&O's overhead third-rail system atGuilford Avenuein Baltimore, 1901, part of theBaltimore Belt Line.The central position of the overhead conductors was dictated by the many tunnels on the line: the∩-shaped rails were located at the highest point in the roof to give the most clearance.

Given limitedclearancesuch as intunnels,the overhead wire may be replaced by a rigid overhead rail. An early example was in the tunnels of theBaltimore Belt Line,where aΠsection bar (fabricated from three strips of iron and mounted on wood) was used, with the brass contact running inside the groove.When the overhead line was raised in theSimplon Tunnelto accommodate taller rolling stock, a rail was used. A rigid overhead rail may also be used in places where tensioning the wires is impractical, for example onmoveable bridges.In modern uses, it is very common for underground sections of trams, metros, and mainline railways to use a rigid overhead wire in their tunnels, while using normal overhead wires in their above ground sections.

Operation of the overhead conductor rails at Shaw's Cove Railroad Bridge in Connecticut

In a movable bridge that uses a rigid overhead rail, there is a need to transition from the catenary wire system into an overhead conductor rail at the bridge portal (the lasttraction current pylonbefore the movable bridge). For example, the power supply can be done through a catenary wire system near aswing bridge.The catenary wire typically comprises messenger wire (also called catenary wire) and a contact wire where it meets the pantograph. The messenger wire is terminated at the portal, while the contact wire runs into the overhead conductor rail profile at the transition end section before it is terminated at the portal. There is a gap between the overhead conductor rail at the transition end section and the overhead conductor rail that runs across the entire span of the swing bridge. The gap is required for the swing bridge to be opened and closed. To connect the conductor rails together when the bridge is closed, there is another conductor rail section called "rotary overlap" that is equipped with a motor. When the bridge is fully closed, the motor of the rotary overlap is operated to turn it from a tilted position into the horizontal position, connecting the conductor rails at the transition end section and the bridge together to supply power.

Short overhead conductor rails are installed attram stopsas for theCombino Supra.

Crossings

Tram overhead wire (diagonal) crossing trolleybus wires (horizontal), photographed in Bahnhofplatz, Bern, Switzerland

Annotated version of the previous photo, highlighting components

tram conductor

trolley bus wires

insulated trough

Tramsdraw their power from a single overhead wire at about 500 to 750VDC.Trolleybusesdraw from two overhead wires at a similar voltage, and at least one of the trolleybus wires must be insulated from tram wires. This is usually done by the trolleybus wires running continuously through the crossing, with the tramconductorsa few centimetres lower. Close to the junction on each side, the tram wire turns into a solid bar running parallel to the trolleybus wires for about half a metre. Another bar similarly angled at its ends is hung between the trolleybus wires, electrically connected above to the tram wire. The tram's pantograph bridges the gap between the different conductors, providing it with a continuous pickup.

Where the tram wire crosses, the trolleybus wires are protected by an inverted trough ofinsulatingmaterial extending 20 or 30 mm (0.79 or 1.18 in) below.

Until 1946, a level crossing inStockholm,Swedenconnected therailwaysouth of Stockholm Central Station and a tramway. The tramway operated on 600–700 V DC and the railway on15 kV AC.In the Swiss village ofOberentfelden,theMenziken–Aarau–Schöftland lineoperating at 750 V DC crosses theSBBline at 15 kV AC; there used to be a similar crossing between the two lines atSuhrbut this was replaced by an underpass in 2010. Some crossings between tramway/light rail and railways are extant in Germany. InZürich,Switzerland,VBZtrolleybusline 32 has a level crossing with the 1,200 VDCUetliberg railway line;at many places, trolleybus lines cross the tramway. In some cities, trolleybuses and trams shared a positive (feed) wire. In such cases, a normal trolleybus frog can be used.

Alternatively, section breaks can be sited at the crossing point, so that the crossing is electrically dead.

Australia

Many cities had trams and trolleybuses using trolley poles. 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.

InMelbourne,Victoria, tram drivers put the controller into neutral and coast through section insulators, indicated by insulator markings between the rails.

Melbourne has several remaininglevel crossingsbetween electrified suburban railways and tram lines. They have mechanical switching arrangements (changeover switch) to switch the 1500 V DC overhead of the railway and the 650 V DC of the trams, called a Tram Square.Several such crossings have been grade separated in recent years as part of theLevel Crossing Removal Project.

Greece

Athenshas two crossings oftramand trolleybus wires, at Vas. Amalias Avenue and Vas. Olgas Avenue, and at Ardittou Street and Athanasiou Diakou Street. They use the above-mentioned solution.

Italy

InRome,at the crossing between Viale Regina Margherita and Via Nomentana, tram and trolleybus lines cross: tram on Viale Regina Margherita and trolleybus on Via Nomentana. The crossing is orthogonal, therefore the typical arrangement was not available.

InMilan,mosttram linescrossits circular trolleybus lineonce or twice. Trolleybus and tram wires run parallel in streets such as viale Stelvio, viale Umbria and viale Tibaldi.

Multiple overhead lines

Twooverhead conductor railsfor the same track. Left, 1,200 V DC for theUetliberg railway(the pantograph is mounted asymmetrically to collect current from this rail); right, 15 kV AC for the Sihltal railway

Some railways used two or three overhead lines, usually to carrythree-phasecurrent. This is used only on theGornergrat RailwayandJungfrau Railwayin Switzerland, thePetit train de la Rhunein France, and theCorcovado Rack Railwayin Brazil. Until 1976, it was widely used in Italy. On these railways, the two conductors 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.

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 (1.1 mi)), the military railway between Marienfelde and Zossen between 1901 and 1904 (length 23.4 kilometres (14.5 mi)) and an 800-metre (2,600 ft)-long section of a coal railway near Cologne between 1940 and 1949.

On DC systems, bipolar overhead lines were sometimes used to avoidgalvanic corrosionof metallic parts near the railway, such as on theChemin de fer de la Mure.

All systems with multiple overhead lines have a 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.

TheSihltal Zürich Uetliberg Bahnhad two lines with different electrification. To be able to use different electric systems on shared tracks, theSihltal linehad its overhead wire right above the train, whilst theUetliberg linehad its overhead wire off to one side. This configuration was used up until summer 2022, since then theUetliberg linehas been switched to the standard 15kV 16.7 Hz configuration.

Overhead catenary

Catenary (upper photo) is suited to higher-speed rail vehicles. Trolley wire (lower photo) is suited to slower-speed trams (streetcars) and light rail vehicles.

Overhead feeding rail on theRERLine Ctrenches and tunnels in central Paris

Compound catenary equipment ofJR West

An older rail bridge inBerwick-upon-Tweed,retrofitted to include overhead catenary lines

A catenary is a system of overheadwiresused to supplyelectricityto alocomotive,tram(streetcar), orlight railvehicle that is equipped with apantograph.

Gantry with old and new suspended equipment atGrivita railway station,Bucharest

Unlike simple overhead wires, in which the uninsulated wire is attached by clamps to closely spaced crosswires supported by poles, catenary systems use at least two wires. The catenary or messenger wire is hung at a specific tension between line structures, and a second wire is held intensionby the messenger wire, attached to it at frequent intervals byclampsand connecting wires known asdroppers.The second wire is straight and level, parallel to therail track,suspended over it as the roadway of asuspension bridgeis over water.

Catenary systems are suited to high-speed operations whereas simple wire systems, which are less expensive to build and maintain, are common on light rail or tram (streetcar) lines, especially on city streets. Such vehicles can be fitted with either a pantograph ortrolley pole.

Overhead catenary systems in the United States

TheNortheast Corridorin theUnited Stateshas catenary over the 600 miles (970 km) betweenBoston,MassachusettsandWashington, D.C.,forAmtrak'sinter-citytrains.Commuter railagencies includingMARC,SEPTA,NJ Transit,andMetro-North Railroadutilize the catenary to provide local service.

InCleveland, Ohio,theinterurban/light raillines and theheavy railline use the same overhead wires, due to a city ordinance intended to limit air pollution from the large number of steam trains that passed through Cleveland between the east coast and Chicago. Trains switched from steam to electric locomotives at the Collinwood railyards about 10 miles (16 km) east of Downtown and atLinndaleon the west side. When Cleveland constructed its rapid transit (heavy rail) line between the airport, downtown, and beyond, it employed a similar catenary, using electrification equipment left over after railroads switched from steam to diesel. Light and heavy rail share trackage for about 3 miles (4.8 km) along theCleveland Hopkins International AirportRed (heavy rail) line,Blue and Green interurban/light rail linesbetweenCleveland Union Terminaland just past East 55th Street station, where the lines separate.

Part ofBoston'sBlue Linethrough the northeast suburbs uses overhead lines, as does the Green Line.

TheYellow Lineon theChicago "L"used an overhead catenary system for the west half of the route, transitioning to third rail for the east half. This was discontinued in 2004 when the entire route was converted to third rail.

On theSan Francisco peninsulainCalifornia,theCaltraincommuter railsystem completed the installation of an overhead contact system (OCS) in 2023, to prepare for the conversion of its 160-year oldSan FranciscotoSan JoséPeninsula Corridor to fully-electrified revenue service in September 2024.

Height

The height of the overhead line can create hazards atlevel crossings,where it may be struck by road vehicles. Warning signs are placed on the approaches, advising drivers of the maximum safe height.

The wiring in most countries is too low to allowdouble stack containertrains. TheChannel Tunnelhas an extended height overhead line to accommodate double-height car and truck transporters.ChinaandIndiaoperate lines electrified with extra height wiring and pantographs to allow for double stack container trains.

Problems with overhead equipment

Overhead lines may be adversely affected by strong winds causing wires to swing.Power storms can knock the power out withlightningstrikes on systemswith overhead wires, stopping trains following apower surge.

During cold or frosty weather, ice may coat overhead lines. This can result in poor electrical contact between the collector and the overhead line, resulting in electrical arcing and power surges.Ice coatings also add extra weight, as well as increase their surface area exposed to wind, consequently increasing the load on the wires and their supports.

Lines may sag during hot weather and if a pantograph gets entangled, this can result in a dewirement. Similarly, in very cold weather they may contract and snap.

The installation of overhead lines may require reconstruction of bridges to provide safe electrical clearance.

Overhead lines, like most electrified systems, require a greatercapital expenditurewhen building the system than an equivalent non-electric system. While a unelectrified railway line requires only the grade, ballast, ties and rails, an overhead system also requires a complex system of support structures, lines, insulators, power-control systems and power lines, all of which require maintenance. This makes non-electrical systems more attractive in the short term, although electrical systems can pay for themselves eventually. Also, the added construction and maintenance cost-per-mile makes overhead systems less attractive on already existing long-distance railways, such as those found in North America, where the distances between cities are typically far greater than in Europe. Such long lines require enormous investment in overhead line equipment, which private rail companies are unlikely to be interested in, and major difficulties confront energizing long portions of overhead wire on a permanent basis, especially in areas where energy demand already outstrips supply.

Many people consider overhead lines to be "visual pollution",due to the many support structures and complicated system of wires and cables that fill the air. Such considerations have driven the move towards replacing overhead power and communications lines with buried cables where possible. The issue came to a head in the UK with theGreat Western Main Lineelectrification scheme, especially through theGoring Gap.A protest group with their own website has been formed.

The valuable copper conductor can also be subject to theft, as for example theLahore-Khanewal line in Pakistanand theGweru-Harare section of line in Zimbabwe.

History

The first tram with overhead lines was presented byWerner von Siemensat the1881 International Exposition of ElectricityinParis:the installation was removed after that event. In October 1883, the first permanent tram service with overhead lines was on theMödling and Hinterbrühl Tramin Austria. The trams had bipolar overhead lines, consisting of two U-pipes, in which the pantographs hung and ran like shuttles. From April to June 1882, Siemens had tested a similar system on hisElectromote,an early precursor of thetrolleybus.

Much simpler and more functional was an overhead wire in combination with a pantograph borne by the vehicle and pressed at the line from below. This system, for rail traffic with a unipolar line, was invented byFrank J. Spraguein 1888. From 1889 it was used at theRichmond Union Passenger RailwayinRichmond, Virginia,pioneering electric traction.

See also

• Catenary maintenance vehicle
• Electro-diesel locomotive
• Gantry
• Insulator (electricity)
• Lineworker
• List of railway electrification systems
• Railway electrification
• Traction current pylon
• Utility pole

Further reading

• Cooper, B.K. (February–March 1982). "Catenaries and Contact Wires".Rail Enthusiast.EMAP National Publications. pp. 14–16.ISSN0262-561X.OCLC49957965.
• "Garry Keenor – Overhead Line Electrification for Railways".Retrieved2019-02-05.
• "Trans Power Guide".Archived fromthe originalon 2020-07-16.Retrieved2019-03-06.
• Liudvinavičius, Lionginas; Dailydka, Stasys (1 January 2016)."The Aspects of Catenary Maintenance of Direct Current (DC) and Alternating Current (AC)".Procedia Engineering.134:268–275.doi:10.1016/j.proeng.2016.01.007.ISSN1877-7058.

External links

• "[IRFCA] Indian Railways FAQ: Electric Traction - I".irfca.org.Retrieved2018-03-06.