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Most kinds of high contact shoes merely hold from a beam suspended between the axleboxes of the bogie. Figure 5: Simple diagrams of several types of 3rd rail contact systems. There is also a side contact system. Side and backside contact shoes are spring loaded to offer the necessary contact drive. Side contact is not significantly better than prime contact however at the least it's less exposed. Top contact programs with protective covers over them, like the brand new York Subway (Figure 4), wanted radially mounted shoes anyway to permit them to suit underneath the cowl. It additionally suffers during bad weather, the smallest amount of ice or snow rendering top contact third rail programs nearly unworkable unless costly treatments are carried out. It's a top contact system. Being the simplest, it has drawbacks, not the least of which is that it's exposed to anybody or any factor which might come into contact with it. All shoes want some means of being moved clear of the current rail, normally for emergency functions. You will often see trains with only one pantograph however, on trains which use shoes, there are at all times a number of sneakers.

It can use both DC (direct present) or AC (alternating current), the former being, for a few years, easier for railway traction purposes, the latter being higher over long distances and cheaper to install but, till not too long ago, extra complicated to control at train level. A extra efficient system of AC electrification is known because the auto transformer system. Figure 3: Docklands Light Railway prepare with third rail bottom contact electrification system. Later systems had radially mounted shoes to supply more stable contact by way of lever motion. More modern programs use a single arm pantograph - really just half of the unique form - a neater looking design (picture above). Simple - use the steel rails the wheels run on. The mechanics of power provide wiring is just not as simple because it appears (Figure 1). Hanging a wire over the observe, providing it with present and working trains under it isn't that simple if it is to do the job correctly and last long sufficient to justify the expense of putting in it. This has run in parallel with the development of energy electronics and microprocessors. Within the last 20 years there was a rapid acceleration in railway traction development.

Many installations seen immediately have been first constructed more than one hundred years in the past, some when electric traction was barely out of its diapers, so to talk, and this has had an excellent influence on what is seen at this time. Overhead present collectors use a "pantograph", so referred to as because that was the shape of most of them till about 30 years in the past. AC programs always use overhead wires, DC can use both an overhead wire or a 3rd rail; each are widespread. The wire have to be able to carry the current (several thousand amps), remain consistent with the route, withstand wind (in Hong Kong typhoon winds can attain 200 km/h), extreme chilly and heat and other hostile weather situations. DC overhead wires are usually thicker and, in excessive load cases, double wires are used, as in Hong Kong Mass Transit’s 1500 v DC provide system. That is one among the commonest causes of wires "being down". Figure 12: Russian video of a pantograph being damaged by an overhead wire out of place. A practice transferring at pace with its pantograph hooked over the wire can bring down a number of kilometres of line earlier than it's detected and the practice stopped (Figure 12). Essentially the most refined pantographs have horns which are designed to interrupt off when struck arduous, for instance, by a dropper or catenary assist arm.

The rear automobile is supplied via a 25 kV cable running the size of the practice. This diagram exhibits a DC 3-Rail Traction System with the location of the present rail in relation to the working rails. Bottom contact is finest - you'll be able to cowl successfully a lot of the rail and it is protected from the worst of the chilly weather. An example of a backside contact shoe as used on the Dockland Light Railway line in London is shown in Figure three and in the video (Figure 5). Some prime contact techniques have additionally used spring loading however they're mechanically harder to control due to the hunting action of the bogie and the chance that the sneakers will get trapped underneath the top of the rail and turn it over. Figure 2: A 3rd rail collector shoe on a suburban EMU in London. Both systems are provided to allow train testing from the principle line or London Underground. London Underground is the largest person of the 4-rail system in the world. It must be protected, economical and consumer pleasant. The contact with the overhead wire shouldn't be usually broken however the third rail must be damaged at junctions to permit for the continuity of operating rails.

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