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  Railway electrification system - Wikipedia, the free encyclopedia 

  http://en.wikipedia.org/wiki/Railway_electrification_system

  Most electrification systems use overhead wires, but third rail is an option up to about 1200 V. While use of a third rail does not require the use of DC, in practice all third-rail systems use DC because ... it can carry 41% more power than an AC system operating at the same peak voltage. Third rail is more compact than overhead wires and can be used in smaller-diameter tunnels, an important factor for subway systems. Third rail systems can be designed to use top contact, side contact, or bottom contact. Top contact is less safe, as the live rail is exposed to people treading on the rail unless an insulating hood is provided. Side- and bottom-contact third rail can easily have safety shields incorporated, carried by the rail itself. Uncovered top-contact third rails are vulnerable to disruption caused by ice, snow, and fallen leaves. DC systems are limited to relatively low voltages, and this can limit the size and speed of trains and the amount of air-conditioning the trains can provide.   [More...] [Less...]

  First added: 23 July 2008, by: Laura Cage  [Report as spam]

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  Tags:  ets, rail, traction, wikipedia