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Each size is overlapped by its neighbour to make sure a smooth passage for the "pan". Each subsection is remoted from its neighbour by a bit insulator in the overhead contact as shown on this picture beneath. The weights and pulley system is designed to keep up contact wire tension. The contact wire has to be held in tension horizontally and pulled laterally to negotiate curves within the monitor. The contact wire tension might be within the area of two tonnes. The contact strips of the pantograph are supported by a lightweight transverse frame which has "horns" at each end. In fact there are exceptions and we are going to see a few of them later. An electric arc occurs with each bounce and a pan and wire will quickly each grow to be worn through beneath such conditions. As AC is easier to transmit over lengthy distances, it is a perfect medium for electric railways. Some train companies operate over traces using multiple type of present. This is certainly one of the commonest causes of wires "being down".

DC overhead wires are usually thicker and, in extreme load circumstances, double wires are used, as in Hong Kong Mass Transit’s 1500 v DC provide system. In cities similar to London, New York City and Boston, the same trains run beneath overhead wires for a part of the journey and use third rail for the remainder. Figure 9: To reduce the arcing at a impartial part within the overhead catenary, some techniques use monitor magnets to automatically switch off the facility on the practice on the method to the impartial part. The wire is zigzagged relative to the centre line of the observe to even the put on on the train's pantograph because it runs beneath. The French TGV (High Speed Train) formation has a power automobile at every end of the prepare but only runs with one pantograph raised beneath the high velocity 25 kV AC strains. The rear automobile is supplied by way of a 25 kV cable working the size of the train. The impact of this arrangement is to reduce the noise ranges within the communications cable and ensure the voltages stay at a protected level.

In Europe, some locomotives are equipped to function below 4 voltages - 25 kV AC, 15 kV AC, what is electric cable 3,000 V DC and 1,500 V DC. These are positioned on masts at intervals along the route. The return conductor is connected to the running rail at intervals to parallel the return cable and rails. They're related to the feeder station by a return conductor cable hung from the masts so that it is roughly the same distance from the observe as the overhead line. There has to be an entire circuit, from the source of the power out to the consuming merchandise (light bulb, cooking stove or train) and back to the supply, so a return conductor is needed for our railway. What about the electrical return? If a communications cable is laid alongside rails carrying the return current of the overhead line supply, it may well have unequal voltages induced in it. It can be summarised merely as AC for long distance and DC for brief distance. After all, it wanted a heavier transmission medium, a 3rd rail or a thick wire, to hold the power and it lost a fair amount of voltage as the gap between supply connections increased.

Provided precautions are taken to stop the voltage getting too high above the zero of the ground, it works very well and has carried out so for the last century. Broadly speaking, the higher speeds, the more complex the "stitching", though a easy catenary will normally suffice if the help posts are close sufficient collectively on a high velocity route. The mechanics of energy provide wiring shouldn't be as simple because it seems to be (Figure 1). Hanging a wire over the monitor, providing it with present and running trains below it isn't that straightforward whether it is to do the job properly and last lengthy sufficient to justify the expense of installing it. Figure 11: A schematic exhibiting the arrangements for 25kV AC electrification systems using booster transformers (upper drawing) and the auto transformer system (lower drawing). Figure 7: Overhead contact wire displaying the grooves added to supply for the dropper clips. Figure 12: Russian video of a pantograph being broken by an overhead wire out of position. More than one pantograph on a train can cause an analogous problem when the leading pantograph head units up a wave in the wire and the rear head can’t keep involved. Originally, pantographs have been just that, a diamond-formed "pantograph" with the contact head at the top.