railway electrification system
   HOME

TheInfoList



(the "Skokie Swift"), shown shortly before the conversion to third rail operation in September 2004. A railway electrification system supplies
electric power Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt The watt (symbol: W) is a unit of Power (physics), power or radiant flux. In the International Sy ...
to
railway Rail transport (also known as train transport) is a means of transferring passengers and goods on wheeled vehicles running on rails, which are located on tracks. In contrast to road transport, where the vehicles run on a prepared flat surf ...

railway
train In rail transport, a train is a series of connected vehicles that run along a railway track and Passenger train, transport people or Rail freight transport, freight. The word ''train'' comes from the Old French , derived from the Latin meaning ...

train
s and
tram Preserved Trams_in_Kraków.html"_;"title="Linke-Hofmann-Busch_tram,_in_Trams_in_Kraków">Kraków,_Poland A_tram_(in_North_America_streetcar_or_trolley)_is_a_railroad_car.html" ;"title="Trams_in_Kraków">Kraków,_Poland.html" ;"title="Tra ...

tram
s without an on-board
prime mover Prime mover in science and engineering is a machine or component that converts energy from an energy source into motive power. Prime mover may refer to: Engineering * Prime mover (engine), a component that transforms the flow or changes in pressu ...
or local fuel supply. Electric railways use either
electric locomotive An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or on-board energy storage such as a battery or a supercapacitor. Electric locomotives with on-board fueled prime movers, such as diesel engin ...

electric locomotive
s (hauling passengers or
freight In economics, the word cargo refers in particular to goods or produce being conveyed—generally for Commerce, commercial gain—by water, air or land. "Freight" is the money paid to carry cargo. ''Cargo'' was originally a shipload. Cargo n ...
in separate cars),
electric multiple unit DART 8500 class commuter EMU at Howth Junction railway station An electric multiple unit or EMU is a multiple-unit train consisting of self-propelled carriages using electricity Electricity is the set of physical phenomena associate ...
s ( passenger cars with their own motors) or both. Electricity is typically generated in large and relatively efficient generating stations, transmitted to the railway network and distributed to the trains. Some electric railways have their own dedicated generating stations and transmission lines, but most purchase power from an electric utility. The railway usually provides its own distribution lines, switches, and
transformer A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple Electrical network, circuits. A varying current in any one coil of the transformer produces a varying magnetic flux ...

transformer
s. Power is supplied to moving trains with a (nearly) continuous
conductor Conductor or conduction may refer to: Music * Conductor (music), a person who leads a musical ensemble like, for example, an orchestra. * Conductor (album), ''Conductor'' (album), an album by indie rock band The Comas * Conduction, a type of ...
running along the track that usually takes one of two forms: an
overhead line An overhead line or overhead wire is used to transmit electrical energy to electric trains, trolleybuses or trams. It is known variously as: * Overhead catenary * Overhead contact system (OCS) * Overhead equipment (OHE) * Overhead line equipmen ...
, suspended from poles or towers along the track or from structure or tunnel ceilings, or a
third rail Shoe of NYC Subway car making contact with third rail. In the foreground is the third rail for the adjacent track. A third rail, also known as a live rail, electric rail or conductor rail, is a method of providing electric power to a railwa ...
mounted at track level and contacted by a sliding "
pickup shoeElectric current collectors are used by trolleybuses, trams, electric locomotives or Electric multiple unit, EMUs to carry electrical power from overhead lines or electrical third rails to the electrical equipment of the vehicles. Those for overhead ...
". Both overhead wire and third-rail systems usually use the running rails as the return conductor, but some systems use a separate fourth rail for this purpose. In comparison to the principal alternative, the
diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of the diesel fuel, fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the dies ...
, electric railways offer substantially better energy efficiency, lower emissions, and lower operating costs. Electric locomotives are also usually quieter, more powerful, and more responsive and reliable than diesels. They have no local emissions, an important advantage in tunnels and urban areas. Some electric traction systems provide
regenerative braking Regenerative braking is an energy recovery mechanism that slows down a moving vehicle or object by converting its kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion (physics), motion. ...

regenerative braking
that turns the train's
kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion (physics), motion. It is defined as the work (physics), work needed to accelerate a body of a given mass from rest to its stated velocity. Having gaine ...
back into electricity and returns it to the supply system to be used by other trains or the general utility grid. While diesel locomotives burn petroleum products, electricity can be generated from diverse sources, including renewable energy.P. M. Kalla-Bishop, ''Future Railways and Guided Transport'', IPC Transport Press Ltd. 1972, pp. 8-33 Historically concerns of resource independence have played a role in the decision to electrify railway lines. The landlocked
Swiss confederation ,german: Schweizer(in),french: Suisse(sse), it, svizzero/svizzera or , rm, Svizzer/Svizra , government_type = Federal semi-direct democracy Semi-direct democracy is a type of democracy that combines the mechanisms of direct democracy Image:La ...

Swiss confederation
which almost completely lacks oil or coal deposits but has plentiful
hydropower Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water to Electricity generation, produce electricity or to power machines. This is achieved by energy transformation, converting the Pote ...
electrified its network in part in reaction to supply issues during both World Wars. Disadvantages of electric traction include: high
capital cost Capital costs are fixed, one-time expenses incurred on the purchase of real property, land, buildings, construction, and equipment used in the production of good (economics and accounting), goods or in the rendering of Service (economics), services. ...
s that may be uneconomic on lightly trafficked routes, a relative lack of flexibility (since electric trains need third rails or overhead wires), and a vulnerability to power interruptions.
Electro-diesel locomotive An electro-diesel locomotive (also referred to as a dual-mode or bi-mode locomotive) is a type of locomotive File:R707-loco-victorian-railways.jpg, upright=1.2, An Victorian Railways R class, R class steam locomotive number R707 as operated b ...
s and
electro-diesel multiple unit An electro-diesel multiple unit (EDMU) or bi-mode multiple unit (BMU) is a form of passenger rail car, with permanently or semi-permanently coupled carriages, that can be powered either by an external electricity supply (like an electric multipl ...
s mitigate these problems somewhat as they are capable of running on diesel power during an outage or on non-electrified routes. Different regions may use different supply voltages and frequencies, complicating through service and requiring greater complexity of locomotive power. The limited clearances available under overhead lines may preclude efficient double-stack container service. However, and
China Railway , former_name = China Railway Corporation (2013–2019) , type = State-owned limited company In a limited company, the liability of members or subscribers of the company A company, abbreviated as co., is a Legal personali ...
operate double-stack cargo trains under overhead wires with electric trains. Railway electrification has constantly increased in the past decades, and as of 2012, electrified tracks account for nearly one-third of total tracks globally.


Classification

Electrification systems are classified by three main parameters: *
Voltage Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is the ...

Voltage
*
Current Currents or The Current may refer to: Science and technology * Current (fluid) A current in a fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. ...
**
Direct current Direct current (DC) is one-directional flow Flow may refer to: Science and technology * Flow (fluid) or fluid dynamics, the motion of a gas or liquid * Flow (geomorphology), a type of mass wasting or slope movement in geomorphology * Flow (mathe ...
(DC) **
Alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in which ...
(AC) ***
Frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency. Frequency is measured in Hertz (unit), hertz ( ...

Frequency
* Contact system **
Overhead line An overhead line or overhead wire is an electrical cable that is used to transmit electrical energy to electric locomotives, trolleybuses or trams. It is known variously as: * Overhead catenary * Overhead contact system (OCS) * Overhead equipment ...
s (catenary) **
Third rail Shoe of NYC Subway car making contact with third rail. In the foreground is the third rail for the adjacent track. A third rail, also known as a live rail, electric rail or conductor rail, is a method of providing electric power to a railwa ...
**
Fourth rail (the "Skokie Swift"), shown shortly before the conversion to third rail operation in September 2004. A railway electrification system supplies electric power to railway trains and trams without an on-board prime mover or local fuel supply. ...
Selection of an electrification system is based on economics of energy supply, maintenance, and capital cost compared to the revenue obtained for freight and passenger traffic. Different systems are used for urban and intercity areas; some
electric locomotive An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or on-board energy storage such as a battery or a supercapacitor. Electric locomotives with on-board fueled prime movers, such as diesel engin ...

electric locomotive
s can switch to different supply
voltage Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is the ...

voltage
s to allow flexibility in operation.


Standardised voltages

Six of the most commonly used voltages have been selected for European and international standardisation. Some of 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. There are many other voltage systems used for railway electrification systems around the world, and the
list of railway electrification systems This is a list of the power supply systems that are, or have been, used for tramway and railway electrification systems. Note that the voltages are nominal and vary depending on load and distance from the substation. Many modern trams and trains u ...
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.


Direct current


Overhead systems

1,500 V DC is used in Japan, Indonesia, Hong Kong (parts), Ireland, Australia (parts), France (also using ), New Zealand (
Wellington Wellington ( mi, Te Whanganui-a-TaraTe Whanganui-a-Tara is the Māori name for Wellington Harbour. The term is also used to refer to the city of Wellington Wellington ( mi, Te Whanganui-a-Tara ) is the capital city of New Zealand. It is ...

Wellington
), Singapore (on the
North East MRT Line The North East line (NEL) is the shortest Mass Rapid Transit line in Singapore Singapore (), officially the Republic of Singapore, is a sovereign state, sovereign island city-state in maritime Southeast Asia. It lies about one degree of l ...
), the United States (
Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive maps of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subd ...

Chicago
area on the
Metra Electric The Metra Electric District is an electrified commuter rail line owned and operated by Metra which connects Millennium Station Millennium Station (formerly Randolph Street Terminal; sometimes called Randolph Street station or Randolph/South Wat ...
district and the
South Shore Line The South Shore Line is an electrically powered interurban commuter rail line operated by the Northern Indiana Commuter Transportation District (NICTD) between Millennium Station in downtown Chicago and the South Bend International Airport i ...
interurban The Interurban (or radial railway in Europe and Canada) is a type of electric railway, with streetcar-like electric self-propelled rail cars which run within and between cities or towns. They were very prevalent in North America between 1900 an ...

interurban
line and Link light rail in
Seattle Seattle ( ) is a port, seaport city on the West Coast of the United States. It is the county seat, seat of King County, Washington, King County, Washington (state), Washington. With a 2020 population of 737,015, it is the largest city in bot ...

Seattle
, Washington). In Slovakia, there are two narrow-gauge lines in the High Tatras (one a cog railway). In the Netherlands it is used on the main system, alongside 25 kV on the
HSL-Zuid The HSL-Zuid ( nl, Hogesnelheidslijn Zuid, en, High-speed Line South), is a 125 kilometre-long (78 miles) Dutch high-speed railway line running between the Amsterdam metropolitan area and the Belgium–Netherlands border, Belgian border, w ...
and Betuwelijn, and 3000 V south of
Maastricht Maastricht ( , , ; Limburgish language, Limburgish : ; french: Maestricht ; es, Mastrique ) is a city and a Municipalities of the Netherlands, municipality in the southeastern Netherlands. It is the capital city, capital and largest city of t ...

Maastricht
. In Portugal, it is used in the
Cascais Line The Cascais Line ( pt, Linha de Cascais) is a Portuguese Portuguese may refer to: * anything of, from, or related to the country and ...
and in Denmark on the suburban
S-train File:Berlin SBahn HackescherMarkt east.jpg, 206px, Part of Berlin Stadtbahn. The tracks on the right belong to the S-train system and the trains stop at the Berlin Hackescher Markt station, Hackescher Markt station, while the other two tracks a ...
system (1650 V DC). In the United Kingdom, 1,500 V DC was used in 1954 for the Woodhead trans-Pennine route (now closed); the system used
regenerative braking Regenerative braking is an energy recovery mechanism that slows down a moving vehicle or object by converting its kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion (physics), motion. ...
, 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 East London is a popularly and informally defined part of London, capital of the United Kingdom. By most definitions, it is east of the ancient City of London and north of the River Thames. It broadly comprises the London boroughs of London Bo ...
and
Manchester Manchester () is the most-populous city and metropolitan borough in North West England North West England is one of nine official regions of England and consists of the counties of Cheshire, Cumbria Cumbria ( ) is a ceremonial cou ...

Manchester
, now converted to 25 kV AC. It is now only used for the
Tyne and Wear Metro The Tyne and Wear Metro is an overground and underground light rail rapid transit system serving the metropolitan boroughs of Newcastle upon Tyne, Metropolitan Borough of Gateshead, Gateshead, North Tyneside, South Tyneside and the City of Sunder ...
. In India, 1,500 V DC was the first electrification system launched in 1925 in Mumbai area. Between 2012 and 2016, the electrification was converted to 25 kV 50 Hz, which is the countrywide system. 3 kV DC is used in Belgium, Italy, Spain, Poland, Slovakia, Slovenia, South Africa, Chile, the northern portion of the Czech Republic, the former republics of the
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a Federalism, federal socialist state in Northern Eurasia that existed from 1922 to 1991. Nominally a Political union, union of multiple national Republics of t ...
, and in the Netherlands on a few kilometers between Maastricht and Belgium. It was formerly used by the
Milwaukee Road The Chicago, Milwaukee, St. Paul and Pacific Railroad (CMStP&P), often referred to as the "Milwaukee Road" , was a Class I railroad that operated in the Midwestern United States, Midwest and Pacific Northwest, Northwest of the United States fro ...
from
Harlowton, Montana Harlowton is a city in and the county seat of Wheatland County, Montana, Wheatland County, Montana, United States. The population was 997 at the 2010 United States Census, 2010 census. The city was once the eastern terminus of electric operations ...
, to Seattle, across the Continental Divide and including extensive branch and loop lines in Montana, and by the
Delaware, Lackawanna and Western Railroad The Delaware, Lackawanna & Western Railroad (also known as the DL&W or Lackawanna Railroad) was a U.S. Class 1 railroad that connected Buffalo, New York Buffalo is the List of cities in New York (state), second-largest city in the United State ...
(now
New Jersey Transit New Jersey Transit Corporation, branded as NJ Transit, and often shortened to NJT, is a state-owned public transportation system that serves the US state of New Jersey New Jersey is a U.S. state, state in the Mid-Atlantic States, Mid ...
, converted to 25 kV AC) in the United States, and the
Kolkata suburban railway The Kolkata Suburban Railway is a suburban rail system serving the Kolkata metropolitan area and its surroundings in India India (Hindi: ), officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of count ...

Kolkata suburban railway
(Bardhaman Main Line) in India, before it was converted to 25 kV 50 Hz. DC voltages between 600 V and 800 V are used by most
tram Preserved Trams_in_Kraków.html"_;"title="Linke-Hofmann-Busch_tram,_in_Trams_in_Kraków">Kraków,_Poland A_tram_(in_North_America_streetcar_or_trolley)_is_a_railroad_car.html" ;"title="Trams_in_Kraków">Kraków,_Poland.html" ;"title="Tra ...

tram
ways (streetcars),
trolleybus A trolleybus (also known as trolley bus, trolley coach, trackless trolley, trackless tramin the 1910s and 1920sJoyce, J.; King, J. S.; and Newman, A. G. (1986). ''British Trolleybus Systems'', pp. 9, 12. London: Ian Allan Publishing. .or trolley ...

trolleybus
networks and
underground Underground most commonly refers to: * Subterranea (geography), the regions beneath the surface of the Earth Underground may also refer to: Places Commercial and cultural venues * The Underground (Boston), a music club in the Allston neighborhood ...
(subway) systems as the traction motors accept this voltage without the weight of an on-board transformer.


Medium-voltage DC

Increasing availability of high-voltage semiconductors may allow the use of higher and more efficient DC voltages that heretofore have only been practical with AC. The use of medium-voltage DC electrification (MVDC) would solve some of the issues associated with standard-frequency AC electrification systems, especially possible supply grid load imbalance and the phase separation between the electrified sections powered from different phases, whereas high voltage would make the transmission more efficient. UIC conducted a case study for the conversion of the Bordeaux-Hendaye railway line (France), currently electrified at 1.5 kV DC, to 9 kV DC and found that the conversion would allow to use less bulky overhead wires (saving €20 million per 100 route-km) and lower the losses (saving 2 GWh per year per 100 route-km; equalling about €150,000 p.a.). The line chosen is one of the lines, totalling 6000 km, that are in need of renewal. In the 1960s the Soviets experimented with boosting the overhead voltage from 3 to 6 kV. DC rolling stock was equipped with
ignitron An ignitron is a type of gas-filled tube A gas-filled tube, also commonly known as a discharge tube or formerly as a Plücker tube, is an arrangement of electrodes in a gas within an insulating, temperature-resistant envelope. Gas-filled tub ...

ignitron
-based converters to lower the supply voltage to 3 kV. The converters turned out to be unreliable and the experiment was curtailed. In 1970 experimental works on 12 kV DC system proved a.o. that the equivalent loss levels for a 25 kV AC system could be achieved with DC voltage between 11 and 16 kV. In the 1980s and 1990s experimental 12 kV DC system was being tested on the
October Railway Oktyabrskaya Railway or October Railway (russian: Октябрьская железная дорога) is the subsidiary of RZD, servicing railway lines in the north-west of Russia. It stretches from Moscow's Leningradsky Rail Terminal, Leningrad T ...
near Leningrad (now ). The experiments ended in 1995 due to the end of funding.


Third rail

Most electrification systems use overhead wires, but third rail is an option up to 1,500 V. Third rail systems almost exclusively use DC distribution. The use of AC is usually not feasible due to the dimensions of a third rail being physically very large compared with the
skin depth s use stranded coils to reduce losses due to the skin effect. Skin effect is the tendency of an alternating current, alternating electric current (AC) to become distributed within a conductor such that the current density In electromagnetism ...

skin depth
that AC penetrates to in a steel rail. This effect makes the resistance per unit length unacceptably high compared with the use of DC. Third rail is more compact than overhead wires and can be used in smaller-diameter tunnels, an important factor for subway systems.


Fourth rail

left, A train on Milan Metro's Line 1 showing the fourth-rail contact shoe. The
London Underground The London Underground (also known simply as the Underground, or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...

London Underground
in England is one of the few networks that uses a four-rail system. The additional rail carries the electrical return that, on third rail and overhead networks, is provided by the running rails. On the London Underground, a top-contact third rail is beside the track, energized at DC, and a top-contact fourth rail is located centrally between the running rails at DC, which combine to provide a traction voltage of DC. The same system was used for
Milan Milan (, , Milanese: ; it, Milano ) is a city in northern Italy, capital of Lombardy, and the List of cities in Italy, second-most populous city proper in Italy after Rome. The city proper has a population of about 1.4 million, while its ...

Milan
's earliest underground line,
Milan Metro The Milan Metro ( it, Metropolitana di Milano) is the rapid transit Rapid transit or mass rapid transit (MRT), also known as heavy rail, metro, subway, tube, U-Bahn, metropolitana or underground, is a type of high-capacity public transport ...
's line 1, whose more recent lines use an overhead catenary or a third rail. The key advantage of the four-rail system is that neither running rail carries any current. 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. Power-only rails can be mounted on strongly insulating ceramic chairs to minimise current leak, but this is not possible for running rails which have to be seated on stronger metal chairs to carry the weight of trains. However, elastomeric rubber pads placed between the rails and chairs can now solve part of the problem by insulating the running rails from the current return should there be a leakage through the running rails.


Rubber-tyred systems

of an
MP 05 The MP 05 (French : Métro sur Pneu d'appel d'offres de 2005)''Rubber-tyred metro ordered in 2005'' is a rubber-tyred metro, rubber-tyred electric multiple unit with driverless operation ordered by the Régie Autonome des Transports Parisiens, RATP ...
, showing the
flange A flange is a protruded ridge, lip or rim, either external or internal, that serves to increase strength Physical strength *Physical strength, as in people or animals *Hysterical strength, extreme strength occurring when people are in life- ...

flange
d steel wheel inside the
rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, ...

rubber
- one, as well as the vertical
contact shoe Electric current collectors are used by trolleybuses, trams, electric locomotives or Electric multiple unit, EMUs to carry electrical power from overhead lines or electrical third rails to the electrical equipment of the vehicles. Those for overhead ...
on top of the left, Bogie">Image:Bogie-metro-Meteor-p1010692.jpg, left, Bogie from an MP 89 Paris Métro vehicle. The lateral
contact shoe Electric current collectors are used by trolleybuses, trams, electric locomotives or Electric multiple unit, EMUs to carry electrical power from overhead lines or electrical third rails to the electrical equipment of the vehicles. Those for overhead ...
is located between the rubber tyres A few lines of the Paris Métro in France operate on a four-rail power system. The trains rubber-tyred metro, move on rubber tyres which roll on a pair of narrow roll ways made of steel and, in some places, of concrete. Since the tyres do not conduct the return current, the two guide bars provided outside the running 'roll ways' become, in a sense, a third and fourth rail which each provide 750 Volt, V Direct current, DC, so at least electrically it is a four-rail system. Each wheelset (rail transport), wheel set of a powered bogie carries one traction motor. A side sliding (side running)
contact shoe Electric current collectors are used by trolleybuses, trams, electric locomotives or Electric multiple unit, EMUs to carry electrical power from overhead lines or electrical third rails to the electrical equipment of the vehicles. Those for overhead ...
picks up the current from the vertical face of each guide bar. The return of each traction motor, as well as each Railroad car, wagon, is effected by one contact shoe each that slide on top of each one of the Rail profile, running rails. This and all other rubber-tyred metros that have a Track (rail transport), track between the roll ways operate in the same manner.


Alternating current

Railways and electrical utilities use AC for the same reason: to use
transformer A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple Electrical network, circuits. A varying current in any one coil of the transformer produces a varying magnetic flux ...

transformer
s, which require AC, to produce higher voltages. The higher the voltage, the lower the current for the same power, which reduces line loss, thus allowing higher power to be delivered. Because alternating current is used with high voltages, this method of electrification is only used on
overhead line An overhead line or overhead wire is used to transmit electrical energy to electric trains, trolleybuses or trams. It is known variously as: * Overhead catenary * Overhead contact system (OCS) * Overhead equipment (OHE) * Overhead line equipmen ...
s, never on third rails. Inside the locomotive, a transformer steps the voltage down for use by the traction motors and auxiliary loads. An early advantage of AC is that the power-wasting resistors used in DC locomotives for speed control were not needed in an AC locomotive: multiple taps on the
transformer A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple Electrical network, circuits. A varying current in any one coil of the transformer produces a varying magnetic flux ...

transformer
can supply a range of voltages. Separate low-voltage transformer windings supply lighting and the motors driving auxiliary machinery. More recently, the development of very high power semiconductors has caused the classic DC motor to be largely replaced with the three-phase induction motor fed by a variable frequency drive, a special inverter that varies both frequency and voltage to control motor speed. These drives can run equally well on DC or AC of any frequency, and many modern electric locomotives are designed to handle different supply voltages and frequencies to simplify cross-border operation.


Low-frequency alternating current

Five European countries, Germany, Austria, Switzerland, Norway and Sweden, have standardized on 15 kV  Hz (the 50 Hz mains frequency divided by three) single-phase AC. On 16 October 1995, Germany, Austria and Switzerland changed from  Hz to 16.7 Hz which is no longer exactly one-third of the grid frequency. This solved overheating problems with the rotary converters used to generate some of this power from the grid supply. Railroad electrification in the United States, In the US, the Electrification of the New York, New Haven, and Hartford Railroad, New York, New Haven, and Hartford Railroad, the Pennsylvania Railroad#Electrification, Pennsylvania Railroad and the Reading Company#Philadelphia and Reading Railway: 1896–1923, Philadelphia and Reading Railway adopted 11 kV 25 Hz single-phase AC. Parts of the original electrified network still operate at 25 Hz, with voltage boosted to 12 kV, while others were converted to 12.5 or 25 kV 60 Hz. In the UK, the London, Brighton and South Coast Railway pioneered overhead electrification of its suburban lines in London, London Bridge station, London Bridge to London Victoria station, Victoria being opened to traffic on 1 December 1909. Victoria to Crystal Palace railway station, Crystal Palace via Balham and West Norwood opened in May 1911. Peckham Rye railway station, Peckham Rye to West Norwood railway station, West Norwood opened in June 1912. Further extensions were not made owing to the First World War. Two lines opened in 1925 under the Southern Railway (Great Britain), Southern Railway serving Coulsdon North railway station, Coulsdon North and Sutton railway station (London), Sutton railway station.History of Southern Electrification
Part 1

Part 2
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-powered electric service ran in September 1929.


Standard frequency alternating current

25 kV AC is used at 60 Hz on some US lines, in western Japan, South Korea and Taiwan; and at 50 Hz in a number of European countries, India, eastern Japan, countries that used to be part of the Soviet Union, on high-speed lines in much of Western Europe (incl. countries that still run conventional railways under DC but not in countries using 16.7 Hz, see above). On "French system" HSLs, the overhead line and a "sleeper" feeder line each carry 25 kV in relation to the rails, but in opposite phase so they are at 50 kV from each other; autotransformers equalize the tension at regular intervals.


Comparisons


AC versus DC for mainlines

The majority of modern electrification systems take AC energy from a power grid that is delivered to a locomotive, and within the locomotive, Transformer, transformed and Rectifier, rectified to a lower DC voltage in preparation for use by traction motors. These motors may either be DC motors which directly use the DC or they may be 3-phase AC motors which require further conversion of the DC to variable frequency 3-phase AC (using power electronics). Thus both systems are faced with the same task: converting and transporting high-voltage AC from the power grid to low-voltage DC in the locomotive. The difference between AC and DC electrification systems lies in where the AC is converted to DC: at the substation or on the train. Energy efficiency and infrastructure costs determine which of these is used on a network, although this is often fixed due to pre-existing electrification systems. Both the transmission and conversion of electric energy involve losses: ohmic losses in wires and power electronics, magnetic field losses in transformers and smoothing reactors (inductors). Power conversion for a DC system takes place mainly in a railway substation where large, heavy, and more efficient hardware can be used as compared to an AC system where conversion takes place aboard the locomotive where space is limited and losses are significantly higher. However, the higher voltages used in many AC electrification systems reduce transmission losses over longer distances, allowing for fewer substations or more powerful locomotives to be used. Also, the energy used to blow air to cool transformers, power electronics (including rectifiers), and other conversion hardware must be accounted for. Standard AC electrification systems use much higher voltages than standard DC systems. One of the advantages of raising the voltage is that, to transmit certain level of power, lower current is necessary (). Lowering the current reduces the ohmic losses and allows for less bulky, lighter overhead line equipment and more spacing between traction substations, while maintaining power capacity of the system. On the other hand, the higher voltage requires larger isolation gaps, requiring some elements of infrastructure to be larger. The standard-frequency AC system may introduce imbalance to the supply grid, requiring careful planning and design (as at each substation power is drawn from two out of three phases). The low-frequency AC system may be powered by Traction power network, separate generation and distribution network or a network of converter substations, adding the expense, also low-frequency transformers, used both at the substations and on the rolling stock, are particularly bulky and heavy. The DC system, apart from being limited as to the maximum power that can be transmitted, also can be responsible for electrochemical corrosion due to stray DC currents.


Electric versus diesel


Energy efficiency

Electric trains need not carry the weight of prime mover (locomotive), prime movers, transmission and fuel. This is partly offset by the weight of electrical equipment. Regenerative braking returns power to the electrification system so that it may be used elsewhere, by other trains on the same system or returned to the general power grid. This is especially useful in mountainous areas where heavily loaded trains must descend long grades. Central station electricity can often be generated with higher efficiency than a mobile engine/generator. While the efficiency of power plant generation and diesel locomotive generation are roughly the same in the nominal regime, diesel motors decrease in efficiency in non-nominal regimes at low power while if an electric power plant needs to generate less power it will shut down its least efficient generators, thereby increasing efficiency. The electric train can save energy (as compared to diesel) by
regenerative braking Regenerative braking is an energy recovery mechanism that slows down a moving vehicle or object by converting its kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion (physics), motion. ...
and by not needing to consume energy by idling as diesel locomotives do when stopped or coasting. However, electric rolling stock may run cooling blowers when stopped or coasting, thus consuming energy. Large fossil fuel power stations operate at high efficiency, and can be used for district heating or to produce district cooling, leading to a higher total efficiency.


Power output

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') but, at higher speeds, this proves costly and impractical. Therefore, almost all high speed trains are electric. The high power of electric locomotives also 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 train weights are to be increased on a system. On the other hand, electrification may not be suitable for lines with low frequency of traffic, because lower running cost of trains may be outweighed by the high cost of the electrification infrastructure. Therefore, most long-distance lines in developing or sparsely populated countries are not electrified due to relatively low frequency of trains.


Network effect

Network effects are a large factor with electrification. When converting lines to electric, the connections with other lines must be considered. Some electrifications have subsequently 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 electro-diesel locomotive, dual mode engines must be used. This is mostly an issue for long-distance trips, but many lines come to be dominated by through traffic from long-haul freight trains (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. A problem specifically related to electrified lines are gaps in the electrification. Electric vehicles, especially locomotives, lose power when traversing gaps in the supply, such as phase change gaps in overhead systems, and gaps over points in third rail systems. These become a nuisance, if the locomotive stops with its collector on a dead gap, in which case there is no power to restart. Power gaps can be overcome by on-board batteries or motor-flywheel-generator systems. In 2014, progress is being made in the use of large capacitors to power electric vehicles between stations, and so avoid the need for overhead wires between those stations.


Maintenance costs

Maintenance costs of the lines may be increased by electrification, but many systems claim lower costs due to reduced wear-and-tear on the track from lighter rolling stock. There are some additional maintenance costs associated with the electrical equipment around the track, such as power sub-stations and the catenary wire itself, but, if there is sufficient traffic, the reduced track and especially the lower engine maintenance and running costs exceed the costs of this maintenance significantly.


Sparks effect

Newly electrified lines often show a "sparks effect", whereby electrification in passenger rail systems leads to significant jumps in patronage / revenue. The reasons may include electric trains being seen as more modern and attractive to ride, faster and smoother service, and the fact that electrification often goes hand in hand with a general infrastructure and rolling stock overhaul / replacement, which leads to better service quality (in a way that theoretically could also be achieved by doing similar upgrades yet without electrification). Whatever the causes of the sparks effect, it is well established for numerous routes that have electrified over decades.


Double-stack rail transport

Due to the Loading gauge, height restriction imposed by the overhead wires, double-stacked container trains have been traditionally difficult and rare to operate under electrified lines. However, this limitation is being overcome by railways in India, China and Africa by laying new tracks with increased catenary height. Such installations are in the Western Dedicated Freight Corridor in India where the wire height is at 7.45 metres to accommodate double-stack container trains without the need of Class U special wagon, well-wagons.


Advantages

* No exposure to passengers to exhaust from the locomotive * Lower cost of building, running and maintaining locomotives and multiple units * Higher power-to-weight ratio (no onboard fuel tanks), resulting in ** Fewer locomotives ** Faster acceleration ** Higher practical limit of power ** Higher limit of speed * Less noise pollution (quieter operation) * Faster acceleration clears lines more quickly to run more trains on the track in urban rail uses * Reduced power loss at higher altitudes (for ''power loss'' see Diesel engine) * Independence of running costs from fluctuating fuel prices * Service to underground stations where diesel trains cannot operate for safety reasons * Reduced environmental pollution, especially in highly populated urban areas, even if electricity is produced by fossil fuels * Easily accommodates kinetic energy brake reclaim using supercapacitors * More comfortable ride on multiple units as trains have no underfloor diesel engines * Somewhat higher energy efficiency in part due to
regenerative braking Regenerative braking is an energy recovery mechanism that slows down a moving vehicle or object by converting its kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion (physics), motion. ...
and less power lost when "idling" * More flexible primary energy source: can use coal, nuclear or renewable energy (hydro, solar, wind) as the primary energy source instead of diesel oil * If the entire network is electrified, diesel infrastructure such as fueling stations, maintenance yards and indeed the diesel locomotive fleet can be retired or put to other uses - this is often the business case in favor of electrifying the last few lines in a network where otherwise costs would be too high. Having only one type of motive power also allows greater fleet homogeneity which can also reduce costs.


Disadvantages

* 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 Structure gauge, obstructions have to be altered for Engineering tolerance#Clearance (civil engineering, clearance. Another aspect that can raise the cost of electrification are the alterations or upgrades to railway signalling needed for new traffic characteristics, and to protect signalling circuitry and track circuits from interference by traction current. Electrification may require line closures while the new equipment is being installed. * Appearance: the overhead line structures and cabling can have a significant landscape impact compared with a non-electrified or third rail electrified line that has only occasional signalling equipment above ground level. * Fragility and vulnerability: overhead electrification systems can suffer severe disruption due to minor mechanical faults or the effects of high winds causing the Pantograph (transport), pantograph of a moving train to become entangled with the Overhead line#Overhead catenary, catenary, ripping the wires from their supports. The damage is often not limited to the supply to one track, but extends to those for adjacent tracks as well, causing the entire route to be blocked for a considerable time. Third-rail systems can suffer disruption in cold weather due to ice forming on the conductor rail. * Theft: the high scrap value of copper and the unguarded, remote installations make overhead cables an attractive target for scrap metal thieves. Attempts at theft of live 25 kV cables may end in the thief's death from electrocution. In the UK, cable theft is claimed to be one of the biggest sources of delay and disruption to train services – though this normally relates to signalling cable, which is equally problematic for diesel lines. * Incompatibility: Diesel trains can run on any track without electricity or with any kind of electricity (
third rail Shoe of NYC Subway car making contact with third rail. In the foreground is the third rail for the adjacent track. A third rail, also known as a live rail, electric rail or conductor rail, is a method of providing electric power to a railwa ...
or
overhead line An overhead line or overhead wire is used to transmit electrical energy to electric trains, trolleybuses or trams. It is known variously as: * Overhead catenary * Overhead contact system (OCS) * Overhead equipment (OHE) * Overhead line equipmen ...
, DC or AC, and at any voltage or frequency). Not so electric trains, which can never run on non-electrified lines, and which even on electrified lines can run only on the single, or the few, electrical system(s) for which they are equipped. Even on fully electrified networks, it is usually a good idea to keep a few diesel locomotives for maintenance and repair trains, for instance to repair broken or stolen overhead lines, or to lay new tracks. However, due to ventilation issues, diesel trains may have to be banned from certain tunnels and underground train stations mitigating the advantage of diesel trains somewhat. * Birds may perch on parts with different charges, and animals may also touch the electrification system. Dead animals attract foxes or other predators, bringing risk of collision with trains. * In most of the world's railway networks, the height clearance of overhead electrical lines is not sufficient for a double-stack container car or other unusually tall loads. It is extremely costly to upgrade electrified lines to the correct clearances () to take double-stacked container trains.


World electrification

As of 2012, electrified tracks account for nearly one third of total tracks globally. As of 2018, there were of railways electrified at 25 kV, either 50 or 60 Hz; electrified at 3 kV DC; electrified at 15 kV 16.7 or  Hz and electrified at 1.5 kV DC. The Swiss rail network is the largest fully electrified network in the world and one of only two to achieve this, the other being Armenia. India and China have the largest electrified railway length with just over 70% of the network. A number of countries have zero electrification length. Several countries have announced plans to electrify all or most of their railway network such as and Israel Railways.


See also

* Battery electric multiple unit * Battery locomotive * Conduit current collection * Current collector * Dual electrification * Electromote * Ground-level power supply * Electric locomotive#History, History of the electric locomotive * Electrification of the New York, New Haven, and Hartford Railroad#Initial Electrification Experiments, Initial Electrification Experiments NY NH HR * List of railway electrification systems * List of tram systems by gauge and electrification * Multi-system (rail) * Overhead line#Overhead conductor rails, Overhead conductor rails * Railroad electrification in the United States * Stud contact system * Traction current pylon * Traction powerstation * Traction substation


References


Sources


English

* * Gomez-Exposito A., Mauricio J.M., Maza-Ortega J.M. "VSC-based MVDC Railway Electrification System" IEEE transactions on power delivery, v.29, no.1, Feb.2014 pp. 422–431. (suggests 24 kV DC)
(Jane's) Urban Transit Systems
* * *


Russian

* Винокуров В.А., Попов Д.А. "Электрические машины железно-дорожного транспорта" (Electrical machinery of railroad transportation), Москва, Транспорт, 1986. , 520 pp. * Дмитриев, В.А., "Народнохозяйственная эффективность электрификации железных дорог и применения тепловозной тяги" (National economic effectiveness of railway electrification and application of diesel traction), Москва, Транспорт 1976. * Дробинский В.А., Егунов П.М. "Как устроен и работает тепловоз" (How the diesel locomotive works) 3rd ed. Moscow, Транспорт, 1980. * Иванова В.Н. (ed.) "Конструкция и динамика тепловозов" (Construction and dynamics of the diesel locomotive). Москва, Транспорт, 1968 (textbook). * Калинин, В.К. "Электровозы и электропоезда" (Electric locomotives and electric train sets) Москва, Транспорт, 1991 * Мирошниченко, Р.И., "Режимы работы электрифицированных участков" (Regimes of operation of electrified sections [of railways]), Москва, Транспорт, 1982. * Перцовский, Л. М.; "Энергетическая эффективность электрической тяги" (Energy efficiency of electric traction), Железнодорожный транспорт (magazine), #12, 1974 p. 39+ * Плакс, А.В. & Пупынин, В. Н., "Электрические железные дороги" (Electric Railways), Москва "Транспорт" 1993. * Сидоров Н.И., Сидорожа Н.Н. "Как устроен и работает электровоз" (How the electric locomotive works) Москва, Транспорт, 1988 (5th ed.) - 233 pp, . 1980 (4th ed.). * Хомич А.З. Тупицын О.И., Симсон А.Э. "Экономия топлива и теплотехническая модернизация тепловозов" (Fuel economy and the thermodynamic modernization of diesel locomotives) - Москва: Транспорт, 1975 - 264 pp.


External links


Railway Technical Web Page

Electrified railways
{{DEFAULTSORT:Railway electrification system Electric rail transport, *