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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 pressure tube connected which, if the strain is lost, will trigger the pan to decrease robotically and so reduce the attainable wire damage. The subsections could be joined via particular excessive velocity section switches. On lines equipped with AC overhead wires, particular precautions are taken to reduce interference in communications cables. The French TGV (High Speed Train) formation has a energy car at each finish of the prepare but solely runs with one pantograph raised under the excessive speed 25 kV AC lines. The rear automobile is supplied by means of a 25 kV cable operating the size of the train. Multiple pantograph on a practice can cause a similar downside when the main pantograph head sets up a wave within the wire and the rear head can’t keep in contact. To attain this, the supply sub-station transformer is supplied with a centre tap secondary winding at 50 kV (set to fifty five kV for the maximum limit of contact wire voltage of 27.5 kV).

The wire is zigzagged relative to the centre line of the observe to even the wear on the prepare's pantograph as it runs beneath. The contact wire has to be held in tension horizontally and pulled laterally to negotiate curves in the monitor. Figure 9: To cut back the arcing at a impartial part within the overhead catenary, some methods use observe magnets to routinely switch off the ability on the prepare on the approach to the impartial section. Figure 8: Insulated impartial part in an overhead line. A second set of magnets restores the power immediately after the impartial part has been handed. Each subsection is isolated from its neighbour by a bit insulator in the overhead contact as proven on this picture beneath. These are turned downwards to reduce the chance of the pantograph being hooked over the top of the contact wire because the practice moves along. In working terms, the third rail is awkward due to the greater risk of it being touched at ground degree. 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 side (Figure 7). The clip is used to attach the dropper wire.

It could cause the dropper wires, from which the contact wire is hung, to "kink" and kind little loops. The wire must be ready to carry the present (several 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 often thicker and, in excessive load instances, double wires are used, as in Hong Kong Mass Transit’s 1500 v DC supply system. Pantographs are straightforward when it comes to isolation - you simply decrease the pan to lose the ability provide to the car. The mechanics of energy supply wiring is not as simple because it seems (Figure 1). Hanging a wire over the track, offering it with present and working trains underneath it isn't that straightforward whether it is to do the job correctly and final long enough to justify the expense of installing it. Broadly speaking, the upper speeds, the extra complicated the "stitching", though a easy catenary will normally suffice if the support posts are close enough collectively on a excessive velocity route.

Other than only requiring a simple control system for the motors, the smaller dimension of urban operations meant that trains had been often lighter and needed much less energy. In cities reminiscent of 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 protection in structures and tunnels is an essential a part of the railway design course of and is uncared for at one’s peril. Singapore, for instance, has banned its use outside of tunnels. More modern methods use a single arm pantograph - really just half of the original form - a neater looking design (picture above). The higher the pace, the tougher the maintenance of excellent contact. Because the pantograph is often the one point energy contact for the locomotive or power automobile, it should maintain good contact under all running circumstances. An electric arc happens with every bounce and a pan and wire will soon both turn into worn by underneath such conditions. Each size is overlapped by its neighbour to ensure a smooth passage for the "pan".