Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point. These overhead lines are known variously as
- Overhead contact system (OCS)—Europe, except UK and Spain Lenovo S10-2 Battery 5200mAh
- Overhead line equipment (OLE or OHLE)—UK
- Overhead equipment (OHE) — UK, India, Pakistan and Malaysia
- Overhead wiring (OHW)—Australia Lenovo Y730 Battery 5200mAh
- Catenary—United States, India, UK, Singapore (North East MRT Line) , Canada and Spain.
In this article the generic term overhead line is used Lenovo Y710 Battery 5200mAh .
Overhead line is designed on the principle of one or more overhead wires or rails (particularly in tunnels) situated over rail tracks, raised to a high electrical potential by connection to feeder stations at regular intervals. The feeder stations are usually fed from a high-voltage electrical grid Lenovo Y530 Battery 5200mAh .
Electric trains that collect their current from an overhead line system use a device such as a pantograph, bow collector, or trolley pole. The device presses against the underside of the lowest wire of an overhead line system, the contact wire Lenovo Y510 Battery 5200mAh .
The 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 trains (such as diesels) may pass along these tracks without affecting the overhead line, although there may be difficulties with overhead clearance Lenovo S10-3 Battery 5200mAh .
Alternative electrical power transmission schemes for trains include third rail, Aesthetic Power Supply, batteries, and electromagnetic induction.
This article does not cover regenerative braking, where the traction motors act as generators to retard movement and return power to the overhead Lenovo G450 Battery 5200mAh .
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 above by a second wire known as the messenger wire (US & Canada) or catenary(UK) Lenovo E30 Battery 5200mAh .
This wire approximates 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 Lenovo E40 Battery 5200mAh .
The messenger wire is supported regularly at structures, by a pulley, link, or clamp. The whole system is then subjected to a mechanical tension.
As the contact wire makes contact with the pantograph, the carbon surface of the insert on top of the pantograph is worn downLenovo E50 Battery 5200mAh .
Going around a curve, the "straight" wire between supports will cause the contact wire to cross over the whole surface of the pantograph as the train travels around the curve, causing an even wear and avoiding any notches Lenovo G460 Battery 5200mAh .
On straight track, the contact wire is zigzagged slightly to the left and right of centre at each successive support so that the pantograph wears evenly.
The zigzagging of the overhead line is not required for trams using trolley poles or for trolleybuses Lenovo Y460 Battery 5200mAh .
Depot areas tend to have only a single wire and are known as simple equipment. When overhead line systems were first conceived, good current collection was possible only at low speeds, using a single wire. To enable higher speeds, two additional types of equipment were developed Lenovo Y450 Battery 5200mAh :
- Stitched equipment uses an additional wire at each support structure, terminated on either side of the messenger wire.
- Compound equipment uses a second support wire, known as the auxiliary, between the messenger wire and the contact wire Lenovo N200 Battery 5200mAh .
- Droppers support the auxiliary from the messenger wire, and additional droppers support the contact wire from the auxiliary. The auxiliary wire can be constructed of a more conductive but less wear-resistant metal, increasing the efficiency of power transmission Lenovo T410 Battery 5200mAh .
Dropper wires traditionally only provide physical support of the contact wire, and do not join the catenary and contact wires electrically. Contemporary systems use current-carrying droppers, which eliminate the need for separate wires Lenovo T510 Battery 5200mAh .
The present transmission system originated about 100 years ago. A simpler system was proposed in the 1970s by the Pirelli Construction Co 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 Lenovo SL410 Battery 5200mAh .
With a somewhat higher tension than used before clipping the beam yielded a deflected profile for the wire which could be easily handled at 250 miles per hour (400 km/h) by a pneumatic servo pantograph with only 3 G accelerations Lenovo SL510 Battery 5200mAh .
This cut about 40% from the total track overhead equipment cost but required a pantograph development period which was not accepted by British Rail.
For tramways there is often just a simple contact wire and no messenger wire Lenovo C100 Battery 5200mAh .
In situations where there is limited clearance to accommodate wire suspensions systems such as in tunnels, the overhead wire may be replaced by rigid overhead rail. This was done when the overhead line had to be raised in the Simplon Tunnel to accommodate taller rail vehicles Lenovo T400S Battery 5200mAh .
Parallel overhead lines
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 Lenovo Y430 Battery 5200mAh .
For a trolleybus there are no rails to send the return current along—the vehicles use rubber tyres and the normal road surface. Trolleybuses use a second parallel overhead line for the return, and two trolley-poles, one contacting each overhead wire. The circuit is completed by using both wires Ibm ThinkPad G40 Battery 5200mAh .
In Germany there are special overhead power lines for single phase AC traction current with a frequency of 16? hertz. All operate at a voltage of 110 kV (the voltage of the railway overhead lines is 15 kV) and have four conductor cables for two circuits Ibm ThinkPad X200T Battery 5200mAh .
As a rule at traction current lines, a single-level arrangement of conductor cables is used.
A traction current pylon is a type of electricity pylon with at least one electric circuit for traction current Apple A1280 battery 5200mAh
For traction current lines with four circuits (eight conductor cables) usually two-level arrangements of conductors are used, in which one pylon crossbar carries four conductor cables. For traction current lines used to supply high-speed rail tracks, three-level arrangements of conductors are employed Apple A1281 battery 5200mAh ;
thereby four conductor cables are mounted on the lowest crossbar, and two on the upper crossbars. The three-level arrangement is also used for traction current lines with six electric circuits (12 conductor cables) Samsung R522 battery 5200mAh .
There are other overhead line pylons with crossbars for 110 kV traction voltage. For example the power supplies of rapid transit railways. Additionally there are pylons that transmit both electric power for railway traction current as well as three-phase alternating current for the public power grid Samsung P467 battery 5200mAh .
Catenary wires are kept at a mechanical tension because the pantograph causes oscillations in the wire and thewave must travel faster than the train to avoid producing standing waves that would cause the wires to break. Tensioning the line makes waves travel faster Hp Pavilion dm3 Battery 5400mAh .
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), or constant tension and ensures that the tension in the equipment is virtually independent of temperature Hp Pavilion dm4 Battery 5200mAh .
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 stop the weights from swaying Hp Pavilion cq62 Battery 5200mAh .
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 (2,200 lbf). This type of equipment will sag on hot days and hog on cold days Hp Pavilion cq42 Battery 5200mAh .
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 Hp Pavilion cq72 Battery 5200mAh .
This leads to the concept of maximum tension length. For most 25 kV OHL equipment in the UK, the maximum tension length is 1970 m.
An additional issue with AT equipment is that, if balance weights are attached to both ends, the whole tension length will be free to move along track Hp cq20 Battery 2600mAh .
To rectify this issue, a midpoint anchor (MPA), close to the centre of the tension length, restricts movement of the messenger 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 Hp 2230 Battery 2600mAh ;
otherwise, they are anchored to the typical vertical catenary poles or portal catenary supports. Therefore, a tension length can be seen as a fixed centre point, with the two half tension lengths expanding and contracting with temperature Dell Inspiron Mini 12 battery 7800mAh .
Most overhead systems include a brake to stop the wires from unravelling completely should a wire break or tension be lost for any other reason. German systems usually use a single large tensioning pulley with a toothed rim, mounted on an arm hinged to the mastDell XPS M1730 battery 7800mAh .
Normally the downward pull of the weights, and the reactive upward pull of the tensioned wires, lifts 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 Dell XPS M2010 battery 7800mAh .
If a wire breaks or tension is otherwise lost, the pulley falls back toward the mast, and one of its teeth will jam against the stop. This stops further rotation, limits the damage, and keeps the undamaged part of the wire intact until it can be repaired Dell Studio XPS 1340 battery 5200mAh/7800mAh .
Other systems use various other braking mechanisms, usually with multiple smaller pulleys in a block and tackle arrangement.
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 Dell Inspiron 9100 battery 7800mAh.
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 locomotive's pantograph is in continuous contact with the wire Dell Inspiron N4010 battery 5200mAh .
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 Dell Inspiron N3610 battery 5200mAh .
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 (to different substations if at or near the halfway mark between them) but this can be broken for servicing Dell Inspiron N5010 battery 5200mAh .
On overhead wires designed for trolley poles this is done by having a neutral section between the wires, requiring an insulator. The driver of the tram ortrolleybus must turn off the power when the trolley pole passes through, to prevent arc damage to the insulatorDell Inspiron N7010 battery 5200mAh .
Pantograph equipped locomotives may never run through a section break when one side is de-energized. Of course the locomotive would then become trapped, but as it passes the section break, the pantograph will briefly short the two catenary lines together Dell Inspiron 1464 battery 5200mAh .
If the opposite line is de-energized, this voltage transient may trip supply breakers. If the line is under maintenance, personnel injury may occur as the catenary is suddenly energized. Even if the catenary is properly grounded, the arc generated across the pantograph will likely cause damage to the pantograph, the catenary insulator, or both Dell Inspiron 1564 battery 5200mAh .
Sometimes on a larger electrified railway, tramway or trolleybus system, it is necessary to power different areas of track from different power grids, the synchronisation of the phases of which cannot be guaranteed Dell Inspiron 1764 battery 5200mAh .
(Sometimes the sections are 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 is highly undesirable to connect two unsynchronised grids Dell Inspiron 1320 battery 5200mAh .
A normal section break is insufficient to guard against this, since the pantograph briefly connects both sections.
Instead, a phase break or neutral section 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 Dell Inspiron 1320n battery 5200mAh .
If the two grids are synchronized, this stretch of line is energized (by either supply) and trains run through it normally. If the two supplies are not synchronized, the short isolating section is disconnected from the supplies, leaving it electrically dead, ensuring that the two grids cannot be connected to each other Dell Vostro 1710 battery 5200mAh .
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. When synchronization is lost and the phase break is deenergized, the train's operator must put the controller (throttle) into neutral and coast through an isolated phase break section Dell Vostro 1720 battery 5200mAh .
On the Pennsylvania Railroad, phase breaks were indicated by a position light signal face with all eight radial positions filled by lenses and no center light. When the phase break was active (that is when the catenary sections were out of phase), all lights were lit Dell Studio XPS 1640 battery 5200mAh .
The position light signal aspect was originally devised by the Pennsylvania Railroad but was continued by its successor Amtrak and has been adopted by Metro North. Metal signs were also hung from the catenary supports with the letters PB created by a pattern of drilled holes Dell Vostro A840 battery 5200mAh .
Transnet Freight Rail in South Africa has permanent magnets between the rails at both sides of the neutral section where two phases are separated. These are detected by equipment on the locomotive, which disconnect and reconnect power from the pantographsDell Vostro A860 battery 5200mAh.
A special category of phase break was also developed in American practice, primarily by the Pennsylvania Railroad. Since its traction power network was centrally supplied, and only segmented by abnormal conditions, phase breaks were normally not activeDell Studio 1535 battery 5200mAh/7800mAh .
Phase breaks which were always activated came to be known as Dead Sections. They often were to separate boundaries between power systems (for example, the Hell's Gate Bridge boundary between Amtrak and Metro North's electrification systems), which would never be in-phase Dell Studio 1735 battery 5200mAh/7800mAh .
Since a dead section is, by definition, always dead, no special signal aspect was developed to warn engineers of its presence. A simple metal sign with DS in drilled-hole letters was hung from the catenary supports Dell Vostro 1310 battery 5200mAh .
Trams draw their power from a single overhead wire at about 500 to 750 V, while trolleybuses draw their power from two overhead wires at a similar voltage. Because of that, at least one of the trolleybus wires must be insulated from tram wires Dell Latitude E6400 battery,10400mAh/7800mAh .
This is usually solved 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 wire merges into a solid bar running parallel to the trolleybus wires for about half a metre Dell Latitude E6400 Battery,10400mAh/7800mAh .
Another bar similarly angled at its ends is hung between the trolleybus wires. This is electrically connected above to the tram wire. The tram's pantograph bridges the gap between the different conductors, providing it with a continuous pickup Dell Latitude E6400 Battery,10400mAh/7800mAh .
Where the tram wire crosses, the trolleybus wires are protected by an inverted trough of insulating material extending 20 or 30 mm below.
Until 1946, there was a level crossing in Stockholm, Sweden between the railway south of Stockholm Central Station and a tramway line Dell Latitude E6500 battery,10400mAh/7800mAh .
The tramway operated on 600-700 V DC and the railway on 15 kV AC. Some crossings between tramway/light rail and railways are still extant in Germany. In Zürich, Switzerland the VBZ trolleybus line 32 has a level crossing with the 1,200 V DC railway to mount Uetliberg Dell Latitude E6500 battery,10400mAh/7800mAh ;
at many places in the town, trolleybus lines cross the tramway. In the Swiss village of Suhr, the WSB tramway operating at 1,200 V DC crosses the SBB line at 15 kV AC. In some cities, trolleybuses and trams have shared the same positive (feed) wire. In such cases, a normal trolleybus frog can be used Dell Latitude E6500 battery,10400mAh/7800mAh .
Another system that has been used is to coincide section breaks with the crossing point so that the crossing is electrically dead.
Many cities had trams and trolleybuses both using trolley pole current collection Dell Latitude E6500 battery,10400mAh/7800mAh .
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 auxiliary power.
In Melbourne, Victoria, tram drivers put the controller into neutral and coast through section insulators, indicated by insulator markings between the rails HP Pavilion DV6-1210SA battery - 5200mAh/8800mAh .
Melbourne has four level crossings between electrified suburban railways and tram lines. They have complex switching arrangements to separate the 1,500 V DC overhead of the railway and the 650 V DC of the trams, called an overhead square HP Pavilion DV7 battery - 7200mAh .
Proposals have been put forward which would see these crossings grade separated or the tram routes diverted.
Queensland uses 25 kV AC overhead traction with booster transformers in the Brisbane suburban area and auto transformers elsewhere Ibm THINKPAD X200 Battery 8800mAh .
Western Australia (Perth city) uses 25 kV AC overhead traction with booster transformers.
In Athens, there are two crossings between tram and trolleybus wires, at Vas Ibm THINKPAD X200 Battery 8800mAh .
Amalias Avenue and Vas. Olgas Avenue, and at Ardittou Street and Athanasiou Diakou Street. They use the above-mentioned solution.
From the opening of the tram system in the summer of 2004, trams and trolleybuses in the direction of Pagrati shared the same exclusive lane, about 400m long, on the far right side of Vas Ibm THINKPAD X200 Battery 8800mAh .
Olgas Avenue, with tram and trolleybus wires side-by-side above a narrow lane of road. The trolleybus wires were on the far right of the lane, away from the trams' (very wide) pantographs. Trolleybus drivers were required to drive very slowly because the trolley poles were extended to their limits SONY VAIO VGN-FW21E Battery .
A change of route for trolleybuses was implemented in mid-2005, ending this arrangement.
In Milan, most of the city's tram lines cross its circular trolleybus line once or twice, so crossings between overhead tram and trolleybus wires are quite commonplace Asus M52N Battery .
Trolleybus and tram wires run parallel in some streets, like viale Stelvio and viale Tibaldi.
Multiple overhead lines
There are and were some railways that used two or three overhead lines, usually to carry three-phase current to the trains Dell Latitude E6400 ATG Battery .
Nowadays, three-phase AC current is used only on the Gornergrat Railway and Jungfraujoch 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 SONY VAIO VGN-FW21J Battery.
On these railways, the two conductors of the overhead lines 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 SONY VAIO VGN-FW21L Battery .
These were an experimental railway line of Siemens in Berlin-Lichtenberg in 1898 (length: 1.8 kilometres), the military railway between Marienfelde and Zossen between 1901 and 1904 (length: 23.4 kilometres) and an 800-metre-long section of a coal railway near Cologne, between 1940 and 1949 SONY VAIO VGN-FW21M Battery .
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 SONY VAIO VGN-FW21Z Battery .
All systems of multiple overhead lines have the disadvantage of 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 SONY VAIO VGN-FW25T/B Battery .
The Sihltal Zürich Uetliberg Bahn is the result of a merge of two railways with different electification. To be able to use different electic systems on shared tracks one of the railways (Sihltalbahn) has overhead wire right above the train, and the other line (Uetlibergbahn) has overhead wire a bit off to one side SONY VAIO VGN-FW26T/B Battery .
A catenary is a system of overhead wires used to supply electricity to a locomotive, streetcar, or light rail vehicle which is equipped with a pantograph SONY VAIO VGN-FW27/B Battery .
Unlike simple overhead wires, in which the uninsulated wire or cable is attached by clamps to closely spaced crosswires, themselves supported by line poles, catenary systems use at least two wires. One wire, called the catenary or messenger wire, is hung at a specific tension between line structures SONY VAIO VGN-FW27/W Battery .
A second wire is held in tension by the messenger wire, and is attached to it at frequent intervals by clamps and connecting wires. The second wire is straight and level, parallel to the rail tracks, suspended over it as the roadway of a suspension bridge is over waterSONY VAIO VGN-FW31ZJ Battery .
Simple wire installations are common in light rail applications, especially on city streets, while more expensive catenery systems are especially suited to high-speed operations SONY VAIO VGN-FW27T/H Battery .
The Northeast Corridor in the United States features electrified catenary over a 600-mile or 1000 km distance between Boston, Massachusetts andWashington, D.C., providing power for Amtrak's high-speed Acela Express and other trains SONY VAIO VGN-FW29/B Battery .
Several commuter rail agencies, including MARC, SEPTA, NJ Transit, Metro-North utilize the catenary to provide local service along the Northeast Corridor.
In Cleveland, Ohio the interurban/light rail lines use overhead wires, and the heavy rail line also uses overhead wires, instead of a third rail SONY VAIO VGN-FW290JRB Battery .
This was due to a city ordinance intended to limit air pollution from the large number of steam trains passing through the Cleveland between the east coast and Chicago. Trains switched from steam to overhead catenary electric locomotives at the Collinwood Rail Yards about 10 miles (16 km) east of Downtown Cleveland and similarly at Linndale on the west side SONY VAIO VGN-FW290JTB Battery .
When Cleveland constructed its rapid transit (heavy rail) line between the airport, Downtown Cleveland and beyond it employed similar overhead catenary technologies that the railroads used, and were able to utilize railroad electrification equipment left over after railroads switched from steam to diesel locomotives SONY VAIO VGN-FW290JTH Battery .
Consequently, light and heavy rail public transit systems share trackage for about 3 miles (4.8 km) along theCleveland Hopkins International Airport Red (heavy rail) line, Blue and Green interurban/light rail lines between Cleveland Union Terminal and just past East 55th Street station, where the heavy- and light-rail line tracks separate SONY VAIO VGN-FW33G/E1 Battery .
The Blue Line, running through suburbs northeast of Boston, Massachusetts, uses overhead power lines.
The height of overhead wiring can create hazards at level crossings, where it may be struck by road vehicles SONY VAIO VGN-FW33G/W Battery .
The wiring in most countries is too low to allowdouble stack container trains. The Channel Tunnel has an extended height overhead line to accommodate double-height car and truck transporters. India is proposing a network of freight only lines, which would almost certainly be electrified with extra height wiring and pantographs that can reach it SONY VAIO VGN-FW33GW Battery .
Technical advances lower running costs
The introduction of supercapacitors has promised to drop electrical running costs for trains powered by overhead lines or third rails. Kinetic braking energy is reclaimed by storing electrical energy in supercapacitors onboard the vehicle Dell XPS M1210 Battery) http://www.hdd-shop.co.uk .
This stored energy is used when accelerating the train, when high current is needed. The supplementing supercapacitors reduce current drawn through the electrical supply during acceleration and puts less strain on the distribution system Dell KM958 battery .
Later developments locate banks of supercapacitors at track side. All trains on the system can then use the stored energy in the supercapacitors to supplement the energy drawn through a third rail or overhead wires. Trackside location reduces vehicle weight and creates more onboard space Dell Studio 1555 battery .
However, such locations would require additional equipment to charge the supercapacitors from the overhead line voltage and to generate supplementary power at the voltage and frequency of the overhead line from the stored energy.
Claimed energy reduction is around 30% Sony VGP-BPS13 battery .
Electric railway systems can be more competitive and a real economical alternative to automobiles.
The technology can be used equally well for diesel electric locomotives, where 25% to 40% reduction in energy consumption is claimed, however only onboard location of supercapacitor banks is feasible Sony VGP-BPS13/B battery .
(This technology equally applies to road vehicles that use electric motors for propulsion, such as hybrid cars and buses.) Any electrical equipment that requires regular braking can reduce operating costs using supercapacitors Sony VGP-BPS13/S battery .
Reduced operating costs of elevators on underground railways would be a great benefit to operators and adding to their economic competitiveness.
An additional benefit is that emissions from generating plants and diesel-electric locomotives will be decreased Sony VGP-BPS13A/B battery .
Since 2003, the Mannheim Stadtbahn in Germany has operated a light-rail vehicle using electric double-layer supercapacitors to store braking energy.
A number of companies are developing electric double-layer supercapacitor technology Sony VGP-BPS13B/B battery .
Siemens AG is developing mobile energy storage based on double-layer supercapacitors called Sibac Energy Storage Sitras SES, are developing stationary trackside version. The company Cegelec is also developing an electric double-layer capacitor-based energy storage system Sony VGP-BPL9 battery .
In 1881 the first tram with overhead lines was presented by Werner von Siemens on the International Electric Exposition in Paris 1881 but the installation was removed after that event Sony VGP-BPS13B/B battery .
In October 1883, the first permanent tram service with overhead lines was started on Mödling and Hinterbrühl Tram in Austria. These trams had bipolar overhead lines, consisting of two U-pipes, in which the pantographshung and ran like shuttles Sony VGP-BPL15 battery.
In April to June 1882, Siemens had tested a similar system on his Electromote, an early percursor of the trolleybuses.
Much simpler and more functional was an overhead wire in combination with a pantograph borne by the vehicle and pressed at the line from below Dell Inspiron E1505 battery .
This system, for rail traffic with a unipolar line, was invented by Frank J. Sprague in 1888. Since 1889, it was used at the Richmond Union Passenger Railway in Richmond, Virginia. That was the onset of worldwide use of electric traction HP Pavilion dv6000 Battery.
A railway electrification system supplies electrical energy to railway locomotives and multiple units so that they can operate without having an on-board prime mover. There are several different electrification systems in use throughout the world. Railway electrification has many advantages but requires significant capital expenditure for installation HP Pavilion dv8000 battery .
Characteristics of electric traction
The main advantage of electric traction is a higher power-to-weight ratio than forms of traction such as diesel or steam that generate power on board. Electricity enables faster acceleration and higher tractive effort on steep gradients HP PAVILION DV6000 Battery, 8800mAh .
On locomotives equipped with regenerative brakes, descending gradients require very little use of air brakes as the locomotive's traction motors become generators sending current back into the supply system and/or on-board resistors, which convert the excess energy to heat HP PAVILION DV8000 Battery, 8800mAh .
Other advantages include the lack of exhaust fumes at point of use, less noise and lower maintenance requirements of the traction units. Given sufficient traffic density, electric trains produce fewer carbon emissions than diesel trains, especially in countries where electricity comes primarily from non-fossil sources SONY VAIO VGN-FZ Battery .
A fully electrified railway has no need to switch between methods of traction thereby making operations more efficient. Two countries that approach this ideal are Switzerland and Hong Kong, but both use more than one system HP Pavilion DV6000 battery - 8800mAh ,
so unless multi-system locomotives or other rolling stock is used, a switch of traction method may still be required.
The main disadvantages are the capital cost of the electrification equipment, most significantly for long distance lines which do not generate heavy traffic HP Pavilion DV8000 battery - 7800mAh .
Suburban railways with closely-spaced stations and high traffic density are the most likely to be electrified and main lines carrying heavy and frequent traffic are also electrified in many countries. Also, if the overhead wiring breaks down in some way, all trains can be brought to a standstill HP Pavilion DV6000 battery - 8800mAh .
Electrification systems are classified by three main parameters:
- Direct current (DC)
- Alternating current (AC)
- Frequency HP Pavilion DV8000 battery - 6600mAh
- Contact System
- third rail
- overhead line (catenary) SONY VAIO VGN-FZ18 Battery
Six of the most commonly used voltages have been selected for European and international standardisation. These are independent of the contact system used, so that, for example, 750V DC may be used with either third rail or overhead lines (the latter normally by trams) SONY VAIO VGN-FZ21E Battery .
There are many other voltage systems used for railway electrification systems around the world, and the list of current systems for electric rail traction covers both standard voltage and non-standard voltage systems SONY VAIO VGN-FW31J Battery - 5200mAh/7800mAh/10400mAh .
The permissible range of voltages allowed for the standardised voltages is as stated in standards BS EN 50163 and IEC 60850. These take into account the number of trains drawing current and their distance from the substation SONY VAIO VGN-FW31J Battery - 5200mAh/7800mAh/10400mAh .
Early electric systems used low-voltage DC. Electric motors were fed directly from the traction supply and were controlled using a combination of resistors and relays that connected the motors inparallel or series SONY VAIO VGN-FW21E Battery .
The most common DC voltages are 600 V and 750 V for trams and metros and 1,500 V, 650/750 V third rail for the former Southern Region of the UK and 3 kV overhead. The lower voltages are often used with third or fourth rail systems, whereas voltages above 1 kV are normally limited to overhead wiring for safety reasons SONY VAIO VGN-NR11S/S Battery .
Suburban trains (S-Bahn) lines in Hamburg, Germany, operate using a third rail with 1,200 V, the French SNCF Culoz-Modane line in the Alps used 1,500 V and a third rail until 1976, when a catenary was installed and the third rail was removed SONY VAIO VGN-NR11M/S Battery .
In the UK, south of London, 750 V third rail is used while, for inner London, 650 V is used to allow inter-running with London Underground which uses a 650 V fourth rail system but with the 4th (centre) rail connected to the running rails in inter-running areas SONY VAIO VGN-NR11Z/S Battery .
During the mid-20th century, rotary converters or mercury arc rectifiers were used to convert utility (mains) AC power to the required DC voltage at feeder stations. Today, this is usually done bysemiconductor rectifiers after stepping down the voltage from the utility supply SONY VAIO VGN-NR11Z/T Battery .
The DC system is quite simple but it requires thick cables and short distances between feeder stations because of the high currents required. There are also significant resistive losses. In the United Kingdom, the maximum current that can be drawn by a train is 6,800 A at 750 V Sony VAIO VGN-FZ21E Battery .
The feeder stations require constant monitoring and, on many systems, only one train or locomotive is allowed per section. The distance between two feeder stations at 750 V on third-rail systems is about 2.5 km (1.6 mi). The distance between two feeder stations at 3 kV is about 25 km (16 mi) Sony VAIO VGN-FW21E Battery .
If auxiliary machinery, such as fans and compressors, is powered by motors fed directly from the traction supply, they may be larger because of the extra insulation required for the relatively high operating voltage Sony VAIO VGN-NR11S/S Battery .
Alternatively, they can be powered from a motor-generator set, which offers an alternative way of powering incandescent lights which otherwise would have to be connected as series strings (bulbs designed to operate at traction voltages being particularly inefficient) Sony VAIO VGN-NR11Z/S Battery .
Now solid-state converters (SIVs) and fluorescent lights can be used.
1,500 V DC is used in the Netherlands, Japan, Hong Kong (parts), Ireland, Australia (parts), India (around the Mumbai area alone, to be converted to 25 kV AC like the rest of the country ) Sony VAIO VGN-NR11M/S Battery ,
France, New Zealand (Wellington) and the United States (Chicago area on the Metra Electric district and the South Shore Line interurban line). In Slovakia, there are two narrow-gauge lines in the High Tatras (one a cog railway). In Portugal, it is used in the Cascais Line and, in Denmark, on the suburban S-train system Sony VAIO VGN-NR11Z/T Battery .
In the United Kingdom, 1,500 V DC was used in 1954 for the Woodhead trans-Pennine route (now closed); the system used regenerative braking, allowing for transfer of energy between climbing and descending trains on the steep approaches to the tunnel SONY VAIO VGN-FZ180E Battery .
The system was also used for suburban electrification inEast London and Manchester, now converted to 25 kV AC.
3 kV DC is used in Belgium, Italy, Spain, Poland, the northern Czech Republic, Slovakia, Slovenia, western Croatia, South Africa and former Soviet Unioncountries (also using 25 kV 50 Hz AC) SONY VAIO VGN-FZ220E Battery .
It was also formerly used by the Milwaukee Road's extensive electrification across the Continental Divide and by theDelaware, Lackawanna & Western Railroad (now New Jersey Transit, converted to 25 kV AC) in the United States.
600 V DC is used by Milan's network of tramways and trolleybuses SONY VAIO VGN-FZ340E Battery .
Most electrification systems use overhead wires, but third rail is an option up to about 1,200 V. While use of a third rail does not require the use of DC, in practice, all third-rail systems use DC because it can carry 41% more power than an AC system operating at the same peak voltage SONY VAIO VGN-FZ430E Battery .
Third rail is more compact than overhead wires and can be used in smaller-diameter tunnels, an important factor for subway systems.
Third rail systems can be designed to use top contact, side contact or bottom contact SONY VAIO VGN-FZ460E Battery .
Top contact is less safe, as the live rail is exposed to people treading on the rail unless an insulating hood is provided. Side- and bottom-contact third rail can easily have safety shields incorporated, carried by the rail itself. Uncovered top-contact third rails are vulnerable to disruption caused by ice, snow and fallen leaves SONY VAIO VGN-FZ480E Battery .
DC systems (especially third rail systems) are limited to relatively low voltages and this can limit the size and speed of trains and cannot use low-level platform and also limit the amount of air-conditioning that the trains can provide SONY VAIO VGN-FZ4000 Battery .
This may be a factor favouring overhead wires and high voltage AC, even for urban usage. In practice, the top speed of trains on third-rail systems is limited to 100 mph (160 km/h) because, above that speed, reliable contact between the shoe and the rail cannot be maintained SONY VAIO VGN-FZ31E Battery .
Some road operating trams (streetcars) used conduit third-rail current collection. The third rail was below street level. The tram picked up the current through aplough (U.S. "plow") accessed through a narrow slot in the road SONY VAIO VGN-FZ31B Battery .
In the United States, much (though not all) of the former streetcar system system in Washington, D.C. (discontinued in 1962) was operated in this manner to avoid the unsightly wires and poles associated with electric traction. The same was true with Manhattan's former streetcar system SONY VAIO VGN-FZ31J Battery.
The evidence of this mode of running can still be seen on the track down the slope on the northern access to the abandoned Kingsway Tramway Subway (in central London, United Kingdom), where the slot between the running rails is clearly visible, and on P and Q Streets west of Wisconsin Avenue in the Georgetown neighborhood of Washington DC SONY VAIO VGN-FZ31M Battery ,
where the abandoned tracks have not been paved over. The slot can easily be confused with the similar looking slot for cable trams/cars (indeed, in some cases, the conduit slot was originally a cable slot). The disadvantage of conduit collection included much higher initial installation costs SONY VAIO VGN-FZ31Z Battery ,
higher maintenance costs, and problems with leaves and snow getting in the slot. For this reason, in Washington, D.C. cars on some lines converted to overhead cable on leaving the city center, a worker in a "plow pit" disconnecting the plow while another raised the trolley pole (hitherto hooked down to the roof) to the now-present overhead wire SONY VAIO VGN-FZ38M Battery .
In New York City for the same reasons of cost and operating efficiency outside of Manhattan overhead wire was used. Finally, a new approach to avoiding overhead wires is that taken by the "second generation" tram/streetcar system in Bordeaux, France (entry into service of the first line in December 2003 SONY VGP-BPS8 Battery ;
original system discontinued in 1958)with its APS (alimentation par sol -- ground current feed). This involves a third rail which is not in a slot but runs flush with the surface like the tops of the running rails. The circuit is divided into segments with each segment energized in turn by sensors from the car as it passes over it, the remainder of the third rail remaining "dead" SONY VGP-BPS13/S Battery .
Since each energized segment is completely covered by the lengthy articulated cars, and goes dead before being "uncovered" by the passage of the vehicle, there is no danger to pedestrians. At least initially there were teething troubles in terms of maintaining current feed SONY VGP-BPS13A/B Battery ,
however, and the fact that the system is used exclusively in the historic center, with the cars on leaving this zone converting to conventional overhead pickup, underlines how, esthetics aside, for streetcars/trams it is hard to beat the overhead wire system in terms of overall efficiency SONY VGP-BPS13B/B Battery .
The London Underground in England is one of the few networks that uses a four-rail system. The additional rail carries the electrical return that, on third rail and overhead networks, is provided by the running rails SONY VGP-BPS13A/S Battery .
On the London Underground, a top-contact third rail is beside the track, energized at +420 V DC and a top-contact fourth rail is located centrally between the running rails at ?210 V DC, which combine to provide a traction voltage of 630 V DC SONY VGP-BPS13AS Battery .
The same system was used for Milan's earliest underground line, Milan Metro's line 1, whose more recent lines use an overhead catenary.
This scheme was introduced because of the problems of return currents Dell Inspiron 1320n Battery ,
intended to be carried by the earthed (grounded) running rails, flowing through the iron tunnel linings instead. This can cause electrolytic damage and even arcing if the tunnel segments are not electrically bonded together Dell Studio 1450 Battery .
The problem was exacerbated because the return current also had a tendency to flow through nearby iron pipes forming the water and gas mains. Some of these, particularly Victorian mains that predated London's underground railways, were never constructed to carry currents and had no adequate electrical bonding between pipe segments Dell Studio 1457 Battery .
The four-rail system solves the problem. Although the supply has an artificially created earth point, this connection is derived by using resistors which ensures that stray earth currents are kept to manageable levels Dell Latitude D610 Battery .
London's sub-surface underground railways also operate on the four-rail scheme since, in a number of areas (for example the Piccadilly Line and Metropolitan Line services to Uxbridge), sub-surface and deep-level stock run on the same tracks Toshiba NB100 Battery .
On tracks that London Underground share with National Rail third-rail stock (the Bakerloo and District lines both have such sections), the centre rail is
connected to the running rails, allowing both types of train to operate, at a compromise voltage of 660 V Toshiba Satellite M65 battery .
Underground trains pass straightforwardly from one section to the other at speed; there are specific lineside electrical connections and resistances which separate the two types of supply.
Fourth-rail trains occasionally operate on the National third-rail system Toshiba Satellite M60 battery .
To do so, the centre-rail shoes are bonded to the wheels. This bonding must be removed before operating again on the fourth-rail tracks.
A system proposed (but not used) by the South Eastern and Chatham Railway around 1920 was 1,500 V DC four-rail Dell Latitude D830 Battery .
Technical details are scarce but it is likely that it would have been a mid-earth system with one conductor rail at +750 volts and the other at ?750 volts. This would have facilitated conversion to 750 V DC three-rail at a later date.
A few lines of the Paris Métro in France also operate on a four-rail power scheme but for a very different reason Dell Latitude D620 Battery .
It is not strictly a four-rail scheme as they run on natural rubber tyres running on a pair of narrow roadways made of steel and, in some places, concrete. Since the tyres do not conduct the return current, two conductor rails are provided o
The trains are designed to operate from either polarity of supply, because some lines use reversing loops at one end, causing the train to be reversed during every complete journey (intended to save having to "change ends" by having the operator walk to the other end of the train to make the former last car the lead car in the new direction) Sony VGN-FW11S Battery .
These are overhead electrification systems. Alternating current can be transformed to lower voltages inside the locomotive. This allows much higher voltages and therefore smaller currents along the line, which means smaller energy losses along long railwaysSony VGN-FW11M Battery .
Low-frequency alternating current
Common DC commutating electric motors can also be fed with AC (universal motor), because reversing the current in both stator and rotor does not change the direction of torque Sony VGN-FW139E/H battery .
However, the inductance of the windings made early designs of large motors impractical at standard AC distribution frequencies. In addition, AC induces eddy currents, particularly in non-laminated field pole pieces, that cause overheating and loss of efficiency Dell Latitude E5400 Battery .
In the previous century, five European countries, including Germany, Austria, Switzerland, Norway and Sweden, standardized on 15 kV 16? Hz (one-third of the normal mains frequency) single-phase AC in an attempt to alleviate such problems Dell Latitude E4200 Battery .
On 16 October 1995, Germany, Austria and Switzerland changed the designation from 16? Hz to anominal frequency of 16.7 Hz (though the actual frequency has not changed, its designation has). In the United States (with its 60 Hz distribution system), 25 Hz (an older, now-obsolete standard mains frequency) Dell Inspiron 300M Battery
is used at 11 kV between Washington, D.C. and New York City and between Harrisburg, Pennsylvania and Philadelphia. A 12,500 V 25 Hz section between New York City and New Haven, Connecticut was converted to 60 Hz in the last third of the 20th century Dell Studio 1737 battery .
In the UK, the London, Brighton and South Coast Railway pioneered overhead electrification of its suburban lines in London, London Bridge to Victoria being opened to traffic on 1 December 1909. Victoria to Crystal Palace via Balham and West Norwood opened in May 1911. Peckham Rye to West Norwood opened in June 1912 Dell Inspiron E1505 battery .
Further extensions were not made owing to the First World War. Two lines opened in 1925 under the Southern Railway serving Coulsdon North andSutton railway station. The lines were electrified at 6.7 kV 25 Hz. It was announced in 1926 that all lines were to be converted to DC third rail and the last overhead electric service ran in September 1929 Dell RM791 battery .
In such a system, the traction motors can be fed through a transformer with multiple taps. Changing the taps allows the motor voltage to be changed without requiring power-wasting resistors. Auxiliary machinery is driven by small commutating motors powered from a separate low-voltage winding of the main transformer Toshiba Satellite P10 Battery .
The use of low frequency requires that electricity be converted from utility power by motor-generators or static inverters at the feeding substations, or generated at altogether separate traction powerstations Acer Aspire One battery 10400mAh .
Since 1979, the three-phase induction motor has become almost universally used. It is fed by a static four-quadrant converter which supplies a constant voltage to a pulse-width modulator inverter that supplies the three-phase variable frequency to the motors SONY VGN-FZ210CE Battery .
Polyphase alternating current systems
The majority of the Italian State railway system three-phase system was 3,300 V at 15–16.7 Hz. With such a low frequency, the locomotives did not need gearing Dell Precision M70 Battery .
It is also possible to use the polyphase system regeneratively, as on the Italian State railway's mountain lines, where a loaded train descending could supply much of the power for a train ascending. Experimental polyphase installations in Italy in the 1930s used higher voltage (10 kV) at industrial frequencies (45 or 50 Hz) Toshiba Satellite L305 Battery .
In the United States, the Great Northern Railway's (Cascade Tunnel) first electrified line (1909–1927) was at 6,600 V, 25 Hz.
The main complexity with three-phase systems is the need for three conductors (including the rails), hence two overhead conductorsToshiba Satellite T4900 Battery .
Early locomotives on the Italian State Railways used a wide bow collector which covered both wires but later locomotives used two pantographs side-by-side. In the United States, a pair of trolley poles were used. They worked well with a maximum speed limit of 15 mph Toshiba PA3399U-2BRS battery .
The dual conductor pantograph system is used on four mountain railways that continue to use three phase power (Corcovado Rack Railway in Rio de Janeiro, Brazil, Jungfraubahn and Gornergratbahn in Switzerland and thePetit train de la Rhune in France) Sony VGP-BPS10 battery 5200mAh/7800mAh/10400mAh .
Standard frequency alternating current
Only in the 1950s after development in France (20 kV then 25 kV) and former Soviet Union countries (25 kV) did the standard-frequency single-phase alternating current system become widespread, despite the simplification of a distribution system which could use the existing power supply network Sony VGP-BPS9 battery 5200mAh/7800mAh/10400mAh .
The first attempts to use standard-frequency single-phase AC were made in Hungary since 1923, by the Hungarian Kálmán Kandó on the line between Budapest-Nyugati and Alag, using 16 kV at 50 Hz. The locomotives carried a four-pole rotating phase converter feeding a single traction motor of the polyphase induction type at 600 to 1,100 VSony VGP-BPS11 battery 5200mAh/7800mAh/10400mAh.
The number of poles on the 2,500 hp motor could be changed using slip rings to run at one of four synchronous speeds. The tests were a success so, from 1932 until 1960s, trains on the Budapest-Hegyeshalom line (towards Vienna) regularly used the same systemSony VGP-BPS22 battery 5200mAh/7800mAh/10400mAh .
A few decades after the second world war, the 16 kV was changed to the Russian and later French 25 kV system.
Today, some locomotives in this system use a transformer and rectifier to provide low-voltage pulsating direct current to motorsSony VGP-BPL8 battery 5200mAh/7800mAh/10400mAh .
Speed is controlled by switching winding taps on the transformer. More sophisticated locomotives use thyristor or IGBT circuitry to generate chopped or even variable-frequencyalternating current (AC) that is then supplied to the AC induction traction motors Sony VGP-BPS14 battery 5200mAh/7800mAh/10400mAh .
This system is quite economical but it has its drawbacks: the phases of the external power system are loaded unequally and there is significantelectromagnetic interference generated as well as significant acoustic noise.
A list of the countries using the 25 kV AC 50 Hz single-phase system can be found in the list of current systems for electric rail traction Sony VGP-BPS21 battery 5200mAh/7800mAh/10400mAh .
The United States commonly uses 12.5 and 25 kV at 25 Hz or 60 Hz. 25 kV, 60 Hz AC is the preferred system for new high-speed and long-distance railways, even if the railway uses a different system for existing trains.
To prevent the risk of out-of-phase supplies mixing, sections of line fed from different feeder stations must be kept strictly isolatedToshiba Satellite A200 Battery .
This is achieved by Neutral Sections (also known as Phase Breaks), usually provided at feeder stations and midway between them although, typically, only half are in use at any time, the others being provided to allow a feeder station to be shut down and power provided from adjacent feeder stations Toshiba Satellite 1200 Battery .
Neutral Sections usually consist of an earthed section of wire which is separated from the live wires on either side by insulating material, typically ceramic beads, designed so that the pantograph will smoothly run from one section to the other Toshiba Satellite M300 Battery .
The earthed section prevents an arc being drawn from one live section to the other, as the voltage difference may be higher than the normal system voltage if the live sections are on different phases and the protective circuit breakers may not be able to safely interrupt the considerable current that would flow SONY VGP-BPS13A/Q Battery .
To prevent the risk of an arc being drawn across from one section of wire to earth, when passing through the neutral section, the train must be coasting and the circuit breakers must be open. In many cases, this is done manually by the driver. To help them, a warning board is provided just before both the neutral section and an advanced warning some distance before SONY VGP-BPS13A/Q Battery .
A further board is then provided after the neutral section to tell the driver to re-close the circuit breaker, although the driver must not do this until the rear pantograph has passed this board. In the UK, a system known as Automatic Power Control (APC) automatically opens and closes the circuit breaker SONY VGP-BPS13B/Q Battery ,
this being achieved by using sets of permanent magnets alongside the track communicating with a detector on the train. The only action needed by the driver is to shut off power and coast and therefore warning boards are still provided at and on the approach to neutral sections SONY VGP-BPS13B/Q Battery .
On French high-speed rail lines, the UK High Speed 1 Channel Tunnel rail link and in the Channel Tunnel itself, neutral sections are negotiated automatically.
In 2006, 240,000 km (25% by length) of the world rail network was electrified and 50% of all rail transport was carried by electric traction SONY VGP-BPS13/Q Battery .
- lower running cost of locomotives and multiple units
- lower maintenance cost of locomotives and multiple units
- higher power-to-weight ratio, resulting in SONY VGP-BPS13/Q Battery
- fewer locomotives
- faster acceleration
- higher practical limit of power
- higher limit of speed SONY VGP-BPS21A/B Battery
- less noise pollution (quieter operation)
- reduced power loss at higher altitudes (for power loss see Diesel engine)
- lack of dependence on crude oil as fuel
- less environmental pollution, even if electricity is produced by fossil fuels SONY VGP-BPS21/S Battery
- upgrading brings significant cost,
- especially where tunnels and bridges and other obstructions have to be altered for clearance SONY VGP-BPS21B Battery
- alterations or upgrades will be needed on the railway signalling to take advantage of the new traffic characteristics
Trade-offs include: SONY VGP-BPS21A Battery
- Maintenance costs of the lines may be increased, but many systems claim lower costs due to reduced wear-and-tear from lighter rolling stock.There are additional maintenance costs associated with the electrical equipment but, if there is sufficient traffic, reduced track and engine maintenance costs can exceed the costs of this maintenance SONY VGP-BPS21 Battery .
- Network effects are a large factor with electrification. When converting lines to electric, the connections with other lines must be considered. Some electrifications have eventually been removed because of the through traffic to non-electrified lines Sony VGP-BPS21A/B Battery .
- If through traffic is to have any benefit, time consuming engine switches must occur to make such connections or expensive dual mode engines must be used. This is mostly an issue for long distance trips, but many lines come to be dominated by through traffic from long-haul freight trains Sony VGP-BPS21/S Battery
- (usually running coal, ore, or containers to or from ports). In theory, these trains could enjoy dramatic savings through electrification, but it can be too costly to extend electrification to isolated areas, and unless an entire network is electrified, companies often find that they need to continue use of diesel trains even if sections are electrified Sony VGP-BPS21A Battery .
- The increasing demand for container traffic which is more efficient when utilizing the double-stack car also has network effect issues with existing electrifications due to insufficient clearance of overhead electrical lines for these trains, but electrification can be built or modified to have sufficient clearance, at additional cost Sony VGP-BPS21 Battery .
Additionally, there are issues of connections between different electrical services, particularly connecting intercity lines with sections electrified for commuter traffic, but also between commuter lines built to different standards Sony Vaio PCG-5G2L Battery .
This can cause electrification of certain connections to be very expensive simply because of the implications on the sections it is connecting. Many lines have come to be overlaid with multiple electrification standards for different trains to avoid having to replace the existing rolling stock on those lines Sony Vaio PCG-5G3L Battery .
Obviously, this requires that the economics of a particular connection must be more compelling and this has prevented complete electrification of many lines. In a few cases, there are diesel trains running along completely electrified routes and this can be due to incompatibility of electrification standards along the route Sony Vaio PCG-5J1L Battery .
Summary of advantages and disadvantages:
- Lines with low frequency of traffic may not be feasible for electrification (especially using regenerative braking), because lower running cost of trains may be overcome by the higher costs of maintenance Sony Vaio PCG-5K2L Battery .
- Therefore most long-distance lines in North America and many developing countries are not electrified due to relatively low frequency of trains.
- Electric locomotives may easily be constructed with greater power output than most diesel locomotives Sony Vaio PCG-5J2L Battery .
- For passenger operation it is possible to provide enough power with diesel engines (see e.g. 'ICE TD') but, at higher speeds, this proves costly and impractical. Therefore, almost all high speed trains are electric.
- The high power of electric locomotives gives them the ability to pull freight at higher speed over gradients Sony Vaio PCG-5K1L Battery ;
- in mixed traffic conditions this increases capacity when the time between trains can be decreased. The higher power of electric locomotives and an electrification can also be a cheaper alternative to a new and less steep railway if trains weights are to be increased on a system Sony Vaio PCG-6S2L Battery .
There is a significant amount of published material that concludes that electric trains are more energy efficient than diesel-powered trains and, with suitable energy production, can have a smallercarbon dioxide footprint. Some of the reasons include Sony Vaio PCG-6S3L Battery :
- electric trains are generally lighter than self powered versions (eg diesel traction);
- they do not have to carry the weight of prime movers, transmission and fuel Sony Vaio PCG-6V1L Battery .
- this is partially offset, however, by the weight of electrical control equipment, and in the case with high-voltage AC by the weight of traction transformers, which may be particularly heavy with low frequency AC (e.g. 16.7 Hz.) Sony Vaio PCG-6W1L Battery .
- the electricity may be generated from various energy sources which are more efficient than a diesel engine, as well as lessening reliance on petroleum products and reducing carbon dioxide emissions, including Sony Vaio PCG-6W2L Battery ;
- nuclear power,
- renewable resources (e.g. hydroelectricity, wind generation, etc.),
- large fossil fuel using power stations with greater efficiency (although they may still have a relatively large carbon footprint). Sony Vaio PCG-6W3L Battery
- under certain conditions, some suitably equipped electric trains can use regenerative braking to return power to the electrification system so that it may be used elsewhere;
- by other vehicles within the network section Sony Vaio PCG-7111L Battery ;
- often implemented in tram networks, where there is a high density of vehicles in each fairly short powered section,
- on high voltage mainlines where there may be several trains within each long section Sony Vaio PCG-7112L Battery ,
- on mountainous lines where trains may be scheduled such that one is ascending whilst another descends;
- in some form of energy storage, such as flywheel energy storage so that it may be used later (eg to accelerate a train from a station at which it has recently stopped) Sony Vaio PCG-7113L Battery
- some systems, such as most 25 kV AC systems in the UK, are able to return excess energy to the public network.
- by other vehicles within the network section Sony Vaio PCG-7111L Battery ;
According to widely accepted global energy reserve statistics , the reserves of liquid fuel are much less than gas and coal (at 42, 167 and 416 years respectively) Sony Vaio PCG-7133L Battery .
Most countries with large rail networks do not have significant oil reserves and those that did, like the United States and Britain, have exhausted much of their reserves and have suffered declining oil output for decades. Therefore, there is also a strong economic incentive to substitute oil for other fuels Sony Vaio PCG-7Z2L Battery .
Rail electrification is often considered an important route towards consumption pattern reform.
The external cost of railway is lower than other modes of transport but the electrification brings it down further if it is sustainableSony Vaio PCG-8Y1L Battery .
Also, the lower cost of energy from well to wheel and the ability to reduce pollution and greenhouse gas in the atmosphere according to the Kyoto Protocol is an advantage.
Research and development
Another result of electrification is the effect on locomotive and wagon productivity and it is going to be more effective by more railway research in this field Sony Vaio PCG-8Y2L Battery .
The trend of technology in railway electrification is very important to adopt the efforts for better results, for example the trend from GTO (Gate turn-off thyristor) to IGBT (Insulated-gate bipolar transistor) for more powerful locomotives with higher reliability is one of the elements of Technology roadmap (TRM) Sony Vaio PCG-8Z1L Battery
and the loop to have a mature system as in Maturity road mapping with the Technology transfer provision.
Volk's Electric Railway (VER) is the oldest operating electric railway in the world.It is a narrow gauge railway that runs along a length of the seafront of the English seaside resort of Brighton Sony Vaio PCG-8Z2L Battery .
It was built by Magnus Volk, the first section being completed in August 1883.
oday the line runs between terminal stations at Aquarium (a short distance from the Palace Pier) and Black Rock (at Black Rock, not far from Brighton Marina), with an intermediate station and depot at Paston Place SONY VAIO VGN-FW31J Battery .
The line has a gauge of 2 ft 8 1?2 in (825 mm), It is electrified at 160 V DC using a third rail, and is just under 11?4 miles (2 km) long.
Operated as a historical seafront tourist attraction, the railway does not usually run during the winter months, and its service is also occasionally liable to suspension due to severe weather or maintenance issues SONY VAIO VGN-FW31E Battery .
Information on any current service changes is available from the railway office.
A model of a yellow Volks carriage in on show in the foyer of the Brighton Toy and Model Museum SONY VAIO VGN-FW31B Battery .
The initial 1883 line was intended as a temporary summer attraction and ran for only 1?4 miles (402 m) between Swimming Arch(opposite the main entrance to Brighton Aquarium, and adjacent to the site of the future Palace Pier) and Chain Pier SONY VAIO VGN-FW31M Battery .
It was built to a gauge of 2 ft (610 mm) and electrical power at 50 V DC was supplied to the cars using the two running rails . In 1884 the line was extended from Chain Pier to Paston Place, the gauge widened to2 ft 9 in (838 mm), and the electrical supply increased to 160 V DC SONY VAIO VGN-FW31Z Battery .
In 1886 a third rail was added to avoid power loss along the extended line, and the gauge tightened to its current 2 ft 8 1?2in (825 mm).
In 1896 the unusual Brighton and Rottingdean Seashore Electric Railway was built by Volk SONY VAIO VGN-FW38M Battery .
This was unsuccessful and closed in 1901, when the Volk's Electric Railway was extended from Paston Place to Black Rock. Paston Place was also the home of Volk's Seaplane Station, which was used by Volk's son George Herbert Volk SONY VAIO VGN-AW41JF Battery .
In 1930 the line was cut back 200 yards (183 m) from Palace Pier to its present terminus, still known as Aquarium, and in 1937 the Black Rock end was also shortened by around 200 yards (183 m). (In 1935 a lido had been built at Black Rock.) SONY VAIO VGN-AW41JF/H Battery
In 1940 the Brighton Corporation took control of the line. It was closed during World War II, but reopened in 1948. Winter operation ceased from 1954, although the line did reopen temporarily in the winter of 1980 to cash in on the large numbers of sightseers who had come to look at the Athina B, a freighter that had beached near the Palace Pier SONY VAIO VGN-AW41MF Battery .
2-car multiple operation was introduced in 1964. In recent years there has been a decline in visitor numbers due topackage holidays. In 1995 the Volk's Electric Railway Association was formed to help preserve the line SONY VAIO VGN-AW41MF/H Battery .
In the late 1990s the Black Rock end of the line was again shortened by a 100 yards (91 m) or so to permit a storm water storage scheme to be built in the marina area, the new station retaining the name of the original SONY VAIO VGN-FW30B Battery .
The single platform station, which shares a building with a new Southern Water pumping station, opened in 1998 and is not quite centred with the ornamental terraces above and behind it, causing the view of the area (from out at sea) to be asymmetrical SONY VAIO VGN-FW50B Battery .
The line speed of the railway is low enough that it is essentially operated as a tramway. There is a passing place at Half Way station. There is a further passing place roughly midway between Half Way and Black Rock though it is rarely used as such SONY VAIO VGN-FW51B/W Battery .
Usually two trains operate from end to end, passing at Half Way station. In general, there is only one train on each single track at any one time. However, in busy periods the railway is permitted to operate with two trains on one single track section with one train following almost immediately behind the other SONY VAIO VGN-FW51MF Battery .
There are warning lights at pedestrian crossing points to the beach with a warbling siren to warn of the approach of a train. A following train is required to signal its approach to a pedestrian crossing point by sounding its klaxon horn SONY VAIO VGN-FW51MF/H Battery .
In wave theory, a phased array is a group of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions. SONY VAIO VGN-FW51ZF Battery .
Phased array transmission was originally developed in 1905 by Nobel Laureate Karl Ferdinand Braun who demonstrated enhanced transmission of radio waves in one direction. DuringWorld War II, Nobel Laureate Luis Alvarez used phased array transmission in a rapidly-steerable radar system for "ground-controlled approach" SONY VAIO VGN-FW51ZF/H Battery .
a system to aid in the landing of aeroplanes in England. At the same time GEMA in Germany built the PESA Mammut 1. It was later adapted for radio astronomyleading to Nobel Prizes for Physics for Antony Hewish and Martin Ryle after several large phased arrays were developed at the University of Cambridge SONY VAIO VGN-FW52JB Battery .
The design is also used in radar, and is generalized in interferometric radio antennas. In 2007 DARPA researchers announced a 16 element phased array integrated with all necessary circuits to send at 30–50 GHz on a single silicon chip for military purposes SONY VAIO VGN-FW54FB Battery .
An antenna array is a multiple of active antennas coupled to a common source or load to produce a directive radiation pattern. Usually the spatial relationship also contributes to the directivity of the antenna SONY VAIO VGN-FW70DB Battery .
Use of the term "active antennas" is intended to describe elements whose energy output is modified due to the presence of a source of energy in the element (other than the mere signal energy which passes through the circuit) or an element in which the energy output from a source of energy is controlled by the signal input SONY VAIO VGN-FW71DB/W Battery .
One common application of this is with a standard multiband television antenna, which has multiple elements coupled together.
The relative amplitudes of — and constructive and destructive interference effects among — the signals radiated by the individual antennas determine the effective radiation pattern of the array SONY VAIO VGN-FW72JGB Battery .
A phased array may be used to point a fixed radiation pattern, or to scan rapidly in azimuth or elevation. Simultaneous electrical scanning in both azimuth and elevation was first demonstrated in a phased array antenna at Hughes Aircraft Company, Culver City, CA, in 1957 (see Joseph Spradley SONY VAIO VGN-FW73JGB Battery .
, “A Volumetric Electrically Scanned Two-Dimensional Microwave Antenna Array,” IRE National Convention Record, Part I - Antennas and Propagation; Microwaves, New York: The Institute of Radio Engineers, 1958, 204-212). When phased arrays are used in sonar, it is called beamforming SONY VAIO VGN-FW74FB Battery .
The phased array is used for instance in optical communication as a wavelength-selective splitter.
For information about active as well as passive phased array radars, see also active electronically scanned array SONY VAIO VGN-FW81HS Battery .
In broadcast engineering, phased arrays are required to be used by many AM broadcast radio stations to enhance signal strength and therefore coverage in the city of license, while minimizing interference to other areas SONY VAIO VGN-FW81NS Battery .
Due to the differences between daytime and nighttime ionospheric propagation atmediumwave frequencies, it is common for AM broadcast stations to change between day (groundwave) and night (skywave) radiation patterns by switching the phase and power levels supplied to the individual antenna elements (mast radiators) daily at sunrise and sunset SONY VAIO VGN-FW81S Battery .
More modest phased array longwire antenna systems may be employed by private radio enthusiasts to receive longwave, mediumwave (AM) and shortwave radio broadcasts from great distances SONY VAIO VGN-FW82DS Battery .
On VHF, phased arrays are used extensively for FM broadcasting. These greatly increase the antenna gain, magnifying the emitted RF energy toward thehorizon, which in turn greatly increases a station's broadcast range. In these situations, the distance to each element from the transmitter is identical, or is one (or other integer) wavelength apart. SONY VAIO VGN-FW82JS Battery .
Phasing the array such that the lower elements are slightly delayed (by making the distance to them longer) causes a downward beam tilt, which is very useful if the antenna is quite high on a radio tower SONY VAIO VGN-FW82XS Battery .
Other phasing adjustments can increase the downward radiation in the far field without tilting the main lobe, creating null fill to compensate for extremely highmountaintop locations, or decrease it in the near field, to prevent excessive exposure to those workers or even nearby homeowners on the ground SONY VAIO VGN-FW83DS Battery ..
The latter effect is also achieved by half-wave spacing – inserting additional elements halfway between existing elements with full-wave spacing. This phasing achieves roughly the same horizontal gain as the full-wave spacing; that is, a five-element full-wave-spaced array equals a nine- or ten-element half-wave-spaced array SONY VAIO VGN-FW83JS Battery .
Phased array radar systems are also used by warships of many navies. Phased array radars allow a warship to use one radar system for surface detection and tracking (finding ships), air detection and tracking (finding aircraft and missiles) and missile uplink capabilities SONY VAIO VGN-FW83XS Battery .
Prior to using these systems, eachsurface-to-air missile in flight required a dedicated fire-control radar, which meant that ships could only engage a small number of simultaneous targets. Phased array systems can be used to control missiles during the mid-course phase of the missile's flight SONY VAIO VGN-FW90NS Battery .
During the terminal portion of the flight, continuous-wave fire control directors provide the final guidance to the target. Because the radar beam is electronically steered, phased array systems can direct radar beams fast enough to maintain a fire control quality track on many targets simultaneously while also controlling several in-flight missiles SONY VAIO VGN-FW37J/B Battery .
The AN/SPY-1 phased array radar, part of the Aegis combat system deployed on modern U.S. cruisers and destroyers, "is able to perform search, track and missile guidance functions simultaneously with a capability of over 100 targets." Likewise SONY VAIO VGN-FW37J Battery ,
the Thales Herakles phased array multi-function radar onboard the Formidable class frigates of the Republic of Singapore Navy has a track capacity of 200 targets and is able to achieve automatic target detection, confirmation and track initiation in a single scanSONY VAIO VGN-FW378J/B Battery ,
while simultaneously providing mid-course guidance updates to the MBDA Aster missiles launched from the ship. The German Navy and the Dutch Navy have developed the Active Phased Array RadarSystem (APAR).
There are two main different types of phased arrays, also called beamformers SONY VAIO VGN-FW378DH Battery .
There are time domain beamformers and frequency domain beamformers.
A time domain beamformer works, as the name says, by doing time-based operations. The basic operation is called "delay and sum"SONY VAIO VGN-FW378J/B Battery .
It delays the incoming signal from each array element by a certain amount of time, and then adds them together. Sometimes a multiplication with a window across the array is done to increase the mainlobe/sidelobe ratio, and to insert zeroes in the characteristic SONY VAIO VGN-FW37J Battery .
There are two different types of frequency domain beamformers. The first type separates the different frequency components that are present in the received signal into different frequency bins (using either an FFT or a filterbank). When different delay and sum beamformers are applied to each frequency bin SONY VAIO VGN-FW41E/H Battery ,
it is possible to point the main lobe to different directions for different frequencies. This can be an advantage for communication links.
The other type of frequency domain beamformers makes use of so called Spatial Frequency SONY VAIO VGN-FW41J/H Battery .
This means that an FFT is taken across the different array elements, not in time. The output of the N point FFT are N channels, which are evenly divided in space. This approach makes a simple implementation of several beamformers at the same time possible, but this approach is not flexible, because the different directions are fixed SONY VAIO VGN-FW41M/H Battery SONY VAIO VGN-FWZJ/H Battery .