Kathryn Bazley asked 6 days ago
The electrical power is then transferred down the DC power cables and converted back into alternating current by way of an inverter. Electric power enters the system in the form of alternating current – generated, for instance, at a local power station, is up-converted to high-voltage AC using standard AC transformers, and converted into DC power by way of a circuit referred to as a rectifier. Colour charts for Western and Northern Electric phones are easy to find. To begin with, the electric railway needs a power supply that the trains can access at all times. This allows for some over supply and provides for continuity if one substation fails. Since the current may have been switched off to stop an arc or because of a short circuit, it is important that the train does not connect the dead section to the live section by passing over the gap and allowing its busline to bridge the gap.
The other shoes on the same circuit must be isolated while this is done, unless the current is switched off from the whole section – perhaps disabling several other trains. At various points along the line, there will be places where trains can be temporarily isolated electrically from the supply system. You will often see trains with only one pantograph but, on trains which use shoes, there are always several shoes. One notable difference between these and their WE/NE counterparts, is that the switchhooks on AE models were designed in a such a way that it was virtually impossible to hang them up improperly, leaving the phone line open. Figure 6: Diagram showing a 3rd rail DC power supply system and how current rail gaps are provided where the substations feed the line. The amplifier housing also includes a power pack to accept power from the cable TV power supply and provide DC voltage to drive the amplifier modules.
Running a 480 volt motor at 415 volts can lead to decreased performance and efficiency due to the lower voltage supply. In that case, you can omit the car adapter. Rapid devices – which can top up a car battery from empty to 80 per cent in around half an hour – make up just over a quarter of the 1,222 additional devices fitted. It can use either DC (direct current) or AC (alternating current), the former being, for many years, simpler for railway traction purposes, the latter being better over long distances and cheaper to install but, until recently, more complicated to control at train level. Top contact systems with protective covers over them, like the New York Subway (Figure 4), needed radially mounted shoes anyway to allow them to fit under the cover. Figure 4: 3rd rail current collection system on the New York Subway showing the third rail with a wooden cover fitted to reduce the effects of snow and ice. It is an embarrassing nuisance only solved by being pushed onto the third rail by another train or by obtaining special long leads with a plug at one end for the train and shoes at the other end for the third rail.
You’re sure to find one that suits your needs and helps you save time and effort. We time how long it takes for the fault to be detected. The following RCD test video is done by connecting a 10K resistor (24 mA ground fault current) from live to ground. Transmission of power is always along the track by means of an overhead wire or at ground level, using an extra, third rail laid close to the running rails. Normally, each track is fed in each direction towards the next substation. The return circuit is via the running rails back to the substation. The running rails are at earth potential and are connected to the substation. There have to be gaps in the thrid rail where crossovers or junctions are provided. Modern shoe systems have remote lifting facilities. The shoe is suspended from an insulated beam hung between the axleboxes. Most types of top contact shoes simply hang from a beam suspended between the axleboxes of the bogie. Side and bottom contact shoes are spring loaded to provide the necessary contact force. Both systems are provided to allow train testing from the main line or London Underground. The wire is zigzagged relative to the centre line of the track to even the wear on the train’s pantograph as it runs underneath.
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