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 19thcentury. 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 Key System shops for their commuter trains which ran between San Francisco and 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 140km/h (90mph) 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. Louis Faiveley invented this type of pantograph in 1955.[10] The half-pantograph can be seen in use on everything from very fast trains (such as the TGV) to low-speed urban tram systems. The design operates with equal efficiency in either direction of motion, as demonstrated by the Swiss and Austrian railways whose newest high-performance locomotives, the Re 460 and Taurus, operate with them set in the opposite direction. In Europe the geometry and shape of the pantographs are specified by CENELEC, the European Committee for Electrotechnical Standardization.[11]
Technical details
The (asymmetrical) Z-shaped pantograph of the electrical pickup on the 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.
A 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 333Diagram of parts of a pantograph from ICE SFirst-generation Faiveley single-arm pantograph on a British Rail 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.
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 Bordeaux, Angers, Reims and Dubai that use a proprietary underground system developed by Alstom, called APS, which only applies power to segments of track that are completely covered by the tram. This system was originally designed to be used in the historic centre of Bordeaux because an overhead wire system would cause a visual intrusion. Similar systems that avoid overhead lines have been developed by Bombardier, 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.
Numerous railway lines use both third rail and overhead power collection along different portions of their routes, generally for historical reasons. They include the North London line and West London lines of London Overground, the Northern City Line of Great Northern, three of the five lines in the Rotterdam Metro network, Metro-North Railroad'sNew Haven Line, and the Chicago Transit Authority's Yellow Line. In this last case, the overhead portion was a remnant of the Chicago North Shore and Milwaukee Railroad's high-speed Skokie Valley Route,[14] and was the only line on the entire Chicago subway system to utilize pantograph collection for any length. As such, the line required railcars that featured pantographs as well as third rail shoes, and since the overhead was a very small portion of the system, only a few cars would be so equipped. The changeover occurred at the grade crossing at East Prairie, the former site of 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 Oslo 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's 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.
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 300km/h (190mph), 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 (Brecknell Willis and 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 160km/h and higher.[citation needed] 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.
A tram is a type of urban rail transit consisting of either individual railcars or self-propelled multiple unit trains that run on tramway tracks on urban public streets; some include segments on segregated right-of-way. The tramlines or tram networks operated as public transport are called tramways or simply trams/streetcars. Due to their close similarities, trams are commonly included in the wider term light rail, which also includes systems separated from other traffic.
Light rail is a form of passenger urban rail transit using rolling stock derived from tram technology while also having some features from heavy rapid transit.
A trolleybus is an electric bus that draws power from dual overhead wires using spring-loaded trolley poles. Two wires, and two trolley poles, are required to complete the electrical circuit. This differs from a tram or streetcar, which normally uses the track as the return path, needing only one wire and one pole. They are also distinct from other kinds of electric buses, which usually rely on batteries. Power is most commonly supplied as 600-volt direct current, but there are exceptions.
An overhead line or overhead wire is an electrical cable that is used to transmit electrical energy to electric locomotives, electric multiple units, trolleybuses or trams. The generic term used by the International Union of Railways for the technology is overhead line. It is known variously as overhead catenary, overhead contact line (OCL), overhead contact system (OCS), overhead equipment (OHE), overhead line equipment, overhead lines (OHL), overhead wiring (OHW), traction wire, and trolley wire.
A third rail, also known as a live rail, electric rail or conductor rail, is a method of providing electric power to a railway locomotive or 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 fully segregated from the outside environment. Third-rail systems are usually supplied from direct current electricity.
The interurban is a type of electric railway, with tram-like electric self-propelled railcars which run within and between cities or towns. The term "interurban" is usually used in North America, with other terms used outside it. They were very prevalent in many parts of the world before the Second World War and were used primarily for passenger travel between cities and their surrounding suburban and rural communities. Interurban as a term encompassed the companies, their infrastructure, their cars that ran on the rails, and their service. In the United States, the early 1900s interurban was a valuable economic institution, when most roads between towns, many town streets were unpaved, and transportation and haulage was by horse-drawn carriages and carts.
Railway electrification is the use of electric power for the propulsion of rail transport. Electric railways use either electric locomotives, electric multiple units or both. Electricity is typically generated in large and relatively efficient generating stations, transmitted to the railway network and distributed to the trains. Some electric railways have their own dedicated generating stations and transmission lines, but most purchase power from an electric utility. The railway usually provides its own distribution lines, switches, and transformers.
A trolley pole is a tapered cylindrical pole of wood or metal, used to transfer electricity from a "live" (electrified) overhead wire to the control and the electric traction motors of a tram or trolley bus. It is a type of current collector. The use of overhead wire in a system of current collection is reputed to be the 1880 invention of Frank J. Sprague, but the first working trolley pole was developed and demonstrated by Charles Van Depoele, in autumn 1885.
Ground-level power supply, also known as surface current collection or, in French, alimentation par le sol, is a concept and group of technologies whereby electric vehicles collect electric power at ground level from individually-powered segments instead of the more common overhead lines. Ground-level power supply was developed for aesthetic reasons, to avoid the presence of overhead lines in city centres.
Conduit current collection is an obsolete system that was used by some electric tramways to pass current to streetcars via a "conduit", a small tunnel under the roadway. Modern systems fall under the term ground-level power supply.
Urban rail transit is a wide term for various types of local rail systems providing passenger service within and around urban or suburban areas. The set of urban rail systems can be roughly subdivided into the following categories, which sometimes overlap because some systems or lines have aspects of multiple types.
Various terms are used for passenger railway lines and equipment; the usage of these terms differs substantially between areas:
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 was replaced by the pantograph or the trolley pole, itself often later replaced by the pantograph.
Railway electric traction describes the various types of locomotive and multiple units that are used on electrification systems around the world.
The history of trams, streetcars, or trolleys began in the early nineteenth century. It can be divided up into several discrete periods defined by the principal means of motive power used.
The stud contact system is an obsolete ground-level power supply system for electric trams. Power supply studs were set in the road at intervals and connected to a buried electric cable by switches operated by magnets on the tramcars. Current was collected from the studs by a "skate" or "ski collector" under the tramcar. The system was popular for a while in the early 1900s but soon fell out of favour because of the unreliability of the magnetic switches, largely due to friction and rapid corrosion affecting its cast iron moving components.
A current collector is a device used in trolleybuses, trams, electric locomotives and EMUs to carry electric power (current) from overhead lines, electric third rails, or ground-level power supplies to the electrical equipment of the vehicles. Those for overhead wires are roof-mounted devices, those for rails are mounted on the bogies.
Three-phase AC railway electrification was used in Italy, Switzerland and the United States in the early twentieth century. Italy was the major user, from 1901 until 1976, although lines through two tunnels also used the system; the Simplon Tunnel between Switzerland and Italy from 1906 to 1930, and the Cascade Tunnel of the Great Northern Railway in the United States from 1909 to 1939. The first standard gauge line was in Switzerland, from Burgdorf to Thun, from 1899 to 1933.
References
Wikimedia Commons has media related to Pantograph .
↑ Steimel, Andreas (1 December 2007). Electric traction – motive power and energy supply: basics and practical experience. Munich: Oldenbourg Industrieverl. p.4. ISBN9783835631328.
↑ Krzysztof, Zintel (January 2005). "Wąskotorowe lokomotywy elektryczne na tor 900 mm w kopalniach węgla brunatnego". Świat Kolei (in Polish): 14–21. ISSN1234-5962.
↑ Meunier, Jacob (2001). The politics of high speed rail in France, 1944-1983. Westport, Conn.: Praeger. p.84. ISBN0275973778.
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