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A traction substation, traction current converter plant, rectifier station or traction power substation (TPSS) is an electrical substation that converts electric power from the form provided by the electrical power industry for public utility service to an appropriate voltage, current type and frequency to supply railways, trams (streetcars) or trolleybuses with traction current.
These systems can be used to convert three-phase 50 Hz or 60 Hz alternating current (AC) for the supply of AC railway electrification systems at a lower frequency and single phase, as used by many older systems, or to rectify AC into direct current (DC) for those systems (primarily public transit systems) using DC for traction power. The three-phase voltage from the local utility is stepped down and rectified in the traction substations to provide the required DC voltage.
Originally, the conversion equipment usually consisted of one or more motor-generator sets containing three-phase synchronous AC motors and single-phase AC generators, mechanically coupled to a common shaft. Rotary converters were also used, especially where the desired output was DC current from an AC source.
In the 1920s, DC was derived using electronic valves (mercury arc rectifiers). In modern systems, high-voltage DC (HVDC) "back-to-back" stations are used instead of mechanical equipment to convert between different frequencies and phases of AC power and solid-state thyristor rectifier systems are used for conversion from AC power to DC traction power.
Traction current converter plants are either decentralized (where one plant directly supplies the overhead lines or third rail of the traction system, with no feed into a traction current distribution network) or centralized (for the supply of the traction power network, usually in addition to the direct supply of the overhead lines or third rail).
Central traction current converter plants are generally found in Germany (primarily in the cities of Neckarwestheim, Ulm, Nuremberg), Austria and Switzerland, while decentralized traction current converter plants are generally found in Norway, Sweden and the German states of Mecklenburg-Vorpommern and Brandenburg as well as parts of Great Britain. A List of railway electrification systems provides further detail.
An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature. Occasionally, a linear alternator or a rotating armature with a stationary magnetic field is used. In principle, any AC electrical generator can be called an alternator, but usually the term refers to small rotating machines driven by automotive and other internal combustion engines.
A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the opposite of rectifiers which were originally large electromechanical devices converting AC to DC.
The utility frequency, (power) line frequency or mains frequency is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to the end-user. In large parts of the world this is 50 Hz, although in the Americas and parts of Asia it is typically 60 Hz. Current usage by country or region is given in the list of mains electricity by country.
A railway electrification system supplies electric power to railway trains and trams without an on-board prime mover or local fuel supply. 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.
A motor–generator is a device for converting electrical power to another form. Motor–generator sets are used to convert frequency, voltage, or phase of power. They may also be used to isolate electrical loads from the electrical power supply line. Large motor–generators were widely used to convert industrial amounts of power while smaller motor–generators were used to convert battery power to higher DC voltages.
A rotary converter is a type of electrical machine which acts as a mechanical rectifier, inverter or frequency converter.
An HVDC converter station is a specialised type of substation which forms the terminal equipment for a high-voltage direct current (HVDC) transmission line. It converts direct current to alternating current or the reverse. In addition to the converter, the station usually contains:
A traction network or traction power network is an electricity grid for the supply of electrified rail networks. The installation of a separate traction network generally is done only if the railway in question uses alternating current (AC) with a frequency lower than that of the national grid, such as in Germany, Austria and Switzerland.
Railway electrification systems using alternating current (AC) at 25 kilovolts (kV) are used worldwide, especially for high-speed rail.
Railway electrification systems using alternating current (AC) at 15 kilovolts (kV) and 16.7 hertz (Hz) 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 motors that were available at the beginning of the 20th century. Railway electrification in late 20th century tends to use 25 kV, 50 Hz AC systems which has become the preferred standard for new railway electrifications but extensions of the existing 15 kV networks are not completely unlikely. In particular, the Gotthard Base Tunnel still uses 15 kV, 16.7 Hz electrification.
A frequency changer or frequency converter is an electronic or electromechanical device that converts alternating current (AC) of one frequency to alternating current of another frequency. The device may also change the voltage, but if it does, that is incidental to its principal purpose, since voltage conversion of alternating current is much easier to achieve than frequency conversion.
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 locally to run three-phase loads in premises where only single-phase is available.
A phase converter is a device that converts electric power provided as single phase to multiple phase or vice versa. The majority of phase converters are used to produce three-phase electric power from a single-phase source, thus allowing the operation of three-phase equipment at a site that only has single-phase electrical service. Phase converters are used where three-phase service is not available from the utility, or is too costly to install due to a remote location. A utility will generally charge a higher fee for a three-phase service because of the extra equipment, including transformers, metering, and distribution wire.
Amtrak's 25 Hz traction power system is a traction power grid operated by Amtrak along the southern portion of its Northeast Corridor (NEC): the 226.6 route miles (362 km) between Washington, D.C. and New York City and the 104 route miles (167 km) between Philadelphia and Harrisburg, Pennsylvania. The Pennsylvania Railroad constructed it between 1915 and 1938. Amtrak inherited the system from Penn Central, the successor to the Pennsylvania Railroad, in 1976, along with the Northeast Corridor. This is the reason for using 25 Hz, as opposed to 60 Hz, which is the standard for power transmission in North America. In addition to serving the NEC, the system provides power to NJ Transit Rail Operations (NJT), the Southeastern Pennsylvania Transportation Authority (SEPTA) and the Maryland Area Regional Commuter Train (MARC). Only about half of the system's electrical capacity is used by Amtrak. The remainder is sold to the commuter railroads who operate their trains along the corridor.
A rotary converter plant is a facility at which rotary converters convert one form of electricity to another form of electricity. The installed combinations of motors and generators at a plant determine the possible type(s) of conversion. Such facilities also allow the setting of voltages and frequencies, if appropriate equipment is installed. Rotary converter plants were commonplace in railway electrification before the invention of mercury arc rectifiers in the 1920s.
The New York, New Haven and Hartford Railroad pioneered electrification of main line railroads using high-voltage, alternating current, single-phase overhead catenary. It electrified its mainline between Stamford, Connecticut, and Woodlawn, New York, in 1907, and extended the electrification to New Haven, Connecticut, in 1914. While single-phase AC railroad electrification has become commonplace, the New Haven's system was unprecedented at the time of construction. The significance of this electrification was recognized in 1982 by its designation as a National Historic Engineering Landmark by the American Society of Mechanical Engineers (ASME).
The Norwegian railway network consists of 2,552 kilometers (1,586 mi) of electrified railway lines, constituting 62% of the Norwegian National Rail Administration's 4,114 kilometers (2,556 mi) of line. In 2008, electric traction accounted for 90% of the passenger kilometers, 93% of the tonne kilometers and 74% of the energy consumption of all trains running in Norway, with the rest being accounted for by diesel traction.
The Seebach-Wettingen railway electrification trial (1905-1909) was an important milestone in the development of electric railways. Maschinenfabrik Oerlikon (MFO) demonstrated the suitability of single-phase alternating current at high voltage for long-distance railway operation with the Seebach-Wettingen single-phase alternating current test facility. For this purpose, MFO electrified the 19.45-kilometre-long Swiss Federal Railways (SBB) route from Seebach to Wettingen at its own expense with single-phase alternating current at 15,000 volts.