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The contact strips of the pantograph are supported by a lightweight transverse body which has "horns" at every end. These particular horns have a small air strain tube connected which, if the strain is lost, will cause the pan to decrease robotically and so cut back the possible wire harm. The subsections can be joined via special excessive velocity part switches. On lines outfitted with AC overhead wires, special precautions are taken to reduce interference in communications cables. The French TGV (High Speed Train) formation has a energy car at every end of the train but only runs with one pantograph raised under the high speed 25 kV AC lines. The rear automobile is equipped by way of a 25 kV cable operating the length of the train. More than one pantograph on a prepare could cause an analogous downside when the main pantograph head sets up a wave within the wire and the rear head can’t stay in touch. To attain this, the provision sub-station transformer is provided with a centre tap secondary winding at 50 kV (set to fifty five kV for the maximum restrict of contact wire voltage of 27.5 kV).

The wire is zigzagged relative to the centre line of the track to even the wear on the prepare's pantograph as it runs underneath. The contact wire must be held in tension horizontally and pulled laterally to negotiate curves in the observe. Figure 9: To scale back the arcing at a neutral section within the overhead catenary, some systems use observe magnets to robotically swap off the ability on the prepare on the method to the neutral section. Figure 8: Insulated neutral part in an overhead line. A second set of magnets restores the facility immediately after the neutral section has been handed. Each subsection is remoted from its neighbour by a piece insulator within the overhead contact as shown in this picture under. These are turned downwards to scale back the risk of the pantograph being hooked excessive of the contact wire because the prepare strikes along. In operating terms, the third rail is awkward due to the better threat of it being touched at floor level. Figure 12: Russian video of a pantograph being broken by an overhead wire out of position. The contact wire is grooved to allow a clip to be fastened on the top side (Figure 7). The clip is used to attach the dropper wire.

It can cause the dropper wires, from which the contact wire is hung, to "kink" and type little loops. The wire must be ready to carry the present (several thousand amps), stay in step with the route, withstand wind (in Hong Kong typhoon winds can reach 200 km/h), excessive chilly and heat and other hostile weather circumstances. DC overhead wires are often thicker and, in extreme load circumstances, double wires are used, as in Hong Kong Mass Transit’s 1500 v DC provide system. Pantographs are straightforward by way of isolation - you just lower the pan to lose the facility provide to the automobile. The mechanics of energy supply wiring will not be as simple as it seems (Figure 1). Hanging a wire over the track, providing it with present and operating trains beneath it's not that straightforward whether it is to do the job properly and final lengthy sufficient to justify the expense of putting in it. Broadly speaking, the higher speeds, the more complex the "stitching", though a simple catenary will often suffice if the help posts are close enough collectively on a excessive speed route.

Aside from only requiring a easy management system for the motors, the smaller dimension of city operations meant that trains had been normally lighter and wanted less power. In cities equivalent to London, New York City and Boston, the same trains run below overhead wires for part of the journey and use third rail for the remainder. Careful preparation of earthing safety in structures and tunnels is a vital part of the railway design course of and is uncared for at one’s peril. Singapore, for instance, has banned its use exterior of tunnels. More modern programs use a single arm pantograph - actually just half of the unique shape - a neater looking design (picture above). The upper the velocity, the more difficult the maintenance of good contact. Since the pantograph is often the one point power contact for the locomotive or energy automobile, it must maintain good contact below all running situations. An electric arc occurs with every bounce and a pan and wire will soon both change into worn by underneath such situations. Each length is overlapped by its neighbour to make sure a easy passage for the "pan".