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Most kinds of prime contact sneakers merely hang from a beam suspended between the axleboxes of the bogie. Figure 5: Simple diagrams of different types of 3rd rail contact systems. There can be a side contact system. Side and bottom contact shoes are spring loaded to supply the mandatory contact power. Side contact shouldn't be significantly better than high contact but at least it's less exposed. Top contact systems with protecting covers over them, like the new York Subway (Figure 4), needed radially mounted shoes anyway to allow them to suit underneath the cowl. It also suffers during bad weather, the smallest quantity of ice or snow rendering top contact third rail methods almost unworkable unless expensive remedies are carried out. It is a prime contact system. Being the simplest, it has drawbacks, not the least of which is that it is uncovered to anyone or any thing which might come into contact with it. All footwear want some means of being moved clear of the present rail, normally for emergency functions. You will often see trains with only one pantograph but, on trains which use footwear, there are all the time a number of sneakers.

It could use both DC (direct current) or AC (alternating present), the previous being, for many years, simpler for railway traction functions, the latter being better over long distances and cheaper to install but, till lately, extra difficult to regulate at practice stage. A more environment friendly system of AC electrification is known as the auto transformer system. Figure 3: Docklands Light Railway train with 3rd rail bottom contact electrification system. Later systems had radially mounted sneakers to provide more stable contact by means of lever action. More fashionable systems use a single arm pantograph - really simply half of the unique form - a neater trying design (photograph above). Simple - use the steel rails the wheels run on. The mechanics of energy provide wiring shouldn't be as easy as it appears (Figure 1). Hanging a wire over the monitor, offering it with current and working trains beneath it's not that simple if it is to do the job correctly and final long enough to justify the expense of installing it. This has run in parallel with the development of power electronics and microprocessors. In the final 20 years there was a speedy acceleration in railway traction development.

Many installations seen immediately have been first constructed greater than one hundred years in the past, some when electric traction was barely out of its diapers, so to speak, and this has had an excellent influence on what's seen at present. Overhead present collectors use a "pantograph", so referred to as because that was the form of most of them till about 30 years in the past. AC methods all the time use overhead wires, DC can use both an overhead wire or a 3rd rail; each are common. The wire should be ready to carry the present (several thousand amps), remain in line with the route, withstand wind (in Hong Kong typhoon winds can reach 200 km/h), extreme chilly and heat and other hostile weather circumstances. DC overhead wires are usually thicker and, in extreme load instances, double wires are used, as in Hong Kong Mass Transit’s 1500 v DC provide system. This is certainly one of the most typical causes of wires "being down". Figure 12: Russian video of a pantograph being broken by an overhead wire out of position. A prepare moving at pace with its pantograph hooked over the wire can convey down several kilometres of line earlier than it is detected and the practice stopped (Figure 12). The most subtle pantographs have horns that are designed to interrupt off when struck arduous, for instance, by a dropper or catenary assist arm.

The rear automobile is supplied by a 25 kV cable operating the size of the train. This diagram shows a DC 3-Rail Traction System with the placement of the current rail in relation to the running rails. Bottom contact is greatest - you may cover effectively many of the rail and it is protected from the worst of the chilly weather. An example of a bottom contact shoe as used on the Dockland Light Railway line in London is shown in Figure three and within the video (Figure 5). Some top contact systems have additionally used spring loading however they are mechanically more difficult to manage due to the looking motion of the bogie and the danger that the sneakers will get trapped under the pinnacle of the rail and switch it over. Figure 2: A 3rd rail collector shoe on a suburban EMU in London. Both methods are offered to permit prepare testing from the primary line or London Underground. London Underground is the most important consumer of the 4-rail system in the world. It have to be secure, economical and person pleasant. The contact with the overhead wire just isn't normally damaged but the third rail must be broken at junctions to permit for the continuity of working rails.

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