Railway electrification
Railway electrification is the use of electric power for the propulsion of rail transport. Electric railways use either electric locomotives, electric multiple units 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 transformers.
Power is supplied to moving trains with a continuous conductor running along the track that usually takes one of two forms: an overhead line, suspended from poles or towers along the track or from structure or tunnel ceilings and contacted by a pantograph, or a third rail mounted at track level and contacted by a sliding "pickup shoe". 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, 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 diesel locomotives. They have no local emissions, an important advantage in tunnels and urban areas. Some electric traction systems provide regenerative braking that turns the train's kinetic energy 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. Historically, concerns of resource independence have played a role in the decision to electrify railway lines. The landlocked Swiss confederation which almost completely lacks oil or coal deposits but has plentiful hydropower electrified its network in part in reaction to supply issues during both World Wars.
Disadvantages of electric traction include: high capital costs that may be uneconomic on lightly trafficked routes, a relative lack of flexibility, and a vulnerability to power interruptions. Electro-diesel locomotives and electro-diesel multiple units 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. There used to be a historical concern for double-stack rail transport regarding clearances with overhead lines but it is no longer universally true, with both Indian Railways and China Railway regularly operating electric double-stack cargo trains under overhead lines.
Railway electrification has constantly increased in the past decades, and as of 2022, electrified tracks account for nearly one-third of total tracks globally.
History
Railway electrification is the development of powering trains and locomotives using electricity instead of diesel or steam power. The history of railway electrification dates back to the late 19th century when the first electric tramways were introduced in cities like Berlin, London, and New York City.In 1881, the first permanent railway electrification in the world was the Gross-Lichterfelde Tramway in Berlin, Germany. Overhead line electrification was first applied successfully by Frank Sprague in Richmond, Virginia in 1887-1888, and led to the electrification of hundreds of additional street railway systems by the early 1890s. The first electrification of a mainline railway was the Baltimore and Ohio Railroad's Baltimore Belt Line in the United States in 1895–96.
The early electrification of railways used direct current power systems, which were limited in terms of the distance they could transmit power. However, in the early 20th century, alternating current power systems were developed, which allowed for more efficient power transmission over longer distances.
In the 1920s and 1930s, many countries worldwide began to electrify their railways. In Europe, Switzerland, Sweden, France, Germany and Italy were among the early adopters of railway electrification. In the United States, the New York, New Haven and Hartford Railroad was one of the first major railways to be electrified.
Railway electrification continued to expand throughout the 20th century, with technological improvements and the development of high-speed trains and commuters. Today, many countries have extensive electrified railway networks with of standard lines in the world, including China, India, Japan, France, Germany, and the United Kingdom. Electrification is seen as a more sustainable and environmentally friendly alternative to diesel or steam power and is an important part of many countries' transportation infrastructure.
Classification
Electrification systems are classified by three main parameters:- Voltage
- Current
- * Direct current
- * Alternating current
- ** Frequency
- Contact system
- * Overhead lines
- * Third rail
- * Fourth rail
- * Ground-level power supply
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, 750VDC 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 covers both standard voltage and non-standard voltage systems.
The permissible range of voltages allowed for the standardised voltages is as stated in standards BSEN50163 and IEC60850. These take into account the number of trains drawing current and their distance from the substation.
Direct current
Overhead lines
1,500V DC is used in Japan, Indonesia, Hong Kong, Ireland, Australia, France, Singapore, the United States. In Slovakia, there are two narrow-gauge lines in the High Tatras. In the Netherlands it is used on the main system, alongside 25kV on the HSL-Zuid and Betuwelijn, and 3,000V south of Maastricht. In Portugal, it is used in the Cascais Line and in Denmark on the suburban S-train system.In the United Kingdom, 1,500VDC was used in 1954 for the Woodhead trans-Pennine route ; the system used regenerative braking, 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, now converted to 25kVAC. It is now only used for the Tyne and Wear Metro. In India, 1,500V DC was the first electrification system launched in 1925 in Mumbai area. Between 2012 and 2016, the electrification was converted to 25kV 50Hz, which is the countrywide system.
3kV DC is used in Belgium, Italy, Spain, Poland, Slovakia, Slovenia, South Africa, Chile, northern Czechia, the former republics of the Soviet Union, and in the Netherlands on a few kilometres between Maastricht and Belgium. It was formerly used by the Milwaukee Road from Harlowton, Montana, to Seattle, across the Continental Divide and including extensive branch and loop lines in Montana, and by the Delaware, Lackawanna and Western Railroad in the United States, and the Kolkata suburban railway in India, before it was converted to 25kV 50Hz.
DC voltages between 600V and 750V are used by most tramways and trolleybus networks, as well as some metro 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 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, currently electrified at 1.5kV DC, to 9kV DC and found that the conversion would allow to use less bulky overhead wires and lower the losses. The line chosen is one of the lines, totalling 6000km, that are in need of renewal.
In the 1960s the Soviets experimented with boosting the overhead voltage from 3 to 6kV. DC rolling stock was equipped with ignitron-based converters to lower the supply voltage to 3kV. The converters turned out to be unreliable and the experiment was curtailed. In 1970 the Ural Electromechanical Institute of Railway Engineers carried out calculations for railway electrification
at, showing that the equivalent loss levels for a system could be achieved with DC voltage between 11 and 16kV. In the 1980s and 1990s was being tested on the October Railway near Leningrad. The experiments ended in 1995 due to the end of funding.