Railway electrification system - AbsoluteAstronomy.com

A railway electrification system supplies electrical energy

Electric potential energy

Electric potential energy, or electrostatic potential energy, is a potential energy that results from conservative Coulomb forces and is associated with the configuration of a particular set of point charges within a defined system...

to railway locomotives

Electric locomotive

An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or an on-board energy storage device...

and multiple units

Electric multiple unit

An electric multiple unit or EMU is a multiple unit train consisting of self-propelled carriages, using electricity as the motive power. An EMU requires no separate locomotive, as electric traction motors are incorporated within one or a number of the carriages...

as well as tram

Tram

A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...

s so that they can operate without having an on-board prime mover

Prime mover (locomotive)

In engineering, a prime mover is an engine that converts fuel to useful work. In locomotives, the prime mover is thus the source of power for its propulsion. The term is generally used when discussing any locomotive powered by an internal combustion engine...

. There are several different electrification systems in use throughout the world. Railway electrification has many advantages but requires significant capital expenditure for installation.

Characteristics of electric traction

The main advantage of electric traction is a higher power-to-weight ratio

Power-to-weight ratio

Power-to-weight ratio is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power sources...

than traction systems such as diesel

Diesel engine

A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

or steam

Steam

Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...

that generate power on board, but which must carry their own fuel supply. Electricity enables faster acceleration

Acceleration

In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

and higher tractive effort on steep gradients. On locomotives equipped with regenerative brake

Regenerative brake

A regenerative brake is an energy recovery mechanism which slows a vehicle or object down by converting its kinetic energy into another form, which can be either used immediately or stored until needed...

s, descending gradients require very little use of air brakes as the locomotive's traction motors become generators sending current back into the supply system to be used by other vehicles, and/or on-board resistors, which convert the excess energy to heat.

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 less carbon emissions than diesel trains, especially in countries where electricity comes primarily from non-fossil sources.

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, so unless multi-system

Multi-system (rail)

A Multi-system locomotive is one that is able to operate using more than one railway electrification system, such as the British Rail Class 92 which can operate from both 750 V DC third rail and 25 kV, 50 Hz AC from overhead lines.As well as multi-system electric...

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. 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.

Classification

Electrification systems are classified by three main parameters:

Voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
Current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
- Direct current
  Direct current
  Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
  
  (DC)
- Alternating current
  Alternating current
  In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
  
  (AC)
  - Frequency
    Frequency
    Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

Contact System
- third rail
  Third rail
  A third rail is a method of providing electric power to a railway train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway track. It is used typically in a mass transit or rapid transit system, which has alignments in its own corridors, fully or almost...
- overhead line
  Overhead lines
  Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point...
  
  (catenary)

Standardised voltages

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, 750 V DC may be used with either third rail or overhead lines (the latter normally by trams).

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.

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.

Electrification system	Lowest non-permanent voltage	Lowest permanent voltage	Nominal voltage	Highest permanent voltage	Highest non-permanent voltage
600 V DC Direct current Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...	400 V	400 V	600 V	720 V	800 V
750 V DC	500 V	500 V	750 V	900 V	1 kV
1,500 V DC	1,000 V	1,000 V	1,500 V	1,800 V	1,950 V
3 kV DC	2 kV	2 kV	3 kV	3 kV	3 kV
15 kV AC, 16.7 Hz	11 kV	12 kV	15 kV	17.25 kV	18 kV
25 kV AC, 50 Hz	17.5 kV	19 kV	25 kV	27.5 kV	29 kV

Direct current

Early electric systems used low-voltage DC

Direct current

Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

. Electric motor

Electric motor

An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

s were fed directly from the traction supply and were controlled using a combination of resistor

Resistor

A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...

s and relay

Relay

A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...

s that connected the motors in parallel

Series and parallel circuits

Components of an electrical circuit or electronic circuit can be connected in many different ways. The two simplest of these are called series and parallel and occur very frequently. Components connected in series are connected along a single path, so the same current flows through all of the...

or series

Series and parallel circuits

.

The most common DC voltages are 600 V and 750 V for tram

Tram

s and metro

Rapid transit

A rapid transit, underground, subway, elevated railway, metro or metropolitan railway system is an electric passenger railway in an urban area with a high capacity and frequency, and grade separation from other traffic. Rapid transit systems are typically located either in underground tunnels or on...

s and 1,500 V, 650/750 V third rail for the former Southern Region

Southern Region of British Railways

The Southern Region was a region of British Railways from 1948. The region ceased to be an operating unit in its own right in the 1980s and was wound up at the end of 1992. The region covered south London, southern England and the south coast, including the busy commuter belt areas of Kent, Sussex...

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. Suburban trains (S-Bahn)

S-Bahn

S-Bahn refers to an often combined city center and suburban railway system metro in Austria, Germany, Switzerland and Denmark...

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. 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 fourth (centre) rail connected to the running rails in inter-running areas.

During the mid-20th century, rotary converter

Rotary converter

A rotary converter is a type of electrical machine which acts as a mechanical rectifier or inverter. It was used to convert AC to DC or DC to AC power before the advent of chemical or solid state power rectification...

s or mercury arc rectifiers

Mercury arc valve

A mercury-arc valve is a type of electrical rectifier used for converting high-voltage or high-current alternating current into direct current . Rectifiers of this type were used to provide power for industrial motors, electric railways, streetcars, and electric locomotives, as well as for...

were used to convert utility (mains) AC power to the required DC voltage at feeder stations. Today, this is usually done by semiconductor

Semiconductor

A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

rectifier

Rectifier

A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...

s after stepping down the voltage from the utility supply.

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

Copper loss

Copper loss is the term often given to heat produced by electrical currents in the conductors of transformer windings, or other electrical devices. Copper losses are an undesirable transfer of energy, as are core losses, which result from induced currents in adjacent components...

. In the United Kingdom, the maximum current that can be drawn by a train is 6,800 A at 750 V . The feeder stations require constant monitoring. 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 (15.5 mi).

If auxiliary machinery, such as fans

Fan (implement)

A hand-held fan is an implement used to induce an airflow for the purpose of cooling or refreshing oneself. Any broad, flat surface waved back-and-forth will create a small airflow and therefore can be considered a rudimentary fan...

and compressors

Gas compressor

A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...

, 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. 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). Now solid-state converters (SIVs) and fluorescent lights can be used.

Overhead systems

1,500 V DC is used in the Netherlands, Japan, Hong Kong (parts), Ireland

Republic of Ireland

Ireland , described as the Republic of Ireland , is a sovereign state in Europe occupying approximately five-sixths of the island of the same name. Its capital is Dublin. Ireland, which had a population of 4.58 million in 2011, is a constitutional republic governed as a parliamentary democracy,...

, Australia (parts), India (around the Mumbai

Mumbai

Mumbai , formerly known as Bombay in English, is the capital of the Indian state of Maharashtra. It is the most populous city in India, and the fourth most populous city in the world, with a total metropolitan area population of approximately 20.5 million...

area alone, to be converted to 25 kV AC like the rest of the country), France, New Zealand (Wellington

Wellington

Wellington is the capital city and third most populous urban area of New Zealand, although it is likely to have surpassed Christchurch due to the exodus following the Canterbury Earthquake. It is at the southwestern tip of the North Island, between Cook Strait and the Rimutaka Range...

) and the United States (Chicago area on the Metra Electric

Metra Electric Line

The Metra Electric District is an electrified commuter rail line owned and operated by Metra which connects Millennium Station in downtown Chicago, with the city's southern suburbs...

district and the South Shore Line

South Shore Line (NICTD)

The South Shore Line is an electrically powered interurban commuter rail line operated by the Northern Indiana Commuter Transportation District between Millennium Station in downtown Chicago and the South Bend Regional Airport in South Bend, Indiana...

interurban

Interurban

An interurban, also called a radial railway in parts of Canada, is a type of electric passenger railroad; in short a hybrid between tram and train. Interurbans enjoyed widespread popularity in the first three decades of the twentieth century in North America. Until the early 1920s, most roads were...

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

S-Train

The S-train network is a combined urban rapid transit and suburban rail network of Metropolitan Copenhagen, Denmark. It connects the city center with the inner suburbs of Copenhagen, and has close to half of the stations within the urban city. The first line was opened in 1934...

system.

In the United Kingdom, 1,500 V DC was used in 1954 for the Woodhead

Manchester-Sheffield-Wath electric railway

The Manchester-Sheffield-Wath electric railway was an early electrification scheme on British railways. The route featured long ascents on both sides of the Pennines with the long Woodhead Tunnel at its central summit close to the Woodhead pass...

trans-Pennine route (now closed); the system used regenerative braking

Regenerative brake

, allowing for transfer of energy between climbing and descending trains on the steep approaches to the tunnel. The system was also used for suburban electrification in East London and Manchester

Manchester

Manchester is a city and metropolitan borough in Greater Manchester, England. According to the Office for National Statistics, the 2010 mid-year population estimate for Manchester was 498,800. Manchester lies within one of the UK's largest metropolitan areas, the metropolitan county of Greater...

, now converted to 25 kV AC.

3 kV DC is used in Belgium, Italy, Spain, Poland, the northern Czech Republic, Slovakia

Slovakia

The Slovak Republic is a landlocked state in Central Europe. It has a population of over five million and an area of about . Slovakia is bordered by the Czech Republic and Austria to the west, Poland to the north, Ukraine to the east and Hungary to the south...

, Slovenia

Slovenia

Slovenia , officially the Republic of Slovenia , is a country in Central and Southeastern Europe touching the Alps and bordering the Mediterranean. Slovenia borders Italy to the west, Croatia to the south and east, Hungary to the northeast, and Austria to the north, and also has a small portion of...

, western Croatia

Croatia

Croatia , officially the Republic of Croatia , is a unitary democratic parliamentary republic in Europe at the crossroads of the Mitteleuropa, the Balkans, and the Mediterranean. Its capital and largest city is Zagreb. The country is divided into 20 counties and the city of Zagreb. Croatia covers ...

, South Africa and former Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

countries (also using 25 kV 50 Hz AC). It was formerly used by the Milwaukee Road

Chicago, Milwaukee, St. Paul and Pacific Railroad

The Milwaukee Road, officially the Chicago, Milwaukee, St. Paul and Pacific Railroad , was a Class I railroad that operated in the Midwest and Northwest of the United States from 1847 until its merger into the Soo Line Railroad on January 1, 1986. The company went through several official names...

's extensive electrification across the Continental Divide and by the Delaware, Lackawanna & Western Railroad

Delaware, Lackawanna and Western Railroad

The Delaware, Lackawanna and Western Railroad Company was a railroad connecting Pennsylvania's Lackawanna Valley, rich in anthracite coal, to Hoboken, New Jersey, , Buffalo and Oswego, New York...

(now New Jersey Transit

New Jersey Transit

The New Jersey Transit Corporation is a statewide public transportation system serving the United States state of New Jersey, and New York, Orange, and Rockland counties in New York State...

, converted to 25 kV AC) in the United States, and the Kolkata suburban railway

Kolkata Suburban Railway

The Kolkata Suburban Railway is the rail system for the suburbs surrounding the city of Kolkata . Railways such as this are important and heavily-used infrastructure in India....

(Bardhaman Main Line) in India, before it was converted to 25 kV 50 Hz AC.

600 V DC is used by Milan

Milan

Milan is the second-largest city in Italy and the capital city of the region of Lombardy and of the province of Milan. The city proper has a population of about 1.3 million, while its urban area, roughly coinciding with its administrative province and the bordering Province of Monza and Brianza ,...

's network of tramways and trolleybuses.

Third rail

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. 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. 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.

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. 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 (160.9 km/h) because above that speed reliable contact between the shoe and the rail cannot be maintained.

Some street tram

Tram

s (streetcars) used conduit third-rail current collection. The third rail was below street level. The tram picked up the current through a plough

Conduit current collection

Conduit current collection is a system of electric current collection used by electric trams, where the power supply is carried in a channel under the roadway, rather than located overhead.-Description:...

(U.S. "plow") accessed through a narrow slot in the road. 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. 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

Kingsway tramway subway

The Kingsway Tramway Subway is a cut-and-cover Grade II Listed tunnel in central London, built by the London County Council, the only one of its kind in Britain...

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, where the abandoned tracks have not been paved over. The slot can easily be confused with the similar looking slot for cable trams/cars (in some cases, the conduit slot was originally a cable slot). The disadvantage of conduit collection included much higher initial installation costs, 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 wire 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 overhead wire. In New York City for the same reasons of cost and operating efficiency outside of Manhattan overhead wire was used. A new approach to avoiding overhead wires is taken by the "second generation" tram/streetcar system in Bordeaux, France (entry into service of the first line in December 2003; original system discontinued in 1958) with its APS

Ground-level power supply

Ground-level power supply, also known as surface current collection and Alimentation par Sol is a modern method of third-rail electrical pick-up for street trams. It was invented for the Bordeaux tramway, which was constructed from 2000 and opened in 2003. Until 2011, this is the only place it is...

(alimentation par sol — ground current feed). This involves a third rail which is 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". 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. This system has also been adopted in some sections of the new tram systems in Reims

Reims

Reims , a city in the Champagne-Ardenne region of France, lies east-northeast of Paris. Founded by the Gauls, it became a major city during the period of the Roman Empire....

, France (opened 2011) and Angers

Angers

Angers is the main city in the Maine-et-Loire department in western France about south-west of Paris. Angers is located in the French region known by its pre-revolutionary, provincial name, Anjou, and its inhabitants are called Angevins....

, France (also opened 2011). Proposals are in place for a number of other new services including Dubai

Dubai

Dubai is a city and emirate in the United Arab Emirates . The emirate is located south of the Persian Gulf on the Arabian Peninsula and has the largest population with the second-largest land territory by area of all the emirates, after Abu Dhabi...

, UAE; Barcelona

Barcelona

Barcelona is the second largest city in Spain after Madrid, and the capital of Catalonia, with a population of 1,621,537 within its administrative limits on a land area of...

, Spain; Florence

Florence

Florence is the capital city of the Italian region of Tuscany and of the province of Florence. It is the most populous city in Tuscany, with approximately 370,000 inhabitants, expanding to over 1.5 million in the metropolitan area....

, Italy; Marseille

Marseille

Marseille , known in antiquity as Massalia , is the second largest city in France, after Paris, with a population of 852,395 within its administrative limits on a land area of . The urban area of Marseille extends beyond the city limits with a population of over 1,420,000 on an area of...

, France; Gold Coast

Gold Coast, Queensland

Gold Coast is a coastal city of Australia located in South East Queensland, 94km south of the state capital Brisbane. With a population approximately 540,000 in 2010, it is the second most populous city in the state, the sixth most populous city in the country, and also the most populous...

, Australia; Washington, D.C.

Washington, D.C.

Washington, D.C., formally the District of Columbia and commonly referred to as Washington, "the District", or simply D.C., is the capital of the United States. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....

, U.S.A.; Brasília

Brasília

Brasília is the capital city of Brazil. The name is commonly spelled Brasilia in English. The city and its District are located in the Central-West region of the country, along a plateau known as Planalto Central. It has a population of about 2,557,000 as of the 2008 IBGE estimate, making it the...

, Brazil and Tours

Tours

Tours is a city in central France, the capital of the Indre-et-Loire department.It is located on the lower reaches of the river Loire, between Orléans and the Atlantic coast. Touraine, the region around Tours, is known for its wines, the alleged perfection of its local spoken French, and for the...

, France. At least initially there were teething troubles in terms of maintaining current feed, 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.

Fourth rail

The London Underground

London Underground

The London Underground is a rapid transit system serving a large part of Greater London and some parts of Buckinghamshire, Hertfordshire and Essex in England...

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. 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. The same system was used for Milan

Milan

's earliest underground line, Milan Metro's

Milan Transportation System

The Milan transportation system is the transport network of Milan, Italy. Milan has an extensive internal transport network and is also an important transportation node in Italy, being one of the country's biggest hub for air, rail and road networks....

line 1, whose more recent lines use an overhead catenary.

This scheme was introduced because of the problems of return currents, intended to be carried by the earthed (grounded) running rail, flowing through the iron tunnel linings instead. This can cause electrolytic damage and even arcing if the tunnel segments are not electrically bonded together. 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 not constructed to carry currents and had no adequate electrical bonding between pipe segments. 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.

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.

On tracks that London Underground share with National Rail

National Rail

National Rail is a title used by the Association of Train Operating Companies as a generic term to define the passenger rail services operated in Great Britain...

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. Underground trains pass from one section to the other at speed; lineside electrical connections and resistances separate the two types of supply.

Fourth-rail trains occasionally operate on the National third-rail system. To do so, the centre-rail shoes are bonded to the wheels. This bonding must be removed before operating again on fourth-rail tracks.

A system proposed (but not used) by the South Eastern and Chatham Railway

South Eastern and Chatham Railway

The South Eastern and Chatham Railway Companies Joint Management Committee , known by its shorter name of the South Eastern and Chatham Railway was a working union of two neighbouring rival railways, the South Eastern Railway and London, Chatham and Dover Railway , that operated services between...

around 1920 was 1,500 V DC four rail. Technical details are scarce but it is likely that it would have been a mid-earth system with one conductor rail at +750 V and the other at −750 V. This would have facilitated conversion to 750 V DC three-rail at a later date.

A few lines of the Paris Métro

Paris Métro

The Paris Métro or Métropolitain is the rapid transit metro system in Paris, France. It has become a symbol of the city, noted for its density within the city limits and its uniform architecture influenced by Art Nouveau. The network's sixteen lines are mostly underground and run to 214 km ...

in France operate on a four-rail power scheme because they run on natural rubber tyres

Tire

A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...

which run on a pair of narrow roadways made of steel and, in some places, concrete. Since the tyres do not conduct the return current, the two guide rails provided outside of the running 'roadways' double up as conductor rails, so at least electrically it fits as a four-rail scheme. One of the guide rails is bonded to the return conventional running rails situated inside the roadway so a single polarity supply is actually required. 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. The loop was originally provided to save the original steam locomotives having to 'run around' the rest of the train saving much time. Today, the driver doesn't have to change ends at termini provided with such a loop, but the time saving is not so significant as it takes almost as long to drive round the loop as it does to change ends. Many of the original loops have been lost as lines were extended.

Alternating current

These are overhead electrification systems

Overhead lines

Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point...

. Alternating current can be transformed

Transformer

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

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 railways.

Low-frequency alternating current

Common DC commutating

Commutator (electric)

A commutator is a rotary electrical switch in certain types of electric motors or electrical generators that periodically reverses the current direction between the rotor and the external circuit. In a motor, it applies power to the best location on the rotor, and in a generator, picks off power...

electric motors can also be fed with AC (universal motor), because reversing the current in both stator

Stator

The stator is the stationary part of a rotor system, found in an electric generator, electric motor and biological rotors.Depending on the configuration of a spinning electromotive device the stator may act as the field magnet, interacting with the armature to create motion, or it may act as the...

and rotor

Rotor (electric)

The rotor is the non-stationary part of a rotary electric motor, electric generator or alternator, which rotates because the wires and magnetic field of the motor are arranged so that a torque is developed about the rotor's axis. In some designs, the rotor can act to serve as the motor's armature,...

does not change the direction of torque

Torque

Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

. However, the inductance

Inductance

In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...

of the windings made early designs of large motors impractical at standard AC distribution frequencies. In addition, AC induces eddy current

Eddy current

Eddy currents are electric currents induced in conductors when a conductor is exposed to a changing magnetic field; due to relative motion of the field source and conductor or due to variations of the field with time. This can cause a circulating flow of electrons, or current, within the body of...

s, particularly in non-laminated field pole pieces, that cause overheating and loss of efficiency. In the previous century, five European countries, including Germany, Austria, Switzerland, Norway and Sweden, standardized on 15 kV 16⅔ Hz (one-third of the normal mains frequency) single-phase AC in an attempt to alleviate such problems. On 16 October 1995, Germany, Austria and Switzerland changed the designation from 16⅔ Hz to a nominal 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) is used at 11 kV between Washington, D.C.

Washington, D.C.

and New York City and between Harrisburg, Pennsylvania

Harrisburg, Pennsylvania

Harrisburg is the capital of Pennsylvania. As of the 2010 census, the city had a population of 49,528, making it the ninth largest city in Pennsylvania...

and Philadelphia. A 12.5 kV 25 Hz section between New York City and New Haven, Connecticut

New Haven, Connecticut

New Haven is the second-largest city in Connecticut and the sixth-largest in New England. According to the 2010 Census, New Haven's population increased by 5.0% between 2000 and 2010, a rate higher than that of the State of Connecticut, and higher than that of the state's five largest cities, and...

was converted to 60 Hz in the last third of the 20th century.

In the UK, the London, Brighton and South Coast Railway

London, Brighton and South Coast Railway

The London, Brighton and South Coast Railway was a railway company in the United Kingdom from 1846 to 1922. Its territory formed a rough triangle, with London at its apex, practically the whole coastline of Sussex as its base, and a large part of Surrey...

pioneered overhead electrification of its suburban lines in London, London Bridge

London Bridge station

London Bridge railway station is a central London railway terminus and London Underground complex in the London Borough of Southwark, occupying a large area on two levels immediately south-east of London Bridge and 1.6 miles east of Charing Cross. It is one of the oldest railway stations in the...

to Victoria being opened to traffic on 1 December 1909. Victoria to Crystal Palace

Crystal Palace railway station

Crystal Palace railway station is in the London Borough of Bromley in south London. It is located in the Anerley area between the town centres of Crystal Palace and Penge...

via Balham and West Norwood opened in May 1911. Peckham Rye

Peckham Rye railway station

Peckham Rye railway station is a station on Rye Lane in the centre of the shopping district of Peckham in South London. It opened on 1 December 1865 for LC&DR trains and on 13 August 1886 for LB&SCR trains...

to West Norwood

West Norwood railway station

West Norwood railway station is in the London Borough of Lambeth in West Norwood, south London. The station, and all trains serving it, is operated by Southern, and it is in Travelcard Zone 3. Services from Platform 1 go to London Victoria and London Bridge via Tulse Hill...

opened in June 1912. Further extensions were not made owing to the First World War. Two lines opened in 1925 under the Southern Railway

Southern Railway (Great Britain)

The Southern Railway was a British railway company established in the 1923 Grouping. It linked London with the Channel ports, South West England, South coast resorts and Kent...

serving Coulsdon North

Coulsdon North railway station

Coulsdon North is a closed railway station on the Brighton Main Line.- Opening :The station was opened as "Stoats Nest and Cane Hill" on 5 November 1899 by the London, Brighton and South Coast Railway . It took its name partly from the nearby Cane Hill asylum and partly from the nearby Stoats Nest...

and Sutton 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.

In such a system, the traction motors can be fed through a transformer

Transformer

with multiple taps. Changing the taps allows the motor voltage to be changed without requiring power-wasting resistor

Resistor

s. Auxiliary machinery is driven by small commutating motors powered from a separate low-voltage winding of the main transformer.

The use of low frequency requires that electricity be converted

Phase converter

A phase converter is a device that converts electric power provided as single phase to multiple phase or vice-versa. The majority of phase converters are used to produce three phase electric power from a single-phase source, thus allowing the operation of three-phase equipment at a site that only...

from utility power by motor-generator

Motor-generator

A motor-generator is a device for converting electrical power to another form. Motor-generator sets are used to convert frequency, voltage, or phase of power. They may also be used to isolate electrical loads from the electrical power supply line...

s or static inverter

Static inverter plant

A static inverter station, also known as an HVDC Converter Station, is the terminal equipment for a high-voltage direct-current transmission line, in which direct current is converted to three-phase alternating current, and, usually, the reverse...

s at the feeding substations, or generated at altogether separate traction powerstation

Traction powerstation

A traction power station is a power station that produces only traction current, that is, electric current used for railways, trams, trolleybuses or other conveyances. Pure traction power stations are rare and there are many more power stations that generate current for other purposes, such as...

s.

Since 1979, the three-phase induction motor

Induction motor

An induction or asynchronous motor is a type of AC motor where power is supplied to the rotor by means of electromagnetic induction. These motors are widely used in industrial drives, particularly polyphase induction motors, because they are robust and have no brushes...

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.

Polyphase alternating current systems

Three-phase AC railway electrification was used in Italy, Switzerland and the United States in the early twentieth century. Italy was the major user, for lines in the mountainous regions of northern Italy from 1901 until 1976. The first lines were the Burgdorf-Thun line in Switzerland (1899), and the lines of the Ferrovia Alta Valtellina from Colico

Colico

Colico is a comune in the province of Lecco, Lombardy, Italy. It is situated near the tip of the northern arm of Lake Como, where the river Adda enters the lake...

to Chiavenna and Tirano

Tirano

Tirano is a town in Valtellina, located in the province of Sondrio, Northern Italy. It has about 9,044 inhabitants and is adjacent to the Switzerland-Italy boundary. The river Adda flows through the town....

in Italy, which were electrified in 1901 and 1902. Other lines where the three-phase system were used were the Simplon Tunnel

Simplon Tunnel

The Simplon Tunnel is an Alpine railway tunnel that connects the Swiss town of Brig with Domodossola in Italy, though its relatively straight trajectory does not run under Simplon Pass itself. It actually consists of two single-track tunnels built nearly 20 years apart...

in Switzerland from 1906 to 1930, and the Cascade Tunnel

Cascade Tunnel

The Cascade Tunnel refers to two tunnels at Stevens Pass through the Cascade Mountains, approximately to the east of Everett, Washington. The first Cascade Tunnel was a 2.63-mile long single track railroad, built by the Great Northern Railway in 1900 to avoid problems caused by heavy winter...

of the Great Northern Railway in the United States from 1909 to 1939.

The early sysems used a low frequency (16⅔ Hz), and a relatively low voltage (3,000 or 3,600 volts) compared with later AC systems. The system provides regenerative braking with the power fed back to the system, so is particularly suitable for mountain railways (provided another locomotive on the line can use the power). The system has the disadvantage of requiring two (or three) separate overhead conductors plus return through the rails for the three phases. Locomotives operate at one, two or four constant speeds.

The system is still used on four mountain railways, using 725 to 3000 V at 50 or 60 Hz: the (Corcovado Rack Railway

Corcovado Rack Railway

The Corcovado Train is a mountain railway in Rio de Janeiro in Brazil, from Cosme Velho to the summit of the Corcovado Mountain at an altitude of . The summit is known for its statue of Christ the Redeemer and its views over the city and beaches of Rio....

in Rio de Janeiro, Brazil

Rio de Janeiro

Rio de Janeiro , commonly referred to simply as Rio, is the capital city of the State of Rio de Janeiro, the second largest city of Brazil, and the third largest metropolitan area and agglomeration in South America, boasting approximately 6.3 million people within the city proper, making it the 6th...

, Jungfraubahn

Jungfraubahn

The Jungfraubahn is an gauge rack railway electrified at 3-phase 1,125 volts 50 Hertz, which runs 9 kilometres from Kleine Scheidegg to the highest railway station in Europe at Jungfraujoch...

and Gornergratbahn

Gornergratbahn

The Gornergratbahn is a nine-kilometre metre-gauge mountain rack railway, with Abt rack system. It leads from Zermatt, Switzerland , up to the Gornergrat...

in Switzerland and the Petit train de la Rhune

Petit train de la Rhune

The Petit train de la Rhune is a metre gauge rack railway in France at the western end of the Pyrenees. It links the Col de Saint-Ignace, some to the east of Saint-Jean-de-Luz, to the summit of the La Rhune mountain...

in France).

Standard frequency alternating current

Only in the 1950s after development in France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

(20 kV then 25 kV) and former Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

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.

The first attempts to use standard-frequency single-phase AC were made in Hungary

Hungary

Hungary , officially the Republic of Hungary , is a landlocked country in Central Europe. It is situated in the Carpathian Basin and is bordered by Slovakia to the north, Ukraine and Romania to the east, Serbia and Croatia to the south, Slovenia to the southwest and Austria to the west. The...

since 1923, by the Hungarian Kálmán Kandó

Kálmán Kandó

Kálmán Kandó de Egerfarmos et Sztregova was a Hungarian engineer, and a pioneer in the development of electric railway traction.-Education:...

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 V. 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

Budapest

Budapest is the capital of Hungary. As the largest city of Hungary, it is the country's principal political, cultural, commercial, industrial, and transportation centre. In 2011, Budapest had 1,733,685 inhabitants, down from its 1989 peak of 2,113,645 due to suburbanization. The Budapest Commuter...

-Hegyeshalom

Hegyeshalom

Hegyeshalom is a village of approximately 3600 inhabitants in the Győr-Moson-Sopron county of Hungary, on the border with Austria and less than 15 km from the border with Slovakia.- History :...

line (towards Vienna

Vienna

Vienna is the capital and largest city of the Republic of Austria and one of the nine states of Austria. Vienna is Austria's primary city, with a population of about 1.723 million , and is by far the largest city in Austria, as well as its cultural, economic, and political centre...

) regularly used the same system. A few decades after the Second World War, the 16 kV was changed to the Russian and later French 25 kV system.

Today, some locomotive

Locomotive

A locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine, first used in the early 19th...

s in this system use a transformer

Transformer

and rectifier

Rectifier

to provide low-voltage pulsating

Pulse-width modulation

Pulse-width modulation , or pulse-duration modulation , is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches....

direct current to motors. Speed is controlled by switching winding taps on the transformer. More sophisticated locomotives use thyristor

Thyristor

A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased .Some sources define silicon controlled rectifiers and...

or IGBT circuitry to generate chopped or even variable-frequency alternating current

Alternating current

In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

(AC) that is then supplied to the AC induction traction motor

Traction motor

Traction motor refers to an electric motor providing the primary rotational torque of a machine, usually for conversion into linear motion ....

s.

This system is quite economical but it has its drawbacks: the phases of the external power system are loaded unequally and there is significant electromagnetic interference

Electromagnetic interference

Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...

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.

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 isolated. 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. 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

Pantograph (rail)

A pantograph for rail lines is a hinged electric-rod device that collects electric current from overhead lines for electric trains or trams. The pantograph typically connects to a one-wire line, with the track acting as the ground wire...

will smoothly run from one section to the other. 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. 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. 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, 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.

On French high-speed rail

High-speed rail

High-speed rail is a type of passenger rail transport that operates significantly faster than the normal speed of rail traffic. Specific definitions by the European Union include for upgraded track and or faster for new track, whilst in the United States, the U.S...

lines, the UK High Speed 1 Channel Tunnel rail link and in the Channel Tunnel

Channel Tunnel

The Channel Tunnel is a undersea rail tunnel linking Folkestone, Kent in the United Kingdom with Coquelles, Pas-de-Calais near Calais in northern France beneath the English Channel at the Strait of Dover. At its lowest point, it is deep...

, neutral sections are negotiated automatically.

In Japanese Shinkansen

Shinkansen

The , also known as THE BULLET TRAIN, is a network of high-speed railway lines in Japan operated by four Japan Railways Group companies. Starting with the Tōkaidō Shinkansen in 1964, the network has expanded to currently consist of of lines with maximum speeds of , of Mini-shinkansen with a...

lines, there are ground-operated switched sections installed instead of neutral sections. The sections detect trains running within the section and automatically switch the power supply in 0.3 s, which eliminates needs of shutting off powers at any moment.

World electrification

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.

Advantages

Advantages include:

lower running cost of locomotives and multiple unit
Multiple unit
The term multiple unit or MU is used to describe a self-propelled carriages capable of coupling with other units of the same or similar type and still being controlled from one driving cab. The term is commonly used to denote passenger trainsets consisting of more than one carriage...

s
lower maintenance cost of locomotives and multiple unit
Multiple unit
The term multiple unit or MU is used to describe a self-propelled carriages capable of coupling with other units of the same or similar type and still being controlled from one driving cab. The term is commonly used to denote passenger trainsets consisting of more than one carriage...

s
higher power-to-weight ratio, resulting in
- fewer locomotives
- faster acceleration
- higher practical limit of power
- higher limit of speed
less noise pollution (quieter operation)
reduced power loss at higher altitudes (for power loss see Diesel engine
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

)
independent from crude oil fuel
reduced environmental pollution, even if electricity is produced by fossil fuels

Disadvantages

Disadvantages include:

Electrification cost: electrification requires an entire new infrastructure to be built around the existing tracks at a significant cost. Costs are especially high when tunnels, bridges and other obstructions have to be altered for clearance
Structure gauge
The structure gauge, also called the minimum clearance outline, is the minimum height and width of tunnels and bridges as well as the minimum height and width of the doors that allow a rail siding access into a warehouse...

. Another aspect that can raise the cost of electrification are the alterations or upgrades to railway signalling
Railway signalling
Railway signalling is a system used to control railway traffic safely, essentially to prevent trains from colliding. Being guided by fixed rails, trains are uniquely susceptible to collision; furthermore, trains cannot stop quickly, and frequently operate at speeds that do not enable them to stop...

needed for new traffic characteristics.
Electrical grid load: adding a major new consumer of electricity can have adverse effects on the electrical grid and may necessitate an increase in the grid's power output.

Trade-offs

Trade-offs include:

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.

Network effect
Network effect
In economics and business, a network effect is the effect that one user of a good or service has on the value of that product to other people. When network effect is present, the value of a product or service is dependent on the number of others using it.The classic example is the telephone...

s 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. If through traffic is to have any benefit, time consuming engine switches must occur to make such connections or expensive dual mode engines
Electro-diesel locomotive
An Electro-diesel locomotive is powered either from an electricity supply or by using the onboard diesel engine...

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 (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. 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.

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. 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. 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.

Summary

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. 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. For passenger operation it is possible to provide enough power with diesel engines (see e.g. 'ICE TD
ICE TD
The DBAG Class 605 is a high-speed diesel multiple unit train, in service with Deutsche Bahn and DSB, commonly known as the ICE TD.- Development :...

') but, at higher speeds, this proves costly and impractical. Therefore, almost all high speed train
High-speed rail
High-speed rail is a type of passenger rail transport that operates significantly faster than the normal speed of rail traffic. Specific definitions by the European Union include for upgraded track and or faster for new track, whilst in the United States, the U.S...

s are electric.
The high power of electric locomotives gives them the ability to pull freight at higher speed over gradients; 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.

Energy efficiency

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 smaller carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

footprint. Some of the reasons include:

electric trains are generally lighter than self powered versions (e.g. diesel traction);
- they do not have to carry the weight of prime movers
  Prime mover (locomotive)
  In engineering, a prime mover is an engine that converts fuel to useful work. In locomotives, the prime mover is thus the source of power for its propulsion. The term is generally used when discussing any locomotive powered by an internal combustion engine...
  
  , transmission and fuel.
- 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.).

the electricity may be generated from various energy sources which are more efficient than a diesel engine
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

, as well as lessening reliance on petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

products and reducing carbon dioxide emissions, including;
- nuclear power
  Nuclear power
  Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...
  
  ,
- renewable resources (e.g. hydroelectricity
  Hydroelectricity
  Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...
  
  , wind generation, etc.),
- large fossil fuel
  Fossil fuel
  Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...
  
  using power station
  Power station
  A power station is an industrial facility for the generation of electric energy....
  
  s with greater efficiency (although they may still have a relatively large carbon footprint).

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;
  - often implemented in tram
    Tram
    A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...
    
    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,
  - on mountainous lines where trains may be scheduled such that one is ascending whilst another descends;
- in some form of energy storage
  Energy storage
  Energy storage is accomplished by devices or physical media that store some form of energy to perform some useful operation at a later time. A device that stores energy is sometimes called an accumulator....
  
  , such as flywheel energy storage
  Flywheel energy storage
  Flywheel energy storage works by accelerating a rotor to a very high speed and maintaining the energy in the system as rotational energy...
  
  so that it may be used later (e.g. to accelerate a train from a station at which it has recently stopped)
- some systems, such as most systems in the UK, are able to return excess energy to the public network.

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). 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. Rail electrification is often considered an important route towards consumption pattern reform.

External cost

The external cost

Externality

In economics, an externality is a cost or benefit, not transmitted through prices, incurred by a party who did not agree to the action causing the cost or benefit...

of railway is lower than other modes of transport but the electrification brings it down further if it is sustainable

Sustainability

Sustainability is the capacity to endure. For humans, sustainability is the long-term maintenance of well being, which has environmental, economic, and social dimensions, and encompasses the concept of union, an interdependent relationship and mutual responsible position with all living and non...

.

Also, the lower cost of energy from well to wheel

Life cycle assessment

A life-cycle assessment is a technique to assess environmental impacts associated with all the stages of a product's life from-cradle-to-grave A life-cycle assessment (LCA, also known as life-cycle analysis, ecobalance, and cradle-to-grave analysis) is a technique to assess environmental impacts...

and the ability to reduce pollution and greenhouse gas in the atmosphere according to the Kyoto Protocol

Kyoto Protocol

The Kyoto Protocol is a protocol to the United Nations Framework Convention on Climate Change , aimed at fighting global warming...

is an advantage.

Non-contact systems

It is possible to supply power to an electric train by inductive coupling

Inductive coupling

In electrical engineering, two conductors are referred to as mutual-inductively coupled or magnetically coupled when they are configured such that change in current flow through one wire induces a voltage across the ends of the other wire through electromagnetic induction...

. This allows the use of a high-voltage, insulated, conductor rail. Such a system was patented in 1894 by Nikola Tesla, US Patent 514972. It requires the use of high-frequency alternating current. Tesla did not specify a frequency but George Trinkaus suggests that around 1,000 Hz would be likely.

Inductive coupling is widely used in low-power applications, such as re-chargeable electric toothbrush

Electric toothbrush

An electric toothbrush is a toothbrush that uses electric power supplied usually by a battery to move the brush head rapidly, either oscillating side to side, or rotation-oscillation .- History :...

es. The contactless technology for rail vehicles is currently being marketed by Bombardier as PRIMOVE.

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.
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

Gate turn-off thyristor

A gate turn-off thyristor is a special type of thyristor, a high-power semiconductor device. GTOs, as opposed to normal thyristors, are fully controllable switches which can be turned on and off by their third lead, the GATE lead.-Device description:...

) to IGBT (Insulated-gate bipolar transistor) for more powerful locomotives with higher reliability is one of the elements of Technology roadmap

Technology roadmap

A technology roadmap is a plan that matches short-term and long-term goals with specific technology solutions to help meet those goals. It is a plan that applies to a new product or process, or to an emerging technology. Developing a roadmap has three major uses...

(TRM) and the loop to have a mature system as in Maturity road mapping with the Technology transfer

Technology transfer

Technology Transfer, also called Transfer of Technology and Technology Commercialisation, is the process of skill transferring, knowledge, technologies, methods of manufacturing, samples of manufacturing and facilities among governments or universities and other institutions to ensure that...

provision.

External links

Railway Technical Web Page

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Characteristics of electric traction

Classification

Standardised voltages

Direct current

Overhead systems

Third rail

Fourth rail

Alternating current

Low-frequency alternating current

Polyphase alternating current systems

Standard frequency alternating current

World electrification

Advantages

Disadvantages

Trade-offs

Summary

Energy efficiency

External cost

Non-contact systems

Research and development

See also

External links