25 KV AC
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Railway electrification systems using
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 whic ...
(AC) at are used worldwide, especially for high-speed rail. It is usually supplied at the standard
utility frequency The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to t ...
(typically 50 or 60Hz), which simplifies traction substations. The development of 25kV AC electrification is closely connected with that of successfully using utility frequency. This electrification is ideal for railways that cover long distances or carry heavy traffic. After some experimentation before
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
in
Hungary Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Pannonian Basin, Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the ...
and in the
Black Forest The Black Forest (german: Schwarzwald ) is a large forested mountain range in the state of Baden-Württemberg in southwest Germany, bounded by the Rhine Valley to the west and south and close to the borders with France and Switzerland. It is t ...
in
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
, it came into widespread use in the 1950s. One of the reasons why it was not introduced earlier was the lack of suitable small and lightweight control and rectification equipment before the development of solid-state rectifiers and related technology. Another reason was the increased clearance distances required where it ran under bridges and in tunnels, which would have required major
civil engineering Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewa ...
in order to provide the increased clearance to live parts. Railways using older, lower-capacity
direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or eve ...
systems have introduced or are introducing AC instead of DC/ DC for their new high-speed lines.


History

The first successful operational and regular use of a utility frequency system dates back to 1931, tests having run since 1922. It was developed by
Kálmán Kandó Kálmán Kandó de Egerfarmos et Sztregova (''egerfarmosi és sztregovai Kandó Kálmán''; 10 July 1869 – 13 January 1931) was a Hungarian engineer, the inventor of phase converter and a pioneer in the development of AC electric railway tract ...
in Hungary, who used AC at , asynchronous traction, and an adjustable number of (motor) poles. The first electrified line for testing was Budapest–Dunakeszi–Alag. The first fully electrified line was Budapest–Győr–Hegyeshalom (part of the Budapest–Vienna line). Although Kandó's solution showed a way for the future, railway operators outside of Hungary showed a lack of interest in the design. The first railway to use this system was completed in 1936 by the
Deutsche Reichsbahn The ''Deutsche Reichsbahn'', also known as the German National Railway, the German State Railway, German Reich Railway, and the German Imperial Railway, was the German national railway system created after the end of World War I from the regiona ...
who electrified part of the Höllentalbahn between Freiburg and Neustadt installing a 20 kV 50 Hz AC system. This part of Germany was in the French zone of occupation after 1945. As a result of examining the German system in 1951 the SNCF electrified the line between
Aix-les-Bains Aix-les-Bains (, ; frp, Èx-los-Bens; la, Aquae Gratianae), locally simply Aix, is a commune in the southeastern French department of Savoie.
and
La Roche-sur-Foron La Roche-sur-Foron (; Arpitan: ''La Roche'') is a commune in the Haute-Savoie department in the Auvergne-Rhône-Alpes region in Southeastern France. It is located about 23 km (14.2 mi) southeast of Geneva, Switzerland. In 2018, it had a popula ...
in southern France, initially at the same 20kV but converted to 25kV in 1953. The 25kV system was then adopted as standard in France, but since substantial amounts of mileage south of Paris had already been electrified at 1.5kV DC, SNCF also continued some major new DC electrification projects, until dual-voltage locomotives were developed in the 1960s. The main reason why electrification using utility frequency had not been widely adopted before was the lack of reliability of mercury-arc-type rectifiers that could fit on the train. This in turn related to the requirement to use DC series motors, which required the current to be converted from AC to DC and for that a rectifier is needed. Until the early 1950s, mercury-arc rectifiers were difficult to operate even in ideal conditions and were therefore unsuitable for use in railway locomotives. It was possible to use AC motors (and some railways did, with varying success), but they have had less than ideal characteristics for traction purposes. This is because control of speed is difficult without varying the frequency and reliance on voltage to control speed gives a torque at any given speed that is not ideal. This is why DC series motors were the most common choice for traction purposes until the 1990s, as they can be controlled by voltage, and have an almost ideal torque vs speed characteristic. In the 1990s, high-speed trains began to use lighter, lower-maintenance three-phase AC induction motors. The N700 Shinkansen uses a three-level converter to convert single-phase AC to AC (via transformer) to DC (via phase-controlled rectifier with thyristor) to a maximum three-phase AC (via a variable voltage, variable frequency inverter using IGBTs with pulse-width modulation) to run the motors. The system works in reverse for
regenerative braking Regenerative braking is an energy recovery mechanism that slows down a moving vehicle or object by converting its kinetic energy into a form that can be either used immediately or stored until needed. In this mechanism, the electric traction mo ...
. The choice of was related to the efficiency of power transmission as a function of voltage and cost, not based on a neat and tidy ratio of the supply voltage. For a given power level, a higher voltage allows for a lower current and usually better efficiency at the greater cost for high-voltage equipment. It was found that was an optimal point, where a higher voltage would still improve efficiency but not by a significant amount in relation to the higher costs incurred by the need for larger insulators and greater clearance from structures. To avoid
short circuit A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circui ...
s, the high voltage must be protected from moisture. Weather events, such as "
the wrong type of snow "The wrong type of snow" or "the wrong kind of snow" is a phrase coined by the British media in 1991 after severe weather caused disruption to many of British Rail's services. A British Rail press release implied that management and its engine ...
", have caused failures in the past. An example of atmospheric causes occurred in December 2009, when four Eurostar trains broke down inside the Channel Tunnel.


Distribution

Electric power for AC electrification is usually taken directly from the three-phase
transmission system :''See Transmission (mechanics) for a car's transmission system'' In telecommunications, a transmission system is a system that transmits a signal from one place to another. The signal can be an electrical, optical or radio signal. Some transmissi ...
. At the transmission substation, a step-down
transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
is connected across two of the three phases of the high-voltage supply and lowers the voltage to . This is then fed, sometimes several kilometres away, to a railway feeder station located beside the tracks. Since only two phases of the high-voltage supply are used, phase imbalance is corrected by connecting each feeder station to a different combination of phases. To avoid the train pantograph bridging together two feeder stations which may be out-of-phase with each other, neutral sections are provided between sections fed from different feeder stations. SVCs are used for load balancing and voltage control. In some cases dedicated single-phase AC power lines were built to substations with single phase AC transformers. Such lines were built to supply the French
TGV The TGV (french: Train à Grande Vitesse, "high-speed train"; previously french: TurboTrain à Grande Vitesse, label=none) is France's intercity high-speed rail service, operated by SNCF. SNCF worked on a high-speed rail network from 1966 to 19 ...
.


Standardisation

Railway electrification using , AC has become an international standard. There are two main standards that define the voltages of the system: *EN50163:2004+A1:2007 - "Railway applications. Supply voltages of traction systems" *IEC60850 - "Railway Applications. Supply voltages of traction systems" The permissible range of voltages allowed are as stated in the above standards and take into account the number of trains drawing current and their distance from the substation. This system is now part of the European Union's Trans-European railway interoperability standards (1996/48/EC "Interoperability of the Trans-European high-speed rail system" and 2001/16/EC "Interoperability of the Trans-European Conventional rail system").


Variations

Systems based on this standard but with some variations have been used.


25 kV AC at 60 Hz

In countries where is the normal grid power frequency, at is used for the railway electrification. *In
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
on the
Deux-Montagnes line Deux-Montagnes or Two Mountains Line (also designated exo6 and formerly Red Line) was formerly a commuter railway line in Greater Montreal, Quebec, Canada. It was owned by Exo, the organization that operates public transport services across this ...
of the Montreal Metropolitan transportation Agency. *In Japan on the Tokaido, Sanyo and Kyushu
Shinkansen The , colloquially known in English as the bullet train, is a network of high-speed railway lines in Japan. Initially, it was built to connect distant Japanese regions with Tokyo, the capital, to aid economic growth and development. Beyond l ...
lines (using gauge). *In
South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korean Peninsula and sharing a land border with North Korea. Its western border is formed by the Yellow Sea, while its eas ...
on the Korail network. *In
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...
on the
Taiwan High Speed Rail Taiwan High Speed Rail (THSR) is the high-speed railway of Taiwan consisting of one line that runs approximately along the west coast, from the capital Taipei to the southern city of Kaohsiung. With construction and operations managed by a pri ...
line (using gauge) and on
Taiwan Railway Administration Taiwan Railways Administration (TRA) is a railway operator in Taiwan. It is an agency of the Ministry of Transportation and Communications, responsible for managing, maintaining, and running conventional passenger and freight railway services ...
's electrified lines (using gauge). *In the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
on newer electrified portions of the Northeast Corridor (i.e. the New Haven-Boston segment) intercity passenger lines,
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 U.S. state of New Jersey, along with portions of New York State and Pennsylvania. It operates bu ...
commuter lines,
Denver Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the Unit ...
RTD Commuter Rail RTD Bus and Rail (branded as TheRide) is a transit system in the Denver, Colorado, metropolitan area. Operated by the Regional Transportation District (RTD), it currently runs 86 local, 23 regional, 14 limited, and 3 skyRide bus routes plus so ...
and select isolated short lines. In the
San Francisco Bay Area The San Francisco Bay Area, often referred to as simply the Bay Area, is a populous region surrounding the San Francisco, San Pablo, and Suisun Bay estuaries in Northern California. The Bay Area is defined by the Association of Bay Area Go ...
,
Caltrain Caltrain (reporting mark JPBX) is a California commuter rail line serving the San Francisco Peninsula and Santa Clara Valley (Silicon Valley). The southern terminus is in San Jose at Tamien station with weekday rush hour service running as fa ...
is currently undergoing an electrification project, to be completed in the mid-2020s.


20 kV AC at 50 or 60 Hz

In Japan, this is used on existing railway lines in Tohoku Region, Hokuriku Region,
Hokkaido is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The lar ...
and Kyushu, of which Hokuriku and Kyushu are at 60 Hz.


12.5 kV AC at 60 Hz

Some lines in the United States have been electrified at or converted from to . Use of allows direct supply from the 60Hz utility grid yet does not require the larger wire clearance for or require dual-voltage capability for trains also operating on lines. Examples are: * Metro-North Railroad's
New Haven Line The Metro-North Railroad New Haven Line is a commuter rail line running from New Haven, Connecticut to New York City. It joins the Harlem Line at Mount Vernon, New York and continues south to Grand Central Terminal in Manhattan. The New Haven ...
from Pelham, NY to New Haven, CT (Since 1985; previously 11kV 25Hz).


12 kV at 25 Hz

* New Jersey Transit's
North Jersey Coast Line The North Jersey Coast Line is a commuter rail line running from Rahway to Bay Head, New Jersey, traversing through the Jersey Shore region. Operated by New Jersey Transit, the line is electrified as far south as Long Branch. On rail system m ...
from Matawan, NJ to Long Branch, NJ (1988–2002; changed to 25kV 60Hz). *
Amtrak The National Railroad Passenger Corporation, doing business as Amtrak () , is the national passenger railroad company of the United States. It operates inter-city rail service in 46 of the 48 contiguous U.S. States and nine cities in Canada ...
*
SEPTA The Southeastern Pennsylvania Transportation Authority (SEPTA) is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly 4 million people in five c ...
- Both ex- Reading Rail and ex- Pennsylvania Rail sides.


6.25 kV AC

Early 50Hz AC railway electrification in the United Kingdom was planned to use sections at where there was limited clearance under bridges and in tunnels. Rolling stock was dual-voltage with automatic switching between and . The sections were converted to as a result of research work that demonstrated that the distance between live and earthed equipment could be reduced from that originally thought to be necessary. The research was done using a steam engine beneath a bridge at Crewe. A section of overhead line was gradually brought closer to the earthed metalwork of the bridge whilst being subjected to steam from the locomotive's chimney. The distance at which a flashover occurred was measured and this was used as a basis from which new clearances between overhead equipment and structures were derived.


50 kV AC

Occasionally is doubled to to obtain greater power and increase the distance between substations. Such lines are usually isolated from other lines to avoid complications from interrunning. Examples are: *The Sishen–Saldanha iron ore railway (). *The Deseret Power Railway which was an isolated coal railway (). *The now closed
Black Mesa and Lake Powell Railroad The Black Mesa and Lake Powell Railroad was an electrified private railroad operating in Northern Arizona, USA within the Navajo Nation which transported coal from the Peabody Energy Kayenta Mine near Kayenta, Arizona to the Navajo Generating ...
which was also an isolated coal railway (). *The now closed
Tumbler Ridge Tumbler Ridge is a district municipality in the foothills of the B.C. Rockies in northeastern British Columbia, Canada, and a member municipality of the Peace River Regional District. With a population of 2,399 (2021) living in a townsite, the ...
Subdivision of
BC Rail BC Rail is a railway in the Canadian province of British Columbia. Chartered as a private company in 1912 as the Pacific Great Eastern Railway (PGE), it was acquired by the provincial government in 1918. In 1972 it was renamed to the British ...
().


2 × 25 kV autotransformer system

The 2 × 25kV
autotransformer An autotransformer is an electrical transformer with only one winding. The " auto" (Greek for "self") prefix refers to the single coil acting alone, not to any kind of automatic mechanism. In an autotransformer, portions of the same winding act a ...
system is a
split-phase electric power A split-phase or single-phase three-wire system is a type of single-phase electric power distribution. It is the alternating current (AC) equivalent of the original Edison Machine Works three-wire direct-current system. Its primary advantage is t ...
system which supplies 25kV power to the trains, but transmits power at 50kV to reduce energy losses. It should not be confused with the 50kV system. In this system, the current is mainly carried between the overhead line and a feeder transmission line instead of the rail. The overhead line (3) and feeder (5) are on opposite phases so the voltage between them is 50kV, while the voltage between the overhead line (3) and the running rails (4) remains at 25kV. Periodic autotransformers (9) divert the return current from the neutral rail, step it up, and send it along the feeder line. This system is used by
Indian Railways Indian Railways (IR) is a statutory body under the ownership of Ministry of Railways, Government of India that operates India's national railway system. It manages the fourth largest national railway system in the world by size, with a tota ...
,
Russian Railways Russian Railways (russian: link=no, ОАО «Российские железные дороги» (ОАО «РЖД»), OAO Rossiyskie zheleznye dorogi (OAO RZhD)) is a Russian fully state-owned vertically integrated railway company, both manag ...
, Italian High Speed Railways, UK High Speed 1, most of the West Coast Main Line and Crossrail, with some parts of older lines being gradually converted, French lines (LGV lines and some other lines), most Spanish high-speed rail lines,
Amtrak The National Railroad Passenger Corporation, doing business as Amtrak () , is the national passenger railroad company of the United States. It operates inter-city rail service in 46 of the 48 contiguous U.S. States and nine cities in Canada ...
and some of the Finnish and Hungarian lines.


Boosted voltage

For
TGV world speed record The TGV (''Train à Grande Vitesse'', French for "High-Speed Train") holds a series of land speed records for rail vehicles achieved by SNCF, the French national railway, and its industrial partners. The high-speed trials are intended to ex ...
runs in France the voltage was temporarily boosted, to 29.5kV and 31kV at different times.


25 kV on broad gauge lines

* In
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
on the
Roca Line The Roca line is a gauge commuter rail service in the Buenos Aires Province, Argentina, part of General Roca Railway network. The service is currently operated by State-owned company Trenes Argentinos, from the city-centre terminus of Const ...
(using gauge). * In Australia: **
Adelaide Adelaide ( ) is the capital city of South Australia, the state's largest city and the fifth-most populous city in Australia. "Adelaide" may refer to either Greater Adelaide (including the Adelaide Hills) or the Adelaide city centre. The dem ...
: part of the suburban network (). *
Commonwealth of Independent States The Commonwealth of Independent States (CIS) is a regional intergovernmental organization in Eurasia. It was formed following the dissolution of the Soviet Union in 1991. It covers an area of and has an estimated population of 239,796,010. ...
: parts of the network (). *
Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...
: see
rail transport in Finland The Finnish railway network consists of a total track length of of railways built with broad commonly known as Russian gauge track, of which of track is electrified. Passenger trains are operated by the state-owned enterprise VR that runs se ...
(). *
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
: see
rail transport in India Rail transport in India is an important mode of conveyance for people and goods in India. Indian Railways (IR) is the primary operator of rail operations throughout the country. IR is a state-owned organisation of the Ministry of Railways, whi ...
and
Central Organisation for Railway Electrification The Central Organisation for Railway Electrification (CORE) is an organizational unit of Indian Railways responsible for railway electrification of the Indian Railways network. The organisation, founded in 1979, is headquartered in Prayagraj, ...
(). *
Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of ...
: see
list of railway lines in Portugal This is a list of railway lines in Portugal. List Sources * {{Railway lines in Portugal Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the ...
().


25 kV on narrow gauge lines

*In Australia: **
Perth Perth is the capital and largest city of the Australian state of Western Australia. It is the fourth most populous city in Australia and Oceania, with a population of 2.1 million (80% of the state) living in Greater Perth in 2020. Perth i ...
: entire suburban network, see
Transperth Train Operations Transperth Train Operations is a division of the Public Transport Authority of Western Australia. It is responsible for operating Perth’s urban passenger rail system, as part of the Transperth network. Perth's passenger rail network covers ...
(). **
Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , establishe ...
: see
rail electrification in Queensland In the late 1970s and 1980s, a significant rail electrification program was completed in the Australian state of Queensland. The electrified Queensland network is the largest in Australia with over 2,000 kilometres electrified, the next biggest i ...
(). *In
Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...
: see
rail transport in Malaysia Rail transport in Malaysia consists of heavy rail (including commuter rail), light rapid transit (LRT), mass rapid transit (MRT), monorails, airport rail links and a funicular railway line. Heavy rail is mostly used for intercity passenger and ...
(). *In
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
: see
North Island Main Trunk The North Island Main Trunk (NIMT) is the main railway line in the North Island of New Zealand, connecting the capital city Wellington with the country's largest city, Auckland. The line is long, built to the New Zealand rail gauge of and se ...
and Auckland railway electrification (). *In
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
: see
rail transport in South Africa Rail transport in South Africa is an important element of the country's transport infrastructure. All major cities are connected by rail, and South Africa's railway system is the most highly developed in Africa. The South African rail industry is ...
(25 and ). *In
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...
: see
rail transport in Taiwan Rail transport in Taiwan consists of (as of 2015) of railway networks. Though no longer as dominant as it once was, rail transport is an extremely important form of transportation in Taiwan due to high population density, especially along the de ...
(). *In
Tunisia ) , image_map = Tunisia location (orthographic projection).svg , map_caption = Location of Tunisia in northern Africa , image_map2 = , capital = Tunis , largest_city = capital , ...
(): see
rail transport in Tunisia Rail Transport in Tunisia is provided by: * Tunisian Railways (SNCFT) * Société des transports de Tunis, manages commuter trains of the Tunis area including metro light rail and TGM in Tunis * Sahel Metro, company and electric train line So ...
().


Other voltages on 50 Hz electrification

*In
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...
, Mont Blanc Tramway and
Chemin de fer du Montenvers The Montenvers Railway or Chemin de fer du Montenvers is a rack railway line in the Haute-Savoie department of France. The line runs from a connection with the SNCF, in Chamonix, to the ''Hotel de Montenvers'' station, at the Mer de Glace, at ...
: *In
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
, Hambachbahn and Nord-Süd-Bahn:


Multi-system locomotives and trains

Trains that can operate on more than one voltage, say 3kV/25kV, are established technologies. Some locomotives in Europe are capable of using four different voltage standards.


See also

*
15 kV AC railway electrification Railway electrification systems using at are used on transport railways in Germany, Austria, Switzerland, Sweden, and Norway. The high voltage enables high power transmission with the lower frequency reducing the losses of the traction mo ...
*
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 ...
*
Rotary phase converter A rotary phase converter, abbreviated RPC, is an electrical machine that converts power from one polyphase system to another, converting through rotary motion. Typically, single-phase electric power is used to produce three-phase electric power ...


References


Further reading

* Keenor, Garry. Overhead line electrification for railways. * * * * * * * * {{DEFAULTSORT:25 Kv Ac Railway Electrification Electric rail transport