Traction power network

This article does not cite any sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Traction power network" – news · newspapers · books · scholar · JSTOR (December 2018) (Learn how and when to remove this template message)

A traction network or traction power network is an electricity grid for the supply of

.

Alternatively, the three-phase alternating current of the power grid can be converted in

. In these areas there are no traction current networks.

History

Separate power for traction apart from industrial power has 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 traction was the easier transmission with single copper wires to the feeder points. The advantage with AC 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.

Applications

Dedicated

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

are used.

Around the world

Austria

The

. 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.

Germany

In

are implemented as a four-bundle conductor circuit.

Scandinavia

In

, 50 Hz is used for the main lines (if electrified) and the electricity comes from general suppliers. As such, much simpler equipment than in Sweden and Norway is needed for conversion.

South Africa

In the Republic of

.

United Kingdom

In the

]

Areas with traction power networks

• United Kingdom
• Germany (except Mecklenburg-Western Pomerania and Saxony-Anhalt), total length 7,959 km
• Switzerland
• Mariazeller Bahn
  )
• Central Sweden
• Southern Norway east of Oslo
• Harrisburg, PA running with single phase 25 Hz AC, see also Amtrak's 25 Hz traction power system
  )
• South Africa
• Newport A Power Station
  and traction substations. However these lines are operated with three phase AC)
• Riyadh, Kingdom of Saudi Arabia (Riyadh Metro Networks)

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

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

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

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.

Alternatives to traction current lines

In

former GDR

three phase AC from the public grid is converted into single phase AC with a frequency of 16.7 Hz in substations close to the railways. In these regions there are no traction current lines.

Also in countries in which the electric trains run with direct current or with single phase AC with the frequency of the general power grid, the required conversion of the current is performed in the substations, so that in these countries no traction current lines are needed.

See also

• Third rail
• Traction current converter plant
• Traction powerstation