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Most forms of prime contact sneakers simply dangle from a beam suspended between the axleboxes of the bogie. Figure 5: Simple diagrams of various kinds of third rail contact systems. There can also be a facet contact system. Side and bottom contact footwear are spring loaded to provide the necessary contact pressure. Side contact is not significantly better than prime contact however a minimum of it is less exposed. Top contact techniques with protecting covers over them, like the new York Subway (Figure 4), wanted radially mounted shoes anyway to permit them to fit underneath the cowl. It also suffers during bad weather, the smallest quantity of ice or snow rendering prime contact third rail systems virtually unworkable until expensive remedies are carried out. It is a high contact system. Being the best, it has drawbacks, not the least of which is that it is exposed to anybody or any factor which might come into contact with it. All shoes need some way of being moved clear of the present rail, usually for emergency purposes. You will usually see trains with just one pantograph but, on trains which use shoes, there are all the time a number of footwear.

It might use either DC (direct current) or AC (alternating present), the previous being, for a few years, simpler for railway traction purposes, the latter being higher over long distances and cheaper to install but, until lately, more complicated to control at train stage. A extra environment friendly system of AC electrification is known because the auto transformer system. Figure 3: Docklands Light Railway train with 3rd rail backside contact electrification system. Later techniques had radially mounted footwear to provide more stable contact through lever action. More modern methods use a single arm pantograph - really simply half of the unique form - a neater looking design (photograph above). Simple - use the steel rails the wheels run on. The mechanics of energy provide wiring will not be as simple because it appears to be like (Figure 1). Hanging a wire over the monitor, offering it with present and running trains beneath it is not that simple if it is to do the job properly and final long enough to justify the expense of putting in it. This has run in parallel with the event of energy electronics and microprocessors. In the final 20 years there has been a rapid acceleration in railway traction development.

Many installations seen today had been first built greater than a hundred years ago, some when electric traction was barely out of its diapers, so to talk, and this has had a fantastic affect on what is seen at this time. Overhead present collectors use a "pantograph", so called because that was the shape of most of them till about 30 years ago. AC techniques at all times use overhead wires, DC can use either an overhead wire or a 3rd rail; each are common. The wire must be ready to carry the current (several thousand amps), remain in step with the route, withstand wind (in Hong Kong typhoon winds can reach 200 km/h), excessive chilly and heat and different hostile weather circumstances. DC overhead wires are often thicker and, in extreme load instances, double wires are used, as in Hong Kong Mass Transit’s 1500 v DC provide system. This is one in all the most common causes of wires "being down". Figure 12: Russian video of a pantograph being broken by an overhead wire out of position. A train shifting at speed with its pantograph hooked over the wire can carry down several kilometres of line earlier than it's detected and the practice stopped (Figure 12). Probably the most sophisticated pantographs have horns which are designed to interrupt off when struck exhausting, for instance, by a dropper or catenary assist arm.

The rear automotive is equipped by a 25 kV cable working the size of the prepare. This diagram reveals a DC 3-Rail Traction System with the placement of the present rail in relation to the operating rails. Bottom contact is greatest - you can cowl successfully most of the rail and it's 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 proven in Figure three and in the video (Figure 5). Some high contact techniques have additionally used spring loading however they are mechanically more difficult to manage due to the searching motion of the bogie and the danger that the shoes will get trapped beneath 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 offered to permit train testing from the main line or London Underground. London Underground is the most important consumer of the 4-rail system on this planet. It should be protected, economical and consumer pleasant. The contact with the overhead wire is just not usually damaged but the third rail have to be broken at junctions to permit for the continuity of running rails.

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