Pantograph (transport)

Source: Wikipedia, the free encyclopedia.
For the duplication instrument, see Pantograph.
Schynige Platte railway in Schynige Platte
, built in 1911
Cross-arm pantograph of a Toshiba EMU

A pantograph (or "pan" or "panto") is an apparatus mounted on the roof of an electric train, tram or electric bus[1] to collect power through contact with an overhead line. The term stems from the resemblance of some styles to the mechanical pantographs used for copying handwriting and drawings.

The pantograph is a common type of current collector; typically, a single or double wire is used, with the return current running through the rails. Other types of current collectors include the bow collector and the trolley pole.

Invention

Early (1895) flat pantograph on a Baltimore & Ohio Railroad electric locomotive. The brass contact ran inside the Π section bar, so both lateral and vertical flexibility was necessary.

The pantograph, with a low-friction, replaceable graphite contact strip or "shoe" to minimise lateral stress on the contact wire, first appeared in the late 19th century. Early versions include the bow collector, invented in 1889 by Walter Reichel, chief engineer at Siemens & Halske in Germany,[2][3] and a flat slide-pantograph first used in 1895 by the Baltimore and Ohio Railroad[4]

The familiar diamond-shaped roller pantograph was devised and patented by John Q. Brown of the

East Bay section of the San Francisco Bay Area in California.[5][6][7][8] They appear in photographs of the first day of service, 26 October 1903.[9]
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, which prevailed up to that time, primarily because the pantograph allows an electric-rail vehicle to travel at much higher speeds without losing contact with the overhead lines, e.g. due to dewirement of the trolley pole.

Notwithstanding this, trolley pole current collection was used successfully at up to 140 km/h (90 mph) on the Electroliner vehicles of the Chicago North Shore and Milwaukee Railroad, also known as the North Shore Line.

Modern use

The most common type of pantograph today is the so-called half-pantograph (sometimes Z-shaped), which evolved to provide a more compact and responsive single-arm design at high speeds as trains got faster.

CENELEC, the European Committee for Electrotechnical Standardization.[11]

Technical details

Berlin Straßenbahn
. This pantograph uses a single-arm design.

The electric transmission system 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 underside of the contact wire to draw the current needed to run the train. The steel rails of the tracks act as the electrical return. As the train moves, the contact shoe slides along the wire and can set up standing waves
in the wires which break the contact and degrade current collection. This means that on some systems adjacent pantographs are not permitted.

Flexity Outlook LRV
with its pantograph raised. Note the trolley pole in the rear, which provides compatibility with sections not yet upgraded for pantograph operation.

Pantographs are the successor technology to trolley poles, which were widely used on early streetcar systems. Trolley poles are still used by trolleybuses, whose freedom of movement and need for a two-wire circuit makes pantographs impractical, and some streetcar networks, such as the Toronto streetcar system, which have frequent turns sharp enough to require additional freedom of movement in their current collection to ensure unbroken contact. However, many of these networks, including Toronto's, are undergoing upgrades to accommodate pantograph operation.

Pantographs with overhead wires are now the dominant form of current collection for modern electric trains because, although more fragile than a third rail 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 when roof-mounted circuit breakers are used.[12][13]

Single and double pantographs

Close-up view of a Brecknell Willis pantograph on a British Rail Class 333
Diagram of parts of a pantograph from ICE S
Class 85
locomotive, used on early AC electric locomotives from the 1960s

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 poles
or single-arm pantographs.

A Pantograph of a CAF tram in Belgrade

Metro systems and overhead lines

Symmetrical, diamond-shaped pantographs on a Prague tram

Most rapid transit systems are powered by a third rail, but some use pantographs, particularly ones that involve extensive above-ground running. Most hybrid metro-tram or 'pre-metro' lines whose routes include tracks on city streets or in other publicly accessible areas, such as (formerly) line 51 of the Amsterdam Metro, the MBTA Green Line, RTA Rapid Transit in Cleveland, Frankfurt am Main U-Bahn, and San Francisco's Muni Metro, use overhead wire, as a standard third rail would obstruct street traffic and present too great a risk of electrocution.

Among the various exceptions are several tram systems, such as the ones in

AnsaldoBreda, CAF, and others. These may consist of physical ground-level infrastructure, or use energy stored in battery packs
to travel over short distances without overhead wiring.

Overhead pantographs are sometimes used as alternatives to third rails because third rails can ice over in certain winter weather conditions. The

Osaka, Nagoya, Singapore, Sapporo, Budapest, and Mexico City). Pantographs were also used on the Nord-Sud Company rapid transit lines in Paris until the other operating company of the time, Compagnie du chemin de fer métropolitain de Paris
, bought out the company and replaced all overhead wiring with the standard third rail system used on other lines.

Numerous railway lines use both third rail and overhead power collection along different portions of their routes, generally for historical reasons. They include the

Crawford-East Prairie station
. Here, trains bound for Dempster-Skokie would raise their pantographs, while those bound for Howard would lower theirs, doing so at speed in both instances. In 2005, due to the cost and unique maintenance needs for what only represented a very small portion of the system, the overhead system was removed and replaced with the same third rail power that was used throughout the rest of the system, which allowed all of Chicago's railcars to operate on the line. All the pantographs were removed from the Skokie equipped cars.

Until 2010, the

single track.[15]
After 2010 third rails were used in spite of level crossings. The third rails have gaps, but there are two contact shoes.

Three-phase supply

Experimental three-phase railcar, Germany, 1901

On some systems using three phase power supply, locomotives and power cars have two pantographs with the third-phase circuit provided by the running rails. In 1901 an experimental high-speed installation, another design from Walter Reichel at Siemens & Halske, used three vertically mounted overhead wires with the collectors mounted on horizontally extending pantographs.[16][17]

Inclined pantographs

Tilted pantograph used with offset overhead line to allow loading of open wagons

On lines where open wagons are loaded from above, the overhead line may be offset to allow this; the pantographs are then mounted at an angle to the vertical.[18]

Weaknesses

Contact between a pantograph and an overhead line is usually assured through a block of graphite. This material conducts electricity while working as a lubricant. As graphite is brittle, pieces can break off during operation. Bad pantographs can seize the overhead wire and tear it down, so there is a two-way influence whereby bad wires can damage the pantograph and bad pantographs can damage the wires. To prevent this, a pantograph monitoring station can be used. At sustained high speeds, above 300 km/h (190 mph), friction can cause the contact strip to become red hot, which in turn can cause excessive arcing and eventual failure.[19]

In the UK, the pantographs (

Stone Faiveley) of vehicles are raised by air pressure and the graphite contact "carbons" create an air gallery in the pantograph head which release the air if a graphite strip is lost, activating the automatic drop device and lowering the pantograph to prevent damage. Newer electric traction units may use more sophisticated methods which detect the disturbances caused by arcing at the point of contact when the graphite strips are damaged. There are not always two pantographs on an electric multiple unit but, in cases where there are, the other one can be used if one is damaged; an example of this situation would be a Class 390 Pendolino
. The rear pantograph in relation to the direction of travel is often used as to avoid damaging both pantographs in case of entanglements: if the front pantograph was used, debris from an entanglement could cause damage to the rear pantograph, rendering both pantographs and the vehicle inoperable.

Automatic dropping device

Automatic dropping device (ADD) is a safety device that automatically lowers the pantograph on electric trains to prevent accidents in case of obstructions or emergencies.[20][21] It is also known as pantograph dropping device.[22] The automatic dropping device is obligatory for trains with operational speeds of 160 km/h and higher. Otherwise, the train operators are free to install these devices. The damage that causes the pantograph to fall can include the strip head, the pantograph head and other parts. The ADD mostly uses a pneumatic system to detect a damage. For example, a broken contact strip will cause a pressure drop in the air tube inside.

See also

References

Wikimedia Commons has media related to Pantograph.
  1. ^ "Solaris Urbino". Busworld. 4 September 2016.
  2. ^ "A Century of Traction. Electrical Inspections, page 7, by Basil Silcove". Archived from the original on 2015-04-02.
  3. ^ Italian Patent 35389/285, 18 December 1893; US patent 547031, 1 October 1895
  4. ^ "A ninety-six ton electric locomotive". Scientific American. New York. 10 August 1895.
  5. ^ US Patent No. 764,224
  6. ^ The Street Railway Journal, Vol.24, No.3, July 16, 1904, p.116
  7. ^ The Key Route, Harre Demoro, v.1, pp.16-17, publ. Interurban Press (1985)
  8. ^ Sappers, Vernon (2007). Key System Streetcars. Signature Press. p. 369.
  9. ^ Walter Rice and Emiliano Echeverria (2007). The Key System: San Francisco and the Eastshore Empire. Arcadia Publishing. pp. 13, 16.
  10. ^ Louis Faiveley, Current Collecting Device, US 2935576 , granted May 3, 1960.
  11. ^ "Railway applications - Current collection systems - Technical criteria for the interaction between pantograph and overhead contactline (to achieve free access)" (PDF). National Standards Authority of Ireland. Retrieved 27 March 2020.
  12. OCLC 467723
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  13. OCLC 2683266
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  14. ^ Garfield, Graham. "Yellow Line". Chicago "L".org. Retrieved January 8, 2011.
  15. ^ exsuhmsgate2 (5 March 2010). "Oslo Metro in transition III: Frognerseteren line". Archived from the original on 2021-11-17 – via YouTube.{{cite web}}: CS1 maint: numeric names: authors list (link)
  16. ISBN 9783835631328
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  17. ^ "Walter Reichel". siemens.com. Retrieved 27 March 2020.
  18. ISSN 1234-5962
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  19. ISBN 0275973778
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  20. ^ Xin, Tingyu (1 July 2019). Non-invasive dynamic condition assessment techniques for railway pantographs. University of Birmingham.
  21. ^ "IEC 60494-1:2013 - IEC-Normen - VDE VERLAG". www.vde-verlag.de. Retrieved 3 August 2023.
  22. ^ "IEC 60050 - International Electrotechnical Vocabulary - Details for IEV number 811-32-22: "pantograph dropping device"". www.electropedia.org. Retrieved 9 August 2023.
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