NationMaster - Encyclopedia: Overhead wire

An electric multiple unit pulling into Tile Hill station on the West Coast Main Line in Coventry, England. Photo by G-Man 2003 (newer version) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. Click on date to download...

An electric multiple unit pulling into Tile Hill station; Coventry, England. Note the overhead line!

Overhead lines or overhead wires are used to transmit Electrical energy or Electromagnetic energy is a form of energy present in any electric field or magnetic field, or in any volume containing electromagnetic radiation. The SI unit of electrical energy is the joule, while the unit used by electrical utility companies is the watt-hour (Wh) or the kilowatt... electrical energy to A train of Light Rail, KCRC, Hong Kong. A METRORail train approaching Preston Station in downtown Houston, Texas, USA. The O-Train, the diesel light-rail metro service for Ottawa, Ontario, Canada. A Hiawatha Line train near Cedar-Riverside station in Minneapolis. A Citadis tram in Melbourne, Australia. A Hudson... trams, A trolleybus in Arnhem An electric trolleybus (also known as trolley bus or trackless trolley or simply trolley) is a bus powered by two overhead electric wires, from which the bus draws electricity using two trolley poles. Two poles are required in order to accommodate the return current, which can... trolleybusses, or An electric multiple unit pulling into Tile Hill station; Coventry, England In rail transport, a train consists of a single or several connected rail vehicles that are capable of being moved together along a guideway to transport freight or passengers from one place to another along a planned route. The... trains at a distance from the energy supply point. These overhead lines are known variously as

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 Railroad or railway tracks are used on railways, which, together with railroad switches (points), guide trains without the need for steering. Tracks consist of two parallel steel rails, which are laid and fastened upon sleepers (or cross ties) which are embedded in ballast to form the railroad track. Rails, being... rail tracks, raised to a high electrical potential by connection to feeder stations at regular intervals. The feeder stations are usually fed from a The difference between high voltage and low voltage depends on the situation and on the field of science or industry involved. Laypeople generally consider mains to be high voltage largely because it is the highest voltage they normally encounter. The UKs Institution of Electrical Engineers defines high voltage as... high voltage electrical grid.

Construction

As an electric train passes under the lowest wire, known as the contact wire, a device on the train roof called the Categories: Rail stubs | Rail technologies ... pantograph makes contact with the wire ( A train of Light Rail, KCRC, Hong Kong. A METRORail train approaching Preston Station in downtown Houston, Texas, USA. The O-Train, the diesel light-rail metro service for Ottawa, Ontario, Canada. A Hiawatha Line train near Cedar-Riverside station in Minneapolis. A Citadis tram in Melbourne, Australia. A Hudson... trams generally use Categories: Rail stubs | Rail technologies ... pantographs as well but sometimes use bow collectors, or 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. This system of current collection was an invention of Frank J. Sprague. Origin of the term... trolleypoles). The pantograph, bow collector, or trolleypole is electrically conductive, and allows current to flow towards The term ground (or earth) usually means a common return in circuits. Meanings In electrical engineering, the term ) can be as simple as a metal rod or stake driven into the earth (usually copper), or a connection to buried metal water piping. Or it can be a complex system of... earth. This path takes the current through the traction motors of the train or tram, and back to the feeder station via the steel wheels and one or both track running rails. Diesel is a product used as a fuel in a diesel engine invented by Rudolf Diesel, and perfected by Charles F. Kettering. Petrodiesel One can obtain diesel from petroleum, which is called petrodiesel to distinguish it from diesel obtained from other sources. As a hydrocarbon mixture, it is obtained in... Diesel trains may pass along these tracks without affecting the overhead line, although clearance may be an issue.

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. This 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 shape, 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 A pulley is a wheel with a groove along its edge, for holding a rope or cable. Pulleys are usually used in sets designed to reduce the amount of force needed to lift a load. However, the same amount of work is necessary for the load to reach the same... pulley, link, or A group portrait of CLAMP. , formerly Nanase Ohkawa (, , a magazine specializing in events of the anime and manga subcultures, reported that the members of CLAMP simply wanted to try out new names. CLAMP Works In Progress Works Completed Works Unpublished Short Works These are short works that were only available... clamp. The whole system is then subjected to a mechanical In physics, tension is a force on a body directed to produce strain (extension); it can be considered to be negative compression. It is measured in according units (newton, dynes, pounds-force, etc). Tension is the dominant static force acting on such objects as a vibrating string or a stretched... tension. Such a system, with a single supporting wire, is known as simple equipment.

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 street A train of Light Rail, KCRC, Hong Kong. A METRORail train approaching Preston Station in downtown Houston, Texas, USA. The O-Train, the diesel light-rail metro service for Ottawa, Ontario, Canada. A Hiawatha Line train near Cedar-Riverside station in Minneapolis. A Citadis tram in Melbourne, Australia. A Hudson... tramways there often is just a simple contact wire and no message wire.

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 In physics, the newton (symbol: N) is the SI unit of force, named after Sir Isaac Newton in recognition of his work on classical mechanics. It was first used around 1904, but not until 1948 was it officially adopted by the General Conference on Weights and Measures (CGPM) as the... kN per wire.

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 equipment in the UK the maximum tension length for 25kV OHL is 1970 metre The metre is the basic unit of length in the International System of Units. It is defined as the length of the path traveled by light in an absolute vacuum during a time interval of 1/299,792,458 of a second. It is equal to 10000/254 inches... metres.

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 introduced close to the centre of the tension length to restrict movement. MPA's 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 Great Western Railway No. 6833 - it is easier to maintain one locomotive than many self-propelled cars. - should the locomotive break down, it is easy to replace it with a new one. Failure of the motive power unit does not require taking the whole train out of service. - separating the... locomotive's pantograph is in continual contact with the wire.

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, but this can be broken for servicing.

On overhead wires designed for trolleypoles this is done by having a neutral section between the wires, but this requires an insulator. The driver of the A train of Light Rail, KCRC, Hong Kong. A METRORail train approaching Preston Station in downtown Houston, Texas, USA. The O-Train, the diesel light-rail metro service for Ottawa, Ontario, Canada. A Hiawatha Line train near Cedar-Riverside station in Minneapolis. A Citadis tram in Melbourne, Australia. A Hudson... tramcar must turn off the power when the trolleypole passes through to prevent arcing from burning-out the insulator.

Sometimes on a larger electrified railway, tramway, or trollebusway, 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 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. Normal instructions are to put the controller (throttle) into neutral and coast through an isolated phase break section.

On the The Pennsylvania Railroad (AAR reporting mark: PRR) was an American railroad existing 1846–1968, after which it merged into Penn Central Transportation. Commonly referred to as the Pennsy, the company was headquartered in Philadelphia, Pennsylvania. The companys symbol was a keystone (Pennsylvanias symbol) with the letters PRR... Pennsylvania Railroad, phase breaks were indicated to train crews by a metal sign hung in the overhead with the letters PB on it, created by holes drilled in the metal. When the phase break is "dead", a signal consisting of eight lit lights in a circular pattern indicates this to the crew.

Crossings

Looking directly upward at a crossing in Bahnhofplatz, The city of Bern, English traditionally Berne [bɝːn] (German , a secret language used in the former workers quarter in German) he had killed. It was made a free imperial city by the Holy Roman Emperor Frederick II in 1218 after Berthold died without an heir. In 1353... Bern, The Swiss Confederation or Switzerland is a landlocked federal state in Europe, with neighbours Germany, France, Italy, Austria and Liechtenstein. The country has a strong tradition of political and military neutrality, but also of international co-operation, and is home to many international organisations. Confoederatio Helvetica (CH), the Latin version... Switzerland in 2002 September.

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

A train of Light Rail, KCRC, Hong Kong. A METRORail train approaching Preston Station in downtown Houston, Texas, USA. The O-Train, the diesel light-rail metro service for Ottawa, Ontario, Canada. A Hiawatha Line train near Cedar-Riverside station in Minneapolis. A Citadis tram in Melbourne, Australia. A Hudson... Trams draw their power from a single overhead wire at about 500 The volt is the SI derived unit for electric potential and voltage (derived from the ampere and watt). It is named in honor of Alessandro Volta, who, in 1800, invented the voltaic pile, the first chemical battery. The volt is defined as the potential difference across a conductor when a... volts above The term ground (or earth) usually means a common return in circuits. Meanings In electrical engineering, the term ) can be as simple as a metal rod or stake driven into the earth (usually copper), or a connection to buried metal water piping. Or it can be a complex system of... earth. A trolleybus in Arnhem An electric trolleybus (also known as trolley bus or trackless trolley or simply trolley) is a bus powered by two overhead electric wires, from which the bus draws electricity using two trolley poles. Two poles are required in order to accommodate the return current, which can... Trolley busses draw their power from two overhead wires with about 500 volts between them. So where the two cross, they must not touch.

The first requirement for this to work is that the trams must have pantograph-type power collection. Where the trams use a 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. This system of current collection was an invention of Frank J. Sprague. Origin of the term... trolley pole to collect their power, a different crossing style must be used.

The trolley bus wires run continuously through the crossing - they need to anyway because of the 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. This system of current collection was an invention of Frank J. Sprague. Origin of the term... trolley wheel pickup method. The tram En [ [ ciencia ] ] y [ [ ingeniería ] ], los conductores son los materiales de los cuales contenga las cargas movibles [ [ electricidad ] ]. Cuando una diferencia potencial eléctrica se impresiona a través de puntos separados en un conductor, las cargas móviles dentro del conductor se fuerzan para moverse, y una corriente el... conductors are slung a few centimetres lower than the trolley bus wires. Close to the junction on each side, the wire merges into a solid bar which is angled to run parallel to the trolley bus wires for about half a metre. Another bar similarly angled at its ends is hung between the trolley bus wires. This is electrically connected above to the tram wire's Catenary is a system of overhead wires used to supply electrical power to a locomotive, streetcar, or light rail vehicle. Unlike simple overhead wire, 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... catenary cable. The tram's pantograph will easily bridge over between these different conductor sections providing it with a continuous pickup.

Where the tram wire crosses, the trolley bus wires are protected by an inverted trough of Insulators are materials which prevent the flow of heat (thermal insulators) or electric charge (electrical insulators). The opposite of electrical insulators are conductors and semiconductors, which permit the flow of charge (Note: a semiconductor is strictly speaking also an insulator, since it prevents the flow of electric charge at low... insulating material extending 2 or 3 cm below the level of the trolley bus wires. The tram pantograph 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 ever touching the trolley bus wires.

Australia

Adelaide is the capital city of the Australian state of South Australia. It is a coastal city on the Southern Ocean and was named in honour of Queen Adelaide, the consort of King William IV. It is situated on the Fleurieu Peninsula overlooking the Gulf St. Vincent, bordered by the... Adelaide, Motto: , skippered by Francois Thijssen, examined the coastline. Thijssen named his discovery Pieter Nuyts Land, after the highest ranking individual on board. The coastline of South Australia was first mapped by Matthew Flinders and Nicolas Baudin in 1802. However, South Australia was only established as a commercial venture in 1831... South Australia once had trams and trolleybusses (and 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 auxilliary power.

In The City of Melbournes coat of arms The central business district of Melbourne, viewed from the north which means we gather strength as we go. Melbourne has twice ranked first in a survey by History of Melbourne Melbourne was founded on 10 May 1835 by a group of free... Melbourne, Motto: History of Victoria After the founding of the colony of New South Wales in 1788, the continent was divided into an eastern half - named New South Wales, and a western half, named New Holland, but under the administration of the colonial government in Sydney. Victorias first settlement was... 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.

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 1500V DC overhead for the railway and 650V 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 deviated.

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Tensioning

Breaks

Crossings

Australia

See also

Construction