Hands-on Exercise: Burn up A Motor! > 자유게시판

These were used for current collection on low pace overhead techniques and had been frequent on trams or streetcars however they are actually obsolete. The commonest material for electrical wire is copper and aluminum, these usually are not the very best conductors nonetheless they are ample and low price. Pantographs are straightforward by way of isolation - you just decrease the pan to lose the power supply to the vehicle. Figure 11: A schematic showing the arrangements for 25kV AC electrification techniques utilizing booster transformers (higher drawing) and the auto transformer system (decrease drawing). To realize this, the supply sub-station transformer is provided with a centre tap secondary winding at 50 kV (set to 55 kV for the utmost limit of contact wire voltage of 27.5 kV). Heat breaks down all types of insulation finally, and in a motor winding when the insulation will get weak enough two wires side by side will brief, this causes and arc and the system burns out. The contact wire is grooved to allow a clip to be fastened on the highest aspect (Figure 7). The clip is used to attach the dropper wire.

A train shifting at speed with its pantograph hooked over the wire can carry down several kilometres of line earlier than it's detected and the practice stopped (Figure 12). Essentially the most refined pantographs have horns that are designed to break off when struck hard, for example, what is electric cable by a dropper or catenary support arm. This was overcome by putting substations at close intervals - each three or four kilometres at first, these days two or three on a 750 volt system - in contrast with every 20 kilometres or so for a 25 kV AC line. 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. The wire have to be ready to hold the current (a number of thousand amps), stay according to the route, withstand wind (in Hong Kong typhoon winds can reach 200 km/h), extreme cold and heat and other hostile weather circumstances.

It additionally means that, if trains are stopped and need to be evacuated, the current needs to be turned off before passengers may be allowed to wander the track. Although third rail is taken into account a suburban or metro railway system, 750 volt DC third rail supply has been used extensively over southern England and trains using it run regularly up to 145 km/h. In cities resembling London, New York City and Boston, the identical trains run under overhead wires for part of the journey and use third rail for the remainder. Simple - use the steel rails the wheels run on. 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. 25 kV and the feeder wire at -25 kV thus the voltage in between these circuits is 50 kV but to ground is 25 kV. Provided precautions are taken to prevent the voltage getting too excessive above the zero of the ground, it really works very well and has completed so for the final century.

This was well understood within the late nineteenth Century and was one of the reasons why London’s Underground railways adopted a totally insulated DC system with a separate unfavourable return rail in addition to a constructive rail - the four-rail system. It has been discovered to carry out properly at speeds as much as 125 m/hr (200 km/hr). High speeds worsen the problem. The French TGV (High Speed Train) formation has a energy car at every finish of the prepare however solely runs with one pantograph raised beneath the high velocity 25 kV AC lines. The contact strips of the pantograph are supported by a lightweight transverse frame which has "horns" at every finish. The tension of the wire is maintained by weights suspended at every finish of its length. The weights and pulley system is designed to maintain contact wire tension. Gold is usually used involved areas as a result of this point within the system is more exposed to corrosion and has extra potential for oxidization. Some train companies operate over lines utilizing a couple of kind of current. Multiple pantograph on a prepare may cause a similar problem when the main pantograph head sets up a wave in the wire and the rear head can’t keep involved.