Pantograph (rail)
Overview
 
A pantograph for rail lines is a hinged electric-rod device that collects electric current from overhead lines
Overhead lines
Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point...

 for electric train
Train
A train is a connected series of vehicles for rail transport that move along a track to transport cargo or passengers from one place to another place. The track usually consists of two rails, but might also be a monorail or maglev guideway.Propulsion for the train is provided by a separate...

s or tram
Tram
A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...

s. The pantograph typically connects to a one-wire line, with the track acting as the ground wire. The term stems from the resemblance to pantograph lever-rod devices
Pantograph
A pantograph is a mechanical linkage connected in a special manner based on parallelograms so that the movement of one pen, in tracing an image, produces identical movements in a second pen...

 for copying handwriting and drawings.
A flat slide-pantograph was invented in 1895 at the Baltimore & Ohio Railroad and in Germany in 1900 by Siemens
Siemens
Siemens may refer toSiemens, a German family name carried by generations of telecommunications industrialists, including:* Werner von Siemens , inventor, founder of Siemens AG...

 & Halske.
The familiar diamond-shaped roller pantograph was invented by John Q.
Encyclopedia
A pantograph for rail lines is a hinged electric-rod device that collects electric current from overhead lines
Overhead lines
Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point...

 for electric train
Train
A train is a connected series of vehicles for rail transport that move along a track to transport cargo or passengers from one place to another place. The track usually consists of two rails, but might also be a monorail or maglev guideway.Propulsion for the train is provided by a separate...

s or tram
Tram
A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...

s. The pantograph typically connects to a one-wire line, with the track acting as the ground wire. The term stems from the resemblance to pantograph lever-rod devices
Pantograph
A pantograph is a mechanical linkage connected in a special manner based on parallelograms so that the movement of one pen, in tracing an image, produces identical movements in a second pen...

 for copying handwriting and drawings.

Invention

A flat slide-pantograph was invented in 1895 at the Baltimore & Ohio Railroad and in Germany in 1900 by Siemens
Siemens
Siemens may refer toSiemens, a German family name carried by generations of telecommunications industrialists, including:* Werner von Siemens , inventor, founder of Siemens AG...

 & Halske.
The familiar diamond-shaped roller pantograph was invented by John Q. Brown of the Key System
Key System
The Key System was a privately owned company which provided mass transit in the cities of Oakland, Berkeley, Alameda, Emeryville, Piedmont, San Leandro, Richmond, Albany and El Cerrito in the eastern San Francisco Bay Area from 1903 until 1960, when the system was sold to a newly formed public...

 shops for their commuter
Commuting
Commuting is regular travel between one's place of residence and place of work or full time study. It sometimes refers to any regular or often repeated traveling between locations when not work related.- History :...

 trains which ran between San Francisco
San Francisco, California
San Francisco , officially the City and County of San Francisco, is the financial, cultural, and transportation center of the San Francisco Bay Area, a region of 7.15 million people which includes San Jose and Oakland...

 and the East Bay
East Bay (San Francisco Bay Area)
The East Bay is a commonly used, informal term for the lands on the eastern side of the San Francisco Bay, in the San Francisco Bay Area, in California, United States...

 section of the San Francisco Bay Area
San Francisco Bay Area
The San Francisco Bay Area, commonly known as the Bay Area, is a populated region that surrounds the San Francisco and San Pablo estuaries in Northern California. The region encompasses metropolitan areas of San Francisco, Oakland, and San Jose, along with smaller urban and rural areas...

 in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

. They appear in photographs of the first day of service, 26 October 1903. For many decades thereafter, the same diamond shape was used by electric-rail systems around the world and remains in use by some today.

The pantograph was an improvement on the simple trolley pole
Trolley pole
A trolley pole is a tapered cylindrical pole of wood or metal, used to transfer electricity from a "live" overhead wire to the control and propulsion equipment of a tram or trolley bus. The use of overhead wire in a system of current collection is reputed to be the 1880 invention of Frank J....

, which prevailed up to that time, primarily because it allowed an electric-rail vehicle to travel at higher speeds without losing contact with the catenary
Overhead lines
Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point...

.

Modern use

of pantograph today is the so called half-pantograph (sometimes 'Z'-shaped), which has evolved to provide a more compact and responsive single-arm design at high speeds as trains get faster. The half-pantograph can be seen in use on everything from very fast trains (such as the TGV
TGV
The TGV is France's high-speed rail service, currently operated by SNCF Voyages, the long-distance rail branch of SNCF, the French national rail operator....

) to low-speed urban tram systems. The design operates with equal efficiency in either direction of motion, as demonstrated by the Swiss
SBB-CFF-FFS
Swiss Federal Railways and SFR are not in official use) is the national railway company of Switzerland headquartered in Bern. Formerly a government institution, it is since 1999 a special stock corporation with all shares held by the Swiss Confederation or the Swiss cantons...

 and Austrian
ÖBB
The Austrian Federal Railways is the national railway system of Austria, and the administrators of Liechtenstein's railways...

 railways whose newest high performance locomotives, the Re 460 and Taurus
EuroSprinter
The EuroSprinter family of electric locomotives is a modular concept of locomotives for the European market built by Siemens. The internal Siemens product name is ES 64, with ES for EuroSprinter and the number 64 indicating the 6,400 kW power at rail.Additional information is given in the name...

 respectively, operate with them set in opposite directions.

Technical details

for modern electric rail systems consists of an upper weight carrying wire (known as a catenary) from which is suspended a contact wire. The pantograph is spring-loaded and pushes a contact shoe up against the contact wire to draw the electricity needed to run the train. The steel rails on the tracks act as the electrical return
Ground (electricity)
In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....

. As the train moves, the contact shoe slides along the wire and can set up acoustical standing wave
Standing wave
In physics, a standing wave – also known as a stationary wave – is a wave that remains in a constant position.This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling...

s in the wires which break the contact and degrade current collection. This means that on some systems adjacent pantographs are not permitted.

Pantographs are the successor technology to trolley pole
Trolley pole
A trolley pole is a tapered cylindrical pole of wood or metal, used to transfer electricity from a "live" overhead wire to the control and propulsion equipment of a tram or trolley bus. The use of overhead wire in a system of current collection is reputed to be the 1880 invention of Frank J....

s, which were widely used on early streetcar systems. Trolley pole are still used by trolleybus
Trolleybus
A trolleybus is an electric bus that draws its electricity from overhead wires using spring-loaded trolley poles. Two wires and poles are required to complete the electrical circuit...

es, whose freedom of movement and need for a two-wire circuit makes pantographs impractical, and some streetcar networks, such as the Toronto Streetcar System
Toronto streetcar system
The Toronto streetcar system comprises eleven streetcar routes in Toronto, Ontario, Canada, operated by the Toronto Transit Commission , and is the largest such system in the Americas in terms of ridership, number of cars, and track length. The network is concentrated primarily in downtown and in...

, which have frequent turns sharp enough to require additional freedom of movement in their current collection to ensure unbroken contact.

Pantographs with overhead wires are now the dominant form of current collection for modern electric trains because, although more expensive and fragile than a third-rail
Third rail
A third rail is a method of providing electric power to a railway train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway track. It is used typically in a mass transit or rapid transit system, which has alignments in its own corridors, fully or almost...

 system, they allow the use of higher voltages.

Pantographs are typically operated by compressed air from the vehicle's braking system, either to raise the unit and hold it against the conductor or, when springs are used to effect the extension, to lower it. As a precaution against loss of pressure in the second case, the arm is held in the down position by a catch. For high-voltage systems, the same air supply is used to "blow out" the electric arc
Electric arc
An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...

 when roof-mounted circuit breakers are used.

Single- and double-arm pantographs

Pantographs may have either a single or a double arm. Double-arm pantographs are usually heavier, requiring more power to raise and lower, but may also be more fault-tolerant.

On railways of the former USSR, the most widely-used pantographs are those with a double arm ("made of two rhombs"), but since the late 1990s there have been some single-arm pantographs on Russian railways. Some streetcars use double-arm pantographs, among them the Russian KTM-5, KTM-8, LVS-86 and many other Russian-made trams, as well as some Euro-PCC trams in Belgium. American streetcars use either trolley pole
Trolley pole
A trolley pole is a tapered cylindrical pole of wood or metal, used to transfer electricity from a "live" overhead wire to the control and propulsion equipment of a tram or trolley bus. The use of overhead wire in a system of current collection is reputed to be the 1880 invention of Frank J....

s or single-arm pantographs.

Metro systems and overhead lines

Most rapid transit
Rapid transit
A rapid transit, underground, subway, elevated railway, metro or metropolitan railway system is an electric passenger railway in an urban area with a high capacity and frequency, and grade separation from other traffic. Rapid transit systems are typically located either in underground tunnels or on...

 systems are powered by a third rail
Third rail
A third rail is a method of providing electric power to a railway train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway track. It is used typically in a mass transit or rapid transit system, which has alignments in its own corridors, fully or almost...

, but some use pantographs, particularly ones that involve extensive above-ground running. Hybrid metro-tram or 'pre-metro' lines whose routes include tracks on city streets or in other publicly-accessible areas, such as the MBTA Green Line, must of course use overhead wire, since a third rail would normally present too great a risk of electrocution.

The only current exception to this is the new Bordeaux
Bordeaux
Bordeaux is a port city on the Garonne River in the Gironde department in southwestern France.The Bordeaux-Arcachon-Libourne metropolitan area, has a population of 1,010,000 and constitutes the sixth-largest urban area in France. It is the capital of the Aquitaine region, as well as the prefecture...

 tram system that uses an underground system called alimentation par sol
Ground-level power supply
Ground-level power supply, also known as surface current collection and Alimentation par Sol is a modern method of third-rail electrical pick-up for street trams. It was invented for the Bordeaux tramway, which was constructed from 2000 and opened in 2003. Until 2011, this is the only place it is...

, which only applies power to segments of track that are completely covered by the tram. This system is used in the historic centre of Bordeaux where an overhead wire system would cause a visual intrusion.

Overhead pantographs are sometimes used as alternatives to third rails because third rails can ice over in certain winter weather conditions. The MBTA Blue Line or the Wonderland Line
Wonderland (MBTA station)
Wonderland is the northern terminus of the Blue Line in the Massachusetts Bay Transportation Authority mass transit system serving greater Boston. The station is located near the site of the now-closed Wonderland Greyhound Park in Revere, Massachusetts, and is handicapped accessible. See MBTA...

 uses pantograph power for all of its surface route. The entire Metro systems of Barcelona
Barcelona Metro
The Barcelona Metro , part of the public transportation system of Barcelona, Catalonia, is an extensive network of electrified railways that run underground in central Barcelona and above ground into the city's suburbs. Since July 31, 2010, Barcelona Metro system consists of 11 lines with 165...

, Shanghai
Shanghai Metro
The Shanghai Metro is the urban rapid transit system of China's largest city, Shanghai. The system incorporates both subway and light rail lines. It opened in 1995, making Shanghai the third city in Mainland China, after Beijing and Tianjin, to have a rapid transit system...

, Hong Kong, and Seoul
Seoul Metropolitan Subway
The Seoul Metropolitan Subway or Metropolitan Subway in Seoul, in Seoul, South Korea, is one of the most heavily used rapid transit systems in the world, with well over 8 million trips daily on the system's thirteen lines...

 use overhead wiring and pantographs.

Until 2010 the Oslo
Oslo
Oslo is a municipality, as well as the capital and most populous city in Norway. As a municipality , it was established on 1 January 1838. Founded around 1048 by King Harald III of Norway, the city was largely destroyed by fire in 1624. The city was moved under the reign of Denmark–Norway's King...

 metro line 1 changed from third rail to overhead line power at Frøen station. Due to the many level crossings, it was deemed difficult to install a third rail on the rest of the older line 1 tracks.

See also

  • Bow collector
    Bow collector
    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. While once very common in continental Europe, it has now been largely replaced by the pantograph.-Origins:...

  • Contact shoe
    Current collector
    Electric current collectors are used for trolleybuses, trams, electric locomotives or EMUsto lead electrical power from overhead lines or electrical third rails to the electrical equipment of the vehicles....

  • Railway electrification system
    Railway electrification system
    A railway electrification system supplies electrical energy to railway locomotives and multiple units as well as trams so that they can operate without having an on-board prime mover. There are several different electrification systems in use throughout the world...

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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