Misplaced Pages

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107-466: An overhead line consists of one or more wires (or rails , particularly in tunnels) situated over rail 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 a high-voltage electrical grid . Electric trains that collect their current from overhead lines use a device such as a pantograph , bow collector or trolley pole . It presses against

214-413: A block and tackle arrangement. Lines are divided into sections to limit the scope of an outage and to allow maintenance. 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

321-597: A gauge number or cross-sectional area . Wires are used to bear mechanical loads , often in the form of wire rope . In electricity and telecommunications signals , a "wire" can refer to an electrical cable , which can contain a "solid core" of a single wire or separate strands in stranded or braided forms. Usually cylindrical in geometry, wire can also be made in square, hexagonal, flattened rectangular, or other cross-sections, either for decorative purposes, or for technical purposes such as high-efficiency voice coils in loudspeakers . Edge-wound coil springs , such as

428-419: A swing 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

535-476: 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

642-485: A detent, like that in an automotive shoulder safety belt , which "catches" the rope to prevent the trolley pole from flying upward if the pole is dewired. The similar looking retriever (see photo) adds a spring mechanism that yanks the pole downward if it should leave the wire, pulling it away from all overhead wire fittings. Catchers are commonly used on trams operating at lower speeds, as in a city, whilst retrievers are used on suburban and interurban lines to limit damage to

749-514: A few months, Van Depoele switched to the trolley-pole system for the Montgomery operation. Van Depoele and fellow inventor Frank J. Sprague were "working on similar ideas at about the same time", and Sprague employed trolley-pole current collection on an electric streetcar system he installed in Richmond, Virginia, in 1888, also improving the trolley pole wheel and pole designs. Known as

856-535: A few others worldwide retain use of trolley poles, even on new streetcars, in order to avoid the difficulty and expense of modifying long stretches of existing overhead wires to accept pantographs. However, the Toronto Transit Commission , with the impending replacement of its legacy CLRV and ALRV with new Flexity Outlook cars, converted its overhead power supply to be compatible with both trolley poles and pantographs on an interim basis, as

963-411: 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 a ratchet mechanism) with a toothed rim, mounted on an arm hinged to the mast. Normally the downward pull of the weights and

1070-584: A grooved punch and a grooved metal anvil . Swaging is of great antiquity, possibly dating to the beginning of the 2nd millennium BCE in Egypt and in the Bronze and Iron Ages in Europe for torcs and fibulae . Twisted square-section wires are a very common filigree decoration in early Etruscan jewelry. In about the middle of the 2nd millennium BCE, a new category of decorative tube was introduced which imitated

1177-408: 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. Wire A wire is a flexible, round, bar of metal . Wires are commonly formed by drawing the metal through a hole in a die or draw plate . Wire gauges come in various standard sizes, as expressed in terms of

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1284-484: A level crossing with the 1,200 V DC Uetliberg 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. Many cities had trams and trolleybuses using trolley poles. They used insulated crossovers, which required tram drivers to put

1391-568: A line of granules. True beaded wire, produced by mechanically distorting a round-section wire, appeared in the Eastern Mediterranean and Italy in the seventh century BCE, perhaps disseminated by the Phoenicians . Beaded wire continued to be used in jewellery into modern times, although it largely fell out of favour in about the tenth century CE when two drawn round wires, twisted together to form what are termed 'ropes', provided

1498-440: A machine may have six bobbins on one cage and twelve on the other. Solid wire, also called solid-core or single-strand wire, consists of one piece of metal wire. Solid wire is useful for wiring breadboards. Solid wire is cheaper to manufacture than stranded wire and is used where there is little need for flexibility in the wire. Solid wire also provides mechanical ruggedness; and, because it has relatively less surface area which

1605-578: A multiple unit passes over them. In the United Kingdom equipment similar to Automatic Warning System (AWS) is used, but with pairs of magnets placed outside the 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

1712-403: A pneumatic servo pantograph with only 3  g acceleration. 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 a trolleybus or a trolleytruck , no rails are available for the return current, as the vehicles use rubber tyres on the road surface. Trolleybuses use

1819-427: A railway vehicle), a single trolley pole usually collects current from the overhead wire, and the steel rails on the tracks act as the electrical return . To reduce electrolytic corrosion of underground pipes and metallic structures, most tram lines are operated with the wire positive with respect to the rails. Trolleybuses , on the other hand, must use two trolley poles and dual overhead wires, one pole and wire for

1926-415: 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. 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 the messenger wire or catenary . This wire approximates

2033-414: A rigid overhead wire in their tunnels, while using normal overhead wires in their above ground sections. 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 last traction current pylon before the movable bridge). For example, the power supply can be done through a catenary wire system near

2140-467: A second parallel overhead line for the return, and two trolley poles , one contacting each overhead wire. ( Pantographs are generally incompatible with parallel overhead lines.) The circuit is completed by using both wires. Parallel overhead wires are also used on the rare railways with three-phase AC railway electrification . In the Soviet Union the following types of wires/cables were used. For

2247-467: 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

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2354-539: 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. Given limited clearance such as in tunnels , the overhead wire may be replaced by a rigid overhead rail. An early example was in the tunnels of the Baltimore Belt Line , where a Π section bar (fabricated from three strips of iron and mounted on wood)

2461-582: A simpler-to-make alternative. A forerunner to beaded wire may be the notched strips and wires which first occur from around 2000 BCE in Anatolia . Wire was drawn in England from the medieval period. The wire was used to make wool cards and pins, manufactured goods whose import was prohibited by Edward IV in 1463. The first wire mill in Great Britain was established at Tintern in about 1568 by

2568-432: A solid wire of the same diameter because the cross-section of the stranded wire is not all copper; there are unavoidable gaps between the strands (this is the circle packing problem for circles within a circle ). A stranded wire with the same cross-section of conductor as a solid wire is said to have the same equivalent gauge and is always a larger diameter. However, for many high-frequency applications, proximity effect

2675-440: A sprung base on the roof of the vehicle, with springs providing the pressure to keep the trolley wheel or shoe in contact with the wire. If the pole is made of wood, a cable brings the electric current down to the vehicle. A metal pole may use such a cable, or may itself be electrically "live", requiring the base to be insulated from the vehicle body. On systems with double-ended tram cars capable of running in both directions,

2782-467: 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. An early development of an experimental tramway in Toronto , Ontario , was built in 1883, having been developed by John Joseph Wright , brother of swindler Whitaker Wright . While Wright may have assisted in

2889-476: 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 at tram stops as for the Combino Supra . Trams draw their power from a single overhead wire at about 500 to 750  V DC. Trolleybuses draw from two overhead wires at a similar voltage, and at least one of

2996-701: A tramway. The tramway operated on 600–700 V DC and the railway on 15 kV AC . In the Swiss village of Oberentfelden , the Menziken–Aarau–Schöftland line operating at 750 V DC crosses the SBB line at 15 kV AC; there used to be a similar crossing between the two lines at Suhr but this was replaced by an underpass in 2010. Some crossings between tramway/light rail and railways are extant in Germany. In Zürich , Switzerland, VBZ trolleybus line 32 has

3103-570: A witch astride— The string you see to her leg is tied. In 1947, composer Samuel Barber wrote the now-classic orchestral and vocal piece Knoxville: Summer of 1915 , based on the childhood reminiscences of James Agee . Partway through the composition, the singer refers to a noisy passing streetcar, with its overhead trolley pole and sparks: A streetcar raising into iron moan; stopping; belling and starting, stertorous; rousing and raising again its iron increasing moan and swimming its gold windows and straw seats on past and past and past,

3210-401: Is a 2/0 wire made from 5,292 strands of No. 36 gauge wire. The strands are organized by first creating a bundle of 7 strands. Then 7 of these bundles are put together into super bundles. Finally 108 super bundles are used to make the final cable. Each group of wires is wound in a helix so that when the wire is flexed, the part of a bundle that is stretched moves around the helix to a part that

3317-475: Is a matter of raising one and lowering the other. Since the operator could raise the pole at one end whilst the conductor lowered the other, this saved time and was much easier for the conductor. Care had to be taken to raise the downed pole first, to eliminate the damage caused by arcing between the pole and wire. In the US, the dual-pole system was the most common arrangement on double-ended vehicles. However, pushing of

Overhead line - Misplaced Pages Continue

3424-422: 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

3531-494: Is compressed to allow the wire to have less stress. Prefused wire is stranded wire made up of strands that are heavily tinned , then fused together. Prefused wire has many of the properties of solid wire, except it is less likely to break. A braided wire consists of a number of small strands of wire braided together. Braided wires do not break easily when flexed. Braided wires are often suitable as an electromagnetic shield in noise-reduction cables. Wire has many uses. It forms

3638-453: Is exposed to attack by corrosives, protection against the environment. Stranded wire is composed of a number of small wires bundled or wrapped together to form a larger conductor. Stranded wire is more flexible than solid wire of the same total cross-sectional area. Stranded wire is used when higher resistance to metal fatigue is required. Such situations include connections between circuit boards in multi-printed-circuit-board devices, where

3745-408: Is in no less demand for fencing, and much is consumed in the construction of suspension bridges , and cages, etc. In the manufacture of stringed musical instruments and scientific instruments, wire is again largely used. Carbon and stainless spring steel wire have significant applications in engineered springs for critical automotive or industrial manufactured parts/components. Pin and hairpin making;

3852-417: Is in use, standard sizes for contact wire are 100 and 150 mm. The catenary wire is made of copper or copper alloys of 70, 120 or 150 mm. 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 mm and one or two catenary wires of 120 mm, totaling 320 or 440 mm. Only one contact wire

3959-414: 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-mounted transducer on the train which causes a large electrical circuit-breaker to open and close when the locomotive or the pantograph vehicle of

4066-485: Is more severe than skin effect, and in some limited cases, simple stranded wire can reduce proximity effect. For better performance at high frequencies, litz wire , which has the individual strands insulated and twisted in special patterns, may be used. The more individual wire strands in a wire bundle, the more flexible, kink-resistant, break-resistant, and stronger the wire becomes. However, more strands increases manufacturing complexity and cost. For geometrical reasons ,

4173-620: Is nowadays done by passing them through an extruder. Formerly, materials used for insulation included treated cloth or paper and various oil-based products. Since the mid-1960s, plastic and polymers exhibiting properties similar to rubber have predominated. Two or more wires may be wrapped concentrically, separated by insulation, to form coaxial cable . The wire or cable may be further protected with substances like paraffin , some kind of preservative compound, bitumen, lead , aluminum sheathing, or steel taping. Stranding or covering machines wind material onto wire which passes through quickly. Some of

4280-448: Is often used for side tracks. In the UK and EU 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 mm. 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

4387-585: Is only from these and certain of their alloys with other metals, principally brass and bronze , that wire is prepared. By careful treatment, extremely thin wire can be produced. Special purpose wire is however made from other metals (e.g. tungsten wire for light bulb and vacuum tube filaments, because of its high melting temperature). Copper wires are also plated with other metals, such as tin, nickel, and silver to handle different temperatures, provide lubrication, and provide easier stripping of rubber insulation from copper. Metallic wires are often used for

Overhead line - Misplaced Pages Continue

4494-476: Is problematic for longer modern streetcars that draw more electricity than older streetcars. In Toronto, the trolley pole shoe contains a carbon insert to provide electrical contact with the overhead wire and to lower the shoe to clear overhead wire hangers. Carbon inserts wear out and must be periodically replaced. The trolley shoe inserts on Toronto's modern Flexity Outlook streetcars quickly wear out in rainy conditions, lasting as little as eight hours instead of

4601-421: 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

4708-463: Is the lowest that should be used (7 should only be used in applications where the wire is placed and then does not move), and 49 is much better. For applications with constant repeated movement, such as assembly robots and headphone wires, 70 to 100 is mandatory . For applications that need even more flexibility, even more strands are used (welding cables are the usual example, but also any application that needs to move wire in tight areas). One example

4815-1029: Is used only on the Gornergrat Railway and Jungfrau Railway in Switzerland, the Petit train de la Rhune in France, and the Corcovado Rack Railway in 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)),

4922-417: The skin effect , resulting in increased power loss in the wire. Stranded wire might seem to reduce this effect, since the total surface area of the strands is greater than the surface area of the equivalent solid wire, but ordinary stranded wire does not reduce the skin effect because all the strands are short-circuited together and behave as a single conductor. A stranded wire will have higher resistance than

5029-579: The Daugavpils, Latvia system , and Rio de Janeiro 's Santa Teresa Tramway . The MBTA system of Boston still uses trolley poles with the PCC streetcars it uses to serve the Ashmont–Mattapan High Speed Line . Trams or light rail cars equipped with pantographs normally cannot operate on lines with overhead wiring designed for trolley-pole collection. For this reason, these systems and

5136-514: The Richmond Union Passenger Railway , this 12-mile (19 km) system was the first large-scale trolley line in the world, opening to great fanfare on February 12, 1888. The grooved trolley wheel was used on many large city systems through the 1940s and 1950s; it was generally used on systems with "old" style round cross sectional overhead wire. The trolley wheel was problematic at best; the circumferential contact of

5243-457: The Slinky toy, are made of special flattened wire. In antiquity , jewelry often contains large amounts of wire in the form of chains and applied decoration that is accurately made and which must have been produced by some efficient, if not technically advanced, means. In some cases, strips cut from metal sheet were made into wire by pulling them through perforations in stone beads. This causes

5350-463: The tram or trolleybus must 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

5457-503: 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 the Level Crossing Removal Project . Athens has two crossings of tram and trolleybus wires, at Vas. Amalias Avenue and Vas. Olgas Avenue, and at Ardittou Street and Athanasiou Diakou Street. They use the above-mentioned solution. In Rome , at

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5564-571: The CLRVs and ALRVs use only trolley poles while the Flexity fleet is equipped for both trolley poles and pantographs. Large portions of San Francisco's surface network are also set up to handle both trolley pole and pantograph operation in order to allow for compatibility both with Muni's current fleet of light rail vehicles (pantograph only), as well as Muni's historic streetcar fleet (trolley pole only). Upon their introduction, trolley poles and

5671-521: The Hell's Gate Bridge boundary between Amtrak and Metro 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. 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

5778-441: The added wire may be circular in cross-section ("round-wound"), or flattened before winding ("flat-wound"). Examples include: Trolley pole 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

5885-565: 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. On the Pennsylvania 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

5992-429: The bobbins; the latter being revolved at a suitable speed bodily with their disks, the cotton is consequently served on to the wire, winding in spiral fashion so as to overlap. If many strands are required the disks are duplicated, so that as many as sixty spools may be carried, the second set of strands being laid over the first. For heavier cables that are used for electric light and power as well as submarine cables,

6099-611: The contact wire, cold drawn solid copper was used to ensure good conductivity . 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 mm. 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

6206-476: The controller into neutral and coast through. Trolleybus drivers had to either lift off the accelerator or switch to auxiliary power. In Melbourne , Victoria, tram drivers put the controller into neutral and coast through section insulators, indicated by insulator markings between the rails. Melbourne has several remaining level crossings between electrified suburban railways and tram lines. They have mechanical switching arrangements (changeover switch) to switch

6313-526: 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. In Milan , most tram lines cross its circular trolleybus line once or twice. Trolleybus and tram wires run parallel in streets such as viale Stelvio, viale Umbria and viale Tibaldi. Some railways used two or three overhead lines, usually to carry three-phase current. This

6420-797: The expected one to two days for shorter older streetcars. The extra current draw shortens the life of the carbon insert. A worn-out carbon insert would damage the overhead wire, stopping streetcar service. Apart from heritage streetcar lines, very few tram/streetcar systems worldwide continue to use trolley poles on vehicles used in normal service. Among the largest exceptions are the streetcar systems of New Orleans, Louisiana ; Toronto, Ontario ; Philadelphia (the "Subway-Surface" lines and Route 15 ); Riga, Latvia (however, new Škoda trams in Riga have pantographs); Kolkata (formerly Calcutta), India ; and Alexandria, Egypt . Smaller systems still using trolley poles for regular service include Hong Kong Tramways ,

6527-533: The founders of the Company of Mineral and Battery Works , who had a monopoly on this. Apart from their second wire mill at nearby Whitebrook, there were no other wire mills before the second half of the 17th century. Despite the existence of mills, the drawing of wire down to fine sizes continued to be done manually. According to a description in the early 20th century, "[w]ire is usually drawn of cylindrical form; but it may be made of any desired section by varying

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6634-479: The grooved wheel bearing on the underside of the overhead wire provided minimal electrical contact and tended to arc excessively, increasing overhead wire wear. The newer sliding carbon trolley shoe was generally used with a newer grooved overhead trolley wire of a roughly " figure 8 " cross section. The sliding trolley shoe provided better electrical contact (with a reduction in arcing), and it dramatically reduced overhead wire wear. Many systems began converting to

6741-551: The hole and then drifting it out to correct diameter with a punch." Wire is often reduced to the desired diameter and properties by repeated drawing through progressively smaller dies, or traditionally holes in draw plates . After a number of passes the wire may be annealed to facilitate more drawing or, if it is a finished product, to maximise ductility and conductivity . Electrical wires are usually covered with insulating materials , such as plastic, rubber-like polymers, or varnish. Insulating and jacketing of wires and cables

6848-431: The hollow shaft. This disk has perforations through which each of the strands pass, thence being immediately wrapped on the cable, which slides through a bearing at this point. Toothed gears having certain definite ratios are used to cause the winding drum for the cable and the cage for the spools to rotate at suitable relative speeds which do not vary. The cages are multiplied for stranding with many tapes or strands, so that

6955-563: The installation of electric railways at the Canadian National Exhibition (CNE), and may even have used a pole system, there is no evidence about this. Likewise, Wright never filed or was issued a patent. Credit for development of the first working trolley pole is given to Charles Joseph Van Depoele , a Belgian engineer who moved to the United States in 1869. Van Depoele made the first public demonstration of

7062-451: 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, the arc generated across the pantograph can damage the pantograph, the catenary insulator or both. 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

7169-432: The lower-pitched sound-producing "strings" in stringed instruments , such as violins , cellos , and guitars , and percussive string instruments such as pianos , dulcimers , dobros , and cimbaloms . To increase the mass per unit length (and thus lower the pitch of the sound even further), the main wire may sometimes be helically wrapped with another, finer strand of wire. Such musical strings are said to be "overspun";

7276-416: The lowest number of strands usually seen is 7: one in the middle, with 6 surrounding it in close contact. The next level up is 19, which is another layer of 12 strands on top of the 7. After that the number varies, but 37 and 49 are common, then in the 70 to 100 range (the number is no longer exact). Larger numbers than that are typically found only in very large cables. For application where the wire moves, 19

7383-408: The machines are somewhat different in construction. The wire is still carried through a hollow shaft, but the bobbins or spools of covering material are set with their spindles at right angles to the axis of the wire, and they lie in a circular cage which rotates on rollers below. The various strands coming from the spools at various parts of the circumference of the cage all lead to a disk at the end of

7490-482: 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 avoid galvanic corrosion of metallic parts near the railway, such as on the Chemin de fer de la Mure . All systems with multiple overhead lines have

7597-409: The natural path of a wire strung between two points, a catenary 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 a pulley , link or clamp . The whole system is then subjected to mechanical tension . As

7704-403: The need to manually turn the trolley pole when changing direction (although this disadvantage can be overcome to some extent through the use of trolley reversers). The use of pantographs (or bow collectors) exclusively also eliminates the need for wire frogs (switches in the overhead wiring) to make sure the pole goes in the correct direction at junctions. The trolley pole with a shoe at its tip

7811-520: The needle and fish-hook industries; nail, peg, and rivet making; and carding machinery consume large amounts of wire as feedstock. Not all metals and metallic alloys possess the physical properties necessary to make useful wire. The metals must in the first place be ductile and strong in tension, the quality on which the utility of wire principally depends. The principal metals suitable for wire, possessing almost equal ductility, are platinum , silver , iron , copper , aluminium, and gold ; and it

7918-466: The new electrical technology they represented were fascinating to writers, with their lightning -like sparks and power. In January 1889, Boston introduced its first electric streetcars, which became so popular and noteworthy that poet Oliver Wendell Holmes composed a verse about the new trolley pole technology, and the sparking contact shoe at its apex: Since then on many a car you'll see A broomstick as plain as plain can be; On every stick there's

8025-538: The outline of the holes in the draw-plate through which it is passed in the process of manufacture. The draw-plate or die is a piece of hard cast-iron or hard steel, or for fine work it may be a diamond or a ruby . The object of utilising precious stones is to enable the dies to be used for a considerable period without losing their size, and so producing wire of incorrect diameter. Diamond dies must be re-bored when they have lost their original diameter of hole, but metal dies are brought down to size again by hammering up

8132-438: The overhead at speed. On some older systems, the poles were raised and lowered using a long pole with a metal hook. Where available, these may have been made of bamboo due to its length, natural straightness and strength, combined with its relative light weight and the fact that it is an insulator. Trolleybuses usually carried one with the vehicle, for use in the event of dewirement, but tram systems usually had them placed along

8239-402: 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

8346-482: 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 most 25 kV OHL 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,

8453-455: 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. For tramways , 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

8560-457: The pantograph causes mechanical oscillations in the wire. The waves must travel faster than the train to avoid producing standing 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

8667-411: 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 is zigzagged slightly 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

8774-424: 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 for DC systems. AC systems have a particular safety implication in that the railway electrification system would act as

8881-500: The pole (called "back-poling" in the US or "spear-poling" in Australia), was quite common where the trams were moving at slow speeds, such as at wye terminals (also known as reversers) and whilst backing into the sheds. Trolley poles are usually raised and lowered manually by a rope from the back of the vehicle. The rope feeds into a spring reel mechanism, called a "trolley catcher" or "trolley retriever". The trolley catcher contains

8988-615: The positive "live" current, the other for the negative or neutral return . The tramway system in Havana , Cuba , also utilized the dual-wire system, as did the Cincinnati, Ohio streetcar system . All trolleybuses use trolley poles, and thus trolley poles remain in use worldwide, wherever trolleybuses are in operation (some 315 cities as of 2011 ), and several manufacturers continue to make them, including Kiepe , Škoda and Lekov . However, on most railway vehicles using overhead wire,

9095-579: The raw material of many important manufacturers , such as the wire netting industry, engineered springs, wire-cloth making and wire rope spinning, in which it occupies a place analogous to a textile fiber . Wire-cloth of all degrees of strength and fineness of mesh is used for sifting and screening machinery, for draining paper pulp, for window screens, and for many other purposes. Vast quantities of aluminium , copper , nickel and steel wire are employed for telephone and data cables , and as conductors in electric power transmission , and heating . It

9202-519: 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

9309-416: The rigidity of solid wire would produce too much stress as a result of movement during assembly or servicing; A.C. line cords for appliances; musical instrument cables; computer mouse cables; welding electrode cables; control cables connecting moving machine parts; mining machine cables; trailing machine cables; and numerous others. At high frequencies, current travels near the surface of the wire because of

9416-410: The route at locations where the trolley pole would need reversing. The poles used on trolleybuses are typically longer than those used on trams, to allow the bus to take fuller advantage of its not being restricted to a fixed path in the street (the rails), by giving a degree of lateral steerability, enabling the trolleybus to board passengers at curbside. When used on a tram or trolley car (i.e.

9523-408: The sliding trolley shoe in the 1920s; Milwaukee, Wisconsin converted its large system in the late 1920s. Philadelphia did not convert its trolley wheels on its remaining streetcars until 1978. Although a streetcar with a trolley wheel may evoke an antique look, the trolley shoe is modern and more practical as well as economical. A trolley pole is not attached to the overhead wire. The pole sits atop

9630-430: The smallest machines for cotton covering have a large drum, which grips the wire and moves it through toothed gears; the wire passes through the centre of disks mounted above a long bed, and the disks carry each a number of bobbins varying from six to twelve or more in different machines. A supply of covering material is wound on each bobbin, and the end is led on to the wire, which occupies a central position relatively to

9737-685: The spring-loaded device on a temporary streetcar line installed at the Toronto Industrial Exhibition (now the CNE) in autumn 1885. Depoele's first trolley pole was "crude" and not very reliable, and he reverted to using the troller system of current collection for a commercial installation on a streetcar system in South Bend, Indiana, which opened on November 14, 1885, and on one in Montgomery, Alabama, in April 1886. However, within

9844-420: 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

9951-487: 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. In Slovenia , where 3 kV system

10058-420: The strip wire drawing method. The strip twist wire manufacturing method was superseded by drawing in the ancient Old World sometime between about the 8th and 10th centuries AD. There is some evidence for the use of drawing further East prior to this period. Square and hexagonal wires were possibly made using a swaging technique. In this method a metal rod was struck between grooved metal blocks, or between

10165-494: The strips to fold round on themselves to form thin tubes. This strip drawing technique was in use in Egypt by the 2nd Dynasty ( c.  2890  – c.  2686  BCE ). From the middle of the 2nd millennium BCE most of the gold wires in jewelry are characterized by seam lines that follow a spiral path along the wire. Such twisted strips can be converted into solid round wires by rolling them between flat surfaces or

10272-514: The tension is virtually independent of temperature. Tensions are typically between 9 and 20  kN (2,000 and 4,500  lbf ) 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

10379-470: 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 of insulating material extending 20 or 30 mm (0.79 or 1.18 in) below. Until 1946, a level crossing in Stockholm , Sweden connected the railway south of Stockholm Central Station and

10486-405: The trolley pole has given way to the bow collector or, later, the pantograph , a folding metal device that presses a wide contact pan against the overhead wire. While more complex than the trolley pole, the pantograph has the advantage of being almost free from dewiring, being more stable at high speed, and being easier to raise and lower automatically. Also, on double-ended trams , they eliminate

10593-424: The trolley pole must always be pulled behind the car and not pushed, or "dewiring" is very likely, which can cause damage to the overhead wires. At terminus points, the conductor must turn the trolley pole around to face the correct direction, pulling it off the wire either with a rope or a pole and walking it around to the other end. In some cases, two trolley poles are provided, one for each direction: in this case it

10700-444: The trolleybus wires must be insulated from tram wires. This is usually done by the trolleybus wires running continuously through the crossing, with the tram conductors a 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

10807-639: 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-electric locomotives (such as diesels ) may pass along these tracks without affecting the overhead line, although there may be difficulties with overhead clearance . Alternative electrical power transmission schemes for trains include third rail , ground-level power supply , batteries and electromagnetic induction . Vehicles like buses that have rubber tyres cannot provide

10914-405: 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. Catenary wires are kept in mechanical tension because

11021-499: 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

11128-729: Was originally devised by the Pennsylvania Railroad and was continued by Amtrak and adopted by Metro North . Metal signs were hung from the catenary supports with the letters "PB" created by a pattern of drilled holes. 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,

11235-429: Was possible only at low speeds, using a single wire. To enable higher speeds, two additional types of equipment were developed: 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

11342-488: 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

11449-467: Was used, with the brass contact running inside the groove. When the overhead line was raised in the Simplon Tunnel to 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 on moveable bridges . In modern uses, it is very common for underground sections of trams, metros, and mainline railways to use

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