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The contact strips of the pantograph are supported by a lightweight transverse frame which has "horns" at every finish. These particular horns have a small air stress tube connected which, if the stress is misplaced, will cause the pan to lower mechanically and so cut back the possible wire harm. The subsections may be joined by means of special excessive velocity section switches. On strains geared up with AC overhead wires, special precautions are taken to reduce interference in communications cables. The French TGV (High Speed Train) formation has a power automotive at every finish of the prepare but only runs with one pantograph raised under the excessive velocity 25 kV AC lines. The rear automobile is supplied by means of a 25 kV cable running the size of the train. A couple of pantograph on a train can cause a similar problem when the main pantograph head units up a wave in the wire and the rear head can’t stay involved. To realize this, the provision sub-station transformer is supplied with a centre tap secondary winding at 50 kV (set to 55 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 monitor. Figure 9: To scale back the arcing at a impartial part within the overhead catenary, some systems use track magnets to automatically switch off the facility on the train on the strategy to the neutral section. Figure 8: Insulated neutral part in an overhead line. A second set of magnets restores the power immediately after the impartial part has been passed. Each subsection is remoted from its neighbour by a bit insulator in the overhead contact as shown in this picture beneath. These are turned downwards to reduce the danger of the pantograph being hooked excessive of the contact wire as the prepare strikes along. In operating terms, the third rail is awkward because of the larger risk of it being touched at floor stage. Figure 12: Russian video of a pantograph being broken by an overhead wire out of place. The contact wire is grooved to permit a clip to be fixed on the top aspect (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 form little loops. The wire have to be ready to hold the present (a number of thousand amps), stay consistent with the route, withstand wind (in Hong Kong typhoon winds can attain 200 km/h), excessive cold and heat and different hostile weather conditions. DC overhead wires are normally thicker and, in extreme load circumstances, double wires are used, as in Hong Kong Mass Transit’s 1500 v DC supply system. Pantographs are easy when it comes to isolation - you simply decrease the pan to lose the facility supply to the car. The mechanics of power provide wiring is not as simple because it looks (Figure 1). Hanging a wire over the monitor, providing it with current and working trains below it isn't that straightforward if it is to do the job properly and last long enough to justify the expense of putting in it. Broadly speaking, the upper speeds, the extra complex the "stitching", though a easy catenary will usually suffice if the support posts are close enough collectively on a excessive pace route.

Other than solely requiring a easy control system for the motors, the smaller measurement of city operations meant that trains have been often lighter and needed much less energy. In cities similar to London, New York City and Boston, the same trains run beneath overhead wires for part of the journey and use third rail for the remainder. Careful preparation of earthing safety in constructions and tunnels is an essential part of the railway design course of and is uncared for at one’s peril. Singapore, for example, has banned its use outside of tunnels. More modern methods use a single arm pantograph - actually just half of the original form - a neater trying design (photo above). The upper the pace, the tougher the upkeep of good contact. For the reason that pantograph is often the only point energy contact for the locomotive or energy car, it should maintain good contact underneath all running situations. An electric arc occurs with each bounce and a pan and wire will quickly each grow to be worn by way of underneath such circumstances. Each size is overlapped by its neighbour to make sure a smooth passage for the "pan".