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An electric locomotive is a locomotive powered by electricity from an external source. Sources include overhead lines, third rail, or an on-board electricity storage device such as a battery or flywheel system.

Electrically propelled locomotives with on-board fueled prime mover, such as diesel engines or gas turbines, are classed as diesel-electric or gas turbine electric locomotives because the electric generator/motor combination only serves as a power transmission system.


One advantage of electrification is the lack of pollution from the locomotives themselves. Electrification also results in higher performance, lower maintenance costs, and lower energy costs for electric locomotives.

Power plants, even if they burn fossil fuels, are far cleaner than mobile sources such as locomotive engines. Also the power for electric locomotives can come from clean and/or renewable sources, including geothermal power, hydroelectric power, nuclear power, solar power, and wind turbines. Electric locomotives are also quiet compared to diesel locomotives since there is no engine and exhaust noise and less mechanical noise. The lack of reciprocating parts means that electric locomotives are easier on the track, reducing track maintenance.

Power plant capacity is far greater than what any individual locomotive uses, so electric locomotives can have a higher power output than diesel locomotives and they can produce even higher short-term surge power for fast acceleration. Electric locomotives are ideal for commuter rail service with frequent stops. They are used on all high-speed lines, such as ICE in Germany, Acela in the US, Shinkansen in Japan and TGV in France. Electric locomotives are also used on freight routes that have a consistently high traffic volume, or in areas with advanced rail networks.

Electric locomotives benefit from the high efficiency of electric motors, often above 90%. Additional efficiency can be gained from regenerative braking, which allows kinetic energy to be recovered during braking to put some power back on the line. Newer electric locomotives use AC motor-inverter drive systems that provide for regenerative braking.

The chief disadvantage of electrification is the cost for infrastructure (overhead power lines or electrified third rail, substations, control systems). Public policy in the US currently interferes with electrification—higher property taxes are imposed on privately owned rail facilities if they have electrification facilities. Also, US regulations on diesel locomotives are very weak compared to regulations on automobile emissions or power plant emissions.

In Europe and elsewhere, railroad networks are considered part of the national transport infrastructure, just like roads, highways and waterways, and therefore are financed by the state. Operators of the rolling stock pay fees according to rail use. This makes possible the large investments required for the technically, and in the long-term also, economically advantageous electrification. Because railroad infrastructure is privately owned in the US, railroads are unwilling to make the necessary investments for electrification.


The first known electric locomotive was built by a Scotsmanmarker, Robert Davidson of Aberdeenmarker in 1837 and was powered by galvanic cells ('batteries'). Davidson later built a larger locomotive named Galvani which was exhibited at the Royal Scottish Society of Arts Exhibition in 1841. It was tested on the Edinburgh and Glasgow Railway in September of the following year, but the limited electric power available from batteries prevented its general use.The first electric passenger train was presented by Werner von Siemens at Berlinmarker in 1879. The locomotive was driven by a 2.2 kW motor and the train which consisted of the locomotive and three cars reached a maximum speed of 13 km/h.During four months the train carried 90,000 passengers on a 300 meter long circular track. The electricity was supplied through a third isolated rail situated between the tracks.A stationary dynamo nearby provided the electricity.The world's first electric tram line opened in Lichterfelde near Berlin, Germany, in 1881. It was built by Werner von Siemens (see Berlin Straßenbahn).In the US, electric trolleys were pioneered in 1888 on the Richmond Union Passenger Railway, using equipment designed by Frank J. Sprague.

Much of the early development of electric locomotion was driven by the increasing use of tunnels, particularly in urban areas. Smoke from steam locomotives was noxious, and municipalities were increasingly inclined to prohibit their use within their limits. Thus the first successful working, the City and South London Railway underground line in the UK, was prompted by a clause in its enabling act prohibiting use of steam power. This line opened in 1890, using electric locomotives built by Mather and Platt. Electricity quickly became the power supply of choice for subways, abetted by the Sprague's invention of multiple-unit train control in 1897. Surface and elevated rapid transit systems generally used steam until forced to convert by ordinance.

In 1894, the Hungarianmarker engineer Kálmán Kandó developed high-voltage three phase alternating current motors and generators for electric locomotives; he is known as "the father of the electric train". His work on railway electrification was done at the Ganz electric works in Budapestmarker. He was the first who recognised that an electric train system can only be successful if it can use the electricity from public networks. After realising that, he also provided the means to build such a rail network by inventing a rotary phase converter suitable for locomotive usage.

The first use of electrification on a mainline was on a four-mile stretch of the Baltimore Belt Linemarker of the Baltimore and Ohio Railroad (B&O) in 1895. This track connected the main portion of the B&O to the newly built line to New York, and it required a series of tunnels around the edges of Baltimore's downtown. Parallel tracks on the Pennsylvania Railroad had shown that coal smoke from steam locomotives would be a major operating issue, as well as a public nuisance. Three Bo+Bo units were initially used, at the south end of the electrified section; they coupled onto the entire train, locomotive and all, and pulled it through the tunnels.

In Europe, electrification projects initially focused on mountainous regions for several reasons: coal supplies were difficult and hydroelectric power was readily available; and electric locomotives gave more traction on steeper lines. For example; today 100% of Swiss lines are electrified.

Railroad entrances to New York Citymarker required similar tunnels, and the smoke problems were more acute there. A collision in the Park Avenue tunnel in 1902 led the New York State legislature to outlaw the use of smoke-generating locomotives south of the Harlem Rivermarker after July 1, 1908. In response, electric locomotives began operation in 1904 on the New York Central Railroad. In the 1930s the Pennsylvania Railroad, which also had introduced electric locomotives because of the NYC regulation, electrified its entire territory east of Harrisburg, Pennsylvaniamarker.

Italian railways were the first in the world to introduce electric traction (designed by Kálmán Kandó at the Ganz electric works, Budapest) for the entire length of a mainline rather than just a short stretch. During the period of electrification, some tests were made as to which type of power supply to use: in some sections there was a 3.6kV 16.6Hz three-phase power supply, in others there was 1.5kVdc, 3kVdc and 10kVac 50Hz supply. During the fascist period, 3kVdc power was chosen for the entire Italian railway system. (Actually, 1500Vdc is now only in use near France; 25kV 50Hz is used on high speed trains, and the rest of the system uses 3kVdc).

In the United States, the Chicago, Milwaukee, St. Paul and Pacific Railroad (the Milwaukee Road), the last transcontinental line to be built, electrified its lines across the Rocky Mountains and to the Pacific Ocean starting in 1915. A few East Coast lines, notably the Virginian Railway and the Norfolk and Western Railway, found it expedient to electrify short sections of their mountain crossings. However, by this point, electrification in the United States was more associated with dense urban traffic, and the center of development shifted to Europe, where electrification was widespread.

In 1923, the first electric locomotive with a phase converter was constructed on the basis of Kandó’s designs in Hungarymarker, and serial production began soon after. The section of the Hungarian State Railways between Budapest - Hegyeshalom - Vienna (1929) was built based on Kandó’s invention.

The 1960s saw the electrification of many European main lines (Eastern Europe included) European electric locomotives technology had improved steadily from the 1920s onwards. By comparison, the Milwaukee Road class EP-2 (1918) weighed 240 t, with a power of 3,330 kW and a maximum speed of 112 km/h; in 1935, German E 18 had a power of 2,800 kW, but weighed only 108 tons and had a maximum speed of 150 km/h. On March 29 1955 French locomotive CC 7107 reached a speed of 331 km/h. In 1960 the SJ Class Dm 3 locomotives introduced on the Swedish Railways produced a record 7,200 kW. Locomotives capable of commercial passenger service at 200 km/h appeared in Germany and France in the same period. Further improvements resulted from the introduction of electronic control systems, which permitted the use of increasingly lighter and more powerful motors (standardising from the 1990s onwards on asynchronous three-phase motors, fed through GTO-inverters).

In the United States, the use of electric locomotives declined in the face of dieselization. Diesels shared some of the electric locomotive’s advantages of over steam, and the cost of building and maintaining the power supply infrastructure, which had always worked to discourage new installations, brought on the elimination of most mainline electrification outside the Northeast. Except for a few captive systems (e.g. the Black Mesa and Lake Powell), by 2000 electrification was confined to the Northeast Corridor and some commuter service; even there, freight service was handled by diesels.

In the 1980s, development of very high-speed service brought a revival of electrification. The Japanese Shinkansen and the French TGV were the first systems for which devoted high-speed lines were built from scratch. Similar programs were undertaken in Italymarker, Germanymarker and Spainmarker; in the United States the only new mainline service was an extension of electrification over the Northeast Corridor from New Haven, Connecticutmarker to Boston, Massachusettsmarker, though new light rail systems, using electrically powered cars, continued to be built.

On 2 September 2006 a standard production Siemens Electric locomotive of the Eurosprinter type ES64-U4 (ÖBB Class 1216) achieved a speed of 357 km/h, the record for a locomotive-hauled train, on the new line between Ingolstadt and Nuremberg.

Electric locomotive types

The operating controls of the gauge cogwheel electric locomotive BDeh 4/4 view, operating in line Luzern-Engelberg.
The wheel controls motor power, not driving direction.

An electric locomotive can be supplied with power from

This is in marked contrast to a diesel-electric locomotive, which combines an onboard diesel engine with an electrical power transmission or store (battery, ultracapacitor) system.

The distinguishing design features of electric locomotives are:
  • The type of electrical power used, either alternating current or direct current.
  • The method for store (batteries, ultracapacitors) or collecting (transmission) electrical power.
  • The means used to mechanically couple the traction motors to the driving wheels (drivers).

Direct or alternating current

The most fundamental difference lies in the choice of direct (DC) or alternating current (AC). The earliest systems used direct current as, initially, alternating current was not well understood and insulation material for high voltage lines was not available. Direct current locomotives typically run at relatively low voltage (600 to 3,000 volts); the equipment is therefore relatively massive because the currents involved are large in order to transmit sufficient power. Power must be supplied at frequent intervals as the high currents result in large transmission system losses.

As alternating current motors were developed, they became the predominant types, particularly on longer routes. High voltages (tens of thousands of volts) are used because this allows the use of low currents; transmission losses are proportional to the square of the current (e.g. twice the current means four times the loss). Thus, high power can be conducted over long distances on lighter and cheaper wires. Transformers in the locomotives transform this power to a low voltage and high current for the motors.A similar high voltage, low current system could not be employed with direct current locomotives because there is no easy way for DC to do the voltage/current transformation so efficiently achieved by AC transformers.

AC traction uses seldom two-phase lines in place ot single phase lines. The transmitted three-phase current drives induction motors, which do not have sensitive commutators and permit easy realisation of a regenerative brake. Speed control is made by changing the number of pole pairs in the stator circuit and by switching additional resistors in the rotor circuit. The two-phase lines are heavy and complicated near switches, where the phases have to cross each other. The system was used in large style in the northern part of Italy till 1976 and is still in use on some rack railways in Switzerland. The simple feasibility of a fail safe electric brake is an advantage of the system, while the speed control and the two-phase lines are problematic.

The previous direct commutators had problems at both start and low velocities. Rectifier locomotives, which used AC power transmission and DC motors, were common. Today's advanced electric locomotives have invariably brushless three-phase AC induction motors. These polyphase machines are powered from GTO-, IGCT- or IGBT-based inverters. The cost of electronic devices in a modern locomotive can be up to 50% of the total cost of the vehicle.

Electric traction allows the use of regenerative braking, in which the motors are used as brakes and become generators that transform the motion of the train into electrical power that is then fed back into the lines. This system is particularly advantageous in mountainous operations, as descending locomotives can produce a large portion of the power required for ascending trains.

Most systems have a characteristic voltage, and in the case of AC power a system frequency. Many locomotives over the years were equipped to handle multiple voltages and frequencies as systems came to overlap or were upgraded. American FL9 locomotives were equipped to handle power from two different electrical systems and could also operate as a conventional diesel-electric.

While recently designed systems invariably operate on alternating current, many existing direct current systems are still in use – e.g. in South Africa, and the United Kingdommarker (750 V and 1,500 V); Netherlandsmarker, Japanmarker, Mumbaimarker, Irelandmarker (1,500 V); Sloveniamarker, Belgiummarker, Italymarker, Polandmarker, Russiamarker, Spainmarker (3,000 V), and the cities of Washington DCmarker (750 V).

Power transmission

Electrical circuits require two connections (or for three phase AC, three connections). From the very beginning the trackwork itself was used for one side of the circuit. Unlike model railroads, however, the trackwork normally supplies only one side, the other side(s) of the circuit being provided separately.

The original Baltimore and Ohio Railroad electrification used a sliding shoe in an overhead channel, a system quickly found to be unsatisfactory. It was replaced with a third rail system, in which a pickup (the "shoe") rode underneath or on top of a smaller rail parallel to the main track, somewhat above ground level. There were multiple pickups on both sides of the locomotive in order to accommodate the breaks in the third rail required by trackwork. This system is preferred in subway because of the close clearances it affords.

However, railways generally tend to prefer overhead lines, often called "catenaries" after the support system used to hold the wire parallel to the ground. Three collection methods are possible:

  • Trolley pole: a long flexible pole, which engages the line with a wheel or shoe.
  • Bow collector: a frame that holds a long collecting rod against the wire.
  • Pantograph: a hinged frame that holds the collecting shoes against the wire in a fixed geometry.

Of the three, the pantograph method is best suited for high-speed operation. Some locomotives are equipped to use both overhead and third rail collection(e.g. British Rail Class 92).

Driving the wheels

During the initial development of railroad electrical propulsion, a number of drive systems were devised to couple the output of the traction motors to the wheels. Early locomotives used often jackshaft drives. In this arrangement, the traction motor is mounted within the body of the locomotive and drives the jackshaft through a set of gears. This system was employed because the first traction motors were too large and heavy to mount directly on the axles. Due to the number of mechanical parts involved, frequent maintenance was necessary. The jackshaft drive was abandoned for all but the smallest units when smaller and lighter motors were developed,

Several other systems were devised as the electric locomotive matured. The Buchli drive was a fully-spring loaded system, in which the weight of the driving motors was completely disconnected from the driving wheels. First used in electric locomotives from the 1920s, the Buchli drive was mainly used by the French SNCF and Swiss Federal Railways. The quill drive was also developed about this time, and mounted the traction motor above or to the side of the axle and coupled to the axle through a reduction gear and a semi-flexible hollow shaft - the quill. The Pennsylvania Railroad GG1 locomotive used a quill drive. Again, as traction motors continued to shrink in size and weight, quill drives gradually fell out of favour.

Another drive example was the "bi-polar" system, in which the motor armature was the axle itself, the frame and field assembly of the motor being attached to the truck (bogie) in a fixed position. The motor had two field poles, which allowed a limited amount of vertical movement of the armature. This system was of limited value since the power output of each motor was limited. The EP-2 bi-polar electrics used by the Milwaukee Road compensated for this problem by using a large number of powered axles.

Modern electric locomotives, like their Diesel-electric counterparts, almost universally use axle-hung traction motors, with one motor for each powered axle. In this arrangement, one side of the motor housing is supported by plain bearings riding on a ground and polished journal that is integral to the axle. The other side of the housing has a tongue-shaped protuberance that engages a matching slot in the truck (bogie) bolster, its purpose being to act as a torque reaction device, as well as a support. Power transfer from motor to axle is effected by spur gearing, in which a pinion on the motor shaft engages a bull gear on the axle. Both gears are enclosed in a liquid-tight housing containing lubricating oil. The type of service in which the locomotive is used dictates the gear ratio employed. Numerically high ratios are commonly found on freight units, whereas numerically low ratios are typical of passenger engines.

Wheel arrangements

The Whyte notation system for classifying steam locomotives is not adequate for describing the varieties of electric locomotive arrangements, though the Pennsylvania Railroad applied classes to its electric locomotives as if they were steam or concatenations of such. For example, the PRR GG1 class indicates that it is arranged like two 4-6-0 class G locomotives that are coupled back-to-back.

In any case, the UIC classification system was typically used for electric locomotives, as it could handle the complex arrangements of powered and unpowered axles, and could distinguish between coupled and uncoupled drive systems.

Electric traction around the world

United States

In the United States it was estimated that it cost as much to electrify a railroad as it cost to build it in the first place. Overhead lines and third rails require greater clearances, and the right-of-way must be better separated to protect the public from electrocution, as well as from trains which approach much more quietly than diesels or steam.

For most large systems the cost of electrifying the whole system is impractical, and generally only some divisions are electrified. In the United States only certain dense urban areas and some mountainous areas were electrified, and the latter have all been discontinued. The junction between electrified and unelectrified territory is the locale of engine changes; for example, Amtrak trains had extended stops in New Haven, Connecticutmarker as diesel and electric locomotives were swapped, a delay which contributed to the electrification of the remaining segment of the Northeast Corridor in 2000.

In North America, the flexibility of diesel locomotives and the relative low cost of their infrastructure has led them to prevail except where legal or other operational constraints dictate the use of electricity. An example of the latter is the use of electric locomotives by AMTRAK and commuter railroads in The Northeast.


NER No.1, Locomotion museum, Shildon

Electrification is widespread in Europe. Due to higher density schedules the operating costs of the locomotives are more dominant with respect to the infrastructure costs than in the US, and electric locomotives have much lower operating costs than diesels. In addition, governments were motivated to electrify their railway networks due to coal shortages during the First and Second World War.

It should also be noted that diesel locomotives have little power compared to electric locomotives, given the same weight and dimensions. For instance, the 2,200 kW of a modern British Rail Class 66 were already met in 1927 by the electric SBB-CFF-FFS Ae 4/7 (2,300 kW), which is even a bit lighter. However, it should be noted that for low speeds tractive effort is more important than power, which is a reason why diesel engines are competitive for slow freight traffic (as it is common in the US), but not for passenger or mixed passenger/freight traffic like on many European railway lines, especially not lines with steep grades like the Gotthardbahn or the Brenner railwaymarker, where heavy freight trains must be run at comparatively high speeds (80 km/h or more).

These factors led to high degrees of electrification in most European countries. In some countries like Switzerland, even electric shunters are common and many private sidings can be served by electric locomotives. During World War 2, when materials to build new electric locomotives were not available, the Swiss Federal Railways installed electric heating elements, fed from the overhead supply, in the boilers of some steam shunters to deal with the shortage of imported coal.

The recent political developments in many European countries to enhance public transit have led to another boost for electric traction. High-speed trains like the TGV, ICE, AVE and Pendolino can only be run economically using electric traction, and the operation of branch lines is usually less in deficit when using electric traction, due to cheaper and faster rolling stock and more passengers due to more frequent service and more comfort. In addition, gaps of unelectrified track are closed to avoid replacing electric locomotives by diesels for these sections. The necessary modernisation and electrification of these lines is possible due to financing of the railroad infrastructure by the state.


Both Victorian Railways and New South Wales Government Railways, which pioneered electric traction in Australia in the early 20th century and continue to operate 1500 V DC Electric Multiple Unit services, have withdrawn their fleets of main line electric locomotives.

In both states, the use of electric locomotives on principal interurban routes proved to be a qualified success. In Victoria, because only one major line (the Gippsland line) had been electrified, the economic advantages of electric traction were not fully realised due to the need to change locomotives for trains that extended beyond the range of the electrified network. VR's entire electric locomotive fleet was withdrawn from service by 1987, and the Gippsland line electrification was dismantled by 2004. Similarly, the new fleet of 86 class locomotives introduced to NSW in 1983 had a relatively short life as the costs of changing locomotives at the extremities of the electrified network, together with the higher charges levied for electricity use, saw diesel-electric locomotives make inroads into the electrified network and the electric locomotive fleet was progressively withdrawn.

Queensland Rail, conversely, implemented electrification relatively recently and utilises the more recent 25 kV AC technology with around 1,000 km of the QR narrow gauge network now electrified. It operates a fleet of electric locomotives to transport coal for export, the most recent of which are those of the 3,000 kW (4,020 HP) 3300/3400 Class. Queensland Rail is currently rebuilding its 3100 and 3200 class locos into the 3700 class, which use AC traction and only need three locos on a coal train rather than five. Queensland Rail is getting thirty 3800 class locos from Siemens in Munich Germany, which will arrive late 2008 to 2009.


In India both AC and DC type of electrified train systems operate today. 1500 V DC based train system is only operating in Mumbai area. It is being converted to 25 kV AC system. Rest of the India where routes are electrified fully operate under 25 kV AC overhead wire.As of 2006, Indian railways haul 80% of freight and 85% of passenger traffic with electric locomotives.


The Trans-Siberian Railway has been partly electrified since 1929 and entirely electric hauled since 2002. The system is 25kV AC 50Hz, and train weights are up to 6000 tonnes.

Battery locomotive

A battery locomotive (or battery-electric locomotive) is a type of electric locomotive powered by on-board batteries; a kind of battery electric vehicle. Such locomotives are used where a conventional diesel or electric locomotive would be unsuitable. An example of use is the hauling of maintenance trains on electrified lines when the electricity supply is turned off, such as by the London Underground battery-electric locomotives.

Another use for battery locomotives is in industrial facilities – as an alternative to the fireless locomotive – where a combustion-powered locomotive (ie steam- or diesel-) could cause a safety issue, due to the risks of fire, explosion or fumes in a confined space.

See also


  1. Renzo Pocaterra, Treni, De Agostini, 2003
  2. B&O Power, Sagle, Lawrence, Alvin Stauffer
  3. Alternating current#Transmission, distribution, and domestic power supply
  4. "New York to Boston, under wire - Amtrak begins all-electric Northeast Corridor service between Boston and Washington, D.C", Railway Age, March 2000, accessed from on 28 Sep. 2006.

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