Pantograph (rail)
Railroad and rapid transit vehicles that are electrically powered, use one of three overhead collector technologies, of which the pantograph is the most popular.
Third rail
[edit | edit source]Traditional subways did not use an overhead electrical collector, they used a third rail. The third rail carried an electrical charge. Each vehicle in a trainset haw a probe that slides along the third rail. The third rail is about 40 cm from the driving rail, which limits the voltage. Pantographs connect with a wire above the vehicle. This is safer for people on the ground, as it makes it harder to touch both the live rail and a neutral rail. It also means that a higher voltage can be used, without any risk of electrical arcs.
Bow collector
[edit | edit source]The Bow collector is named after the bow used in archery. The arms of the bow keep tension on the electrical connection.
Trolley Pole
[edit | edit source]The trolley pole has a pulley, at the top of a long, spring loaded pole. In addition to up and down motion, the trolley pole is capable of some left and right motion -- necessary when the trolley rounds a curve. If the pulley jumps out of the caternary the driver has to go outside, and use an insulated wire that hangs from the tip of the pole, to guide it back onto the caternary.
The pantograp method
[edit | edit source]The pantograph got its name from a vague resemblance to the true pantograph, a mechanical device where the user's pen is connected, through a series of spring-loaded arms, to a second pen. When in proper workng order, it allows a writerto make a second copy of the document. On a eletrically powered vehicle spring loaded arms press a bar agains the caternary. Unlike with vehicle that use a trolley pole to take their power from a caternary, the caternary has to be laid out with a slight zig-zag. Otherwise it would wear a groove in the pantograph.
References
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