- Traction power network
original research=August 2008
A traction power network is an electricity grid for the supply of electrified railroads. The installation of separate traction power network generally is only done if the railway in question uses
alternating currentwith a frequency lower than that of the national grid, such as in Germany, Austriaand Switzerland.
Alternatively, the three-phase alternating current of the power grid can be converted in substations by rotary transformers or static inverters into the voltage and type of current required by the trains. For railways which run on
direct current, this method is always used, as well as for railways which run on single phase AC current of decreased frequency, as in Mecklenburg-Western Pomerania, Saxony-Anhalt, Norwayand Sweden. In these areas there are no traction current networks.
Power schemes for traction apart from industrial power schmes always have historic roots. There is no reason today to apply different frequencies or current types than for transmission and for industrial usage. However, the advantage with DC current traction was the easier transmission with single copper wires to the feeder points. The advantage with AC current traction is the easier transmission over long distances to the feeder points. Beyond these parameters and securing former investment no evidence exists to stay with different current schemes in networks.
traction currentlines are used when railways are supplied with low frequency alternating current. The traction current supply line is connected to substations along the line of the railway and is usually run separately from the overhead catenary wirefrom which the locomotives are fed.
In countries in which the electric trains run with direct current or with single phase AC 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
pylonsabove 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 right of ways 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
insulatorsfor 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.
Around the World
The Mariazeller railway in
Lower Austriaoperates on single phase AC at a 25 Hz utility frequency. The railway 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 catenary wire.
Germanysingle conductors are usually used for traction current lines, but for the ICE train, two bundle conductors are used. The traction current supply lines from the nuclear power station Neckarwestheimto the traction current switching station at Neckarwestheimand from there to the central substationin Stuttgart, Zazenhausenare implemented as a four-bundle conductor circuit.
Sweden, Norwayand some areas of the former German Democratic Republicthree phase AC-current is converted into single phase AC current with a frequency of 16,7 cycles per second at the substations. In these regions there are no traction current lines, except extra lines along the railways to increase supply for heavily used railways.
In the Republic of
South Africathere are extensive AC and DC traction schemes, including 50 kV and 25 kV AC single phase systems. Electrification in Natal was stimulated by the takeover of the South African Railways' system by the Electricity Supply Commission (now Eskom) based on the Colensopower station.
United Kingdomthe British RailSouthern Region 750 V DC electrification system is supplied with power from an extensive 33 kV power distribution network.Fact|date=November 2007
Areas with traction power networks
Germany(except Mecklenburg-Western Pomerania and Saxony-Anhalt), total length 7959km
Austria(separate traction power network for the Mariazeller Bahn)
* USA (in New York and Washington DC area for railway lines running with single phase 25 Hz AC)
Melbourne, Australia(dedicated high voltage transmission wires between former Newport A Power Station and traction substations)
Traction current converter plant
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