Applications
Dedicated traction current lines are used when railways are supplied with low-frequency alternating current (AC). The traction current supply line is connected to substations along the line of the railway and is usually run separately from the overhead catenary wire from which the locomotives are fed.
In countries in which the electric trains run with direct current or with single-phase alternating current with the frequency of the general power grid, the required conversion of the current is performed in the substations, so again no traction current lines are required.
Traction current supply lines are not usually laid parallel to the railway line, in order to allow a shorter line length and to avoid unnecessary influences to the electrical system near the railway line; this also is applied to the current supply of some rapid-transit railways operating with alternating current in Germany.
It is also possible to lay out the traction current supply on special cross beams right on the overhead wire pylons above the catenary wire. Because the overhead line pylons have a smaller cross section than traction current supply masts, the cross beams cannot be too wide, so the standard arrangement of four conductor cables in one level cannot be used. In this case, a two-level arrangement is used, or with two electric circuits for double-railed lines the overhead line pylons for both directions are equipped with cross beams for their own traction current system of two conductor cables each.
In densely populated areas, there are pylons which carry circuits for both traction current and for three-phase alternating current for general power. Such lines are found where rights of way are rare. In particular the parallel route of 110 kV and 220 kV three-phase AC is common. The use of 380 kV power lines on the same pylon requires 220 kV insulators for the traction current line, because in case the 380 kV line fails, voltage spikes can occur along the traction current line, which the 110 kV insulators cannot handle.
As a rule, traction current lines use single conductors, however for the supply of railways with high traffic and in particular for the supply of high speed railway lines, two bundle conductors are used.
Characteristics
Traction current lines are used to power the railway systems of countries which use alternating current of a lower frequency than the public supply. This is typically the case in the German-speaking countries of Europe. For example, 16.7 Hz AC is used in Germany, Austria and Switzerland.
A specific example is the Mariazeller narrow gauge railway in Austria, operating with single phase AC with a frequency of 25 Hz, which has its own traction current lines with an operating voltage of 27 kV. These lines are mounted on the pylons of the overhead wire over the lines.
The voltages used for traction current lines are 110 kV in Germany and Austria and 66 kV or 132 kV in Switzerland.
Traction current lines are operated symmetrically against earth. In the case of 110 kV lines, for example, each conductor has a voltage of 55 kV against earth. The grounding is made in larger substations and in power stations for traction current, using transformers for the cancellation of the earth leakage current. As is the case for all symmetrical powerlines there are also at traction power lines twisting points. A traction powerline for one circuit has usually two conductors. Since most traction current lines possess two electric circuits, four conductors are on the pylons as a rule (in contrast with three-phase alternating current lines, whose number of conductors are an integral multiple of three).
Routing of traction current lines
Traction current lines are not usually laid parallel to the railway line, so as to minimise the line length and to avoid unnecessary influences of electrical system near the railway line. However, there are cases where this practice is not followed (for example, the current supply of some rapid-transit railways operating with alternating current in Germany). In this case, the traction current line is laid on special cross beams of the overhead wire pylons above the overhead line. Because overhead line pylons possess a smaller cross section than traction current masts, these cross beams have to be quite narrow, so the arrangement of four conductor cables in one level, which is standard at traction current lines, cannot be used. Where four conductors are needed, one approach is to employ a two-level arrangement of conductor cables. Alternatively, in cases of double-tracked railway lines, the overhead line pylons for both driving directions are equipped with cross beams for the traction current system (two conductor cables).
In densely populated areas, where rights of way are rare, it is common to find pylons which carry electric circuits for traction current as well as those for three-phase alternating current. The latter can be 110 kV, 220 kV, or, in some cases, 380 kV three phase AC lines. In such cases, the traction current lines must use insulators which can cope with the maximum peak-to-peak voltage which can occur between the lines.
Traction current lines are implemented as a rule as single leaders. For the supply of railways with much rail traffic and in particular for the power supply of high speed railway lines such as the German ICE (Inter City Express) trains, conductors of two bundles are used. The traction current lines from the nuclear power station at Neckarwestheim to the traction current switching station at Neckarwestheim, and from the traction current switching station at Neckarwestheim to the central substation in Stuttgart Zazenhausen are implemented as four-bundle conductors.
Traction current lines are always equipped with an earth conductor. In some cases, two earth conductors are used: for example in, Germany, in cases where the traction current line is carried on pylons together with three phase AC, like the line to the nuclear power station at Neckarwestheim. Similarly, in Austria there are some traction current lines equipped with two earth ropes.
Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines that facilitate this movement form a transmission network. This is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution. The combined transmission and distribution network is part of electricity delivery, known as the electrical grid.
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 electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances, televisions, fans and electric lamps into a wall socket. A common source of DC power is a battery cell in a flashlight. The abbreviations AC and DC are often used to mean simply alternating and direct, respectively, as when they modify current or voltage.
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In electrical engineering, single-phase electric power is the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors. A single-phase supply connected to an alternating current electric motor does not produce a rotating magnetic field; single-phase motors need additional circuits for starting, and such motors are uncommon above 10 kW in rating.
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A transmission tower, also known as an electricity pylon or simply a pylon in British English and as a hydro tower in Canadian English, is a tall structure, usually a steel lattice tower, used to support an overhead power line.
An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy across large distances. It consists of one or more uninsulated electrical cables suspended by towers or poles.
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.
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Neckarwestheim Nuclear Power Station is a nuclear power plant in Neckarwestheim, Germany, sometimes abbreviated GKN, operated by EnBW Kernkraft GmbH, a subsidiary of EnBW.
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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.
Single-phase generator is an alternating current electrical generator that produces a single, continuously alternating voltage. Single-phase generators can be used to generate power in single-phase electric power systems. However, polyphase generators are generally used to deliver power in three-phase distribution system and the current is converted to single-phase near the single-phase loads instead. Therefore, single-phase generators are found in applications that are most often used when the loads being driven are relatively light, and not connected to a three-phase distribution, for instance, portable engine-generators. Larger single-phase generators are also used in special applications such as single-phase traction power for railway electrification systems.
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.
