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1、Introduction to LocmotiveA locomotive is a railway vehicle that provides the motive power for a train,and has nohy detached from their trains, are known as power cars.Traditionally,locomotive hual their trains. Increasingly common these days in passenger service is push-pull operation,where the loco
2、motive push the trains in one direction and are controled from a control cab at the opposite end of the train in the other.Beniefits of locomotivesThere are many reasons why the motive power for trains has been traditonally isolated in a locmotive,rather than is self-propelled vehicles.these include
3、:Ease of maintenance it is easier to maintain one locomotive than many self-propelled cars.Safety it is often safer to locate the trains power system away from passenger. This was particularly the case for the steam locomtive,but still has some relevance.Easy replacement of motive power should the l
4、ocomotive break down, it is easy to replace it with a new one . Failure of the motive power unit does not require taking the whoole train out of service.Efficiency idle trains do not waste expensive motive power resources. Separate locomotives mean that the costly motive power assets can be moved ar
5、ound as needed.Obsolescence cycles separating the motive power from the payload-hauling cars means that either can be replaced without affecting the other. At some times, locomotive have become obsolete when their cars are not, or vice versa.Electric LocomotivesThe electric locomotive is supplied ex
6、ternally with electric power, either through an overhead pickup or through a third-rail. While the cost of electrifying track is rather high, electric trains and locomotives are significantly cheaper to run than diesel ones, and are capable of superior acceleration as well as regenerative braking, m
7、aking them ideal for passenger service in densely populated areas. Almost all high speed train systems(e.g.IEC,TGV, bullet train) use electric power, because the power needed for such performance is not easily carried on board. Fot example the most powerfu electric locomotives that are used today on
8、 the channel tunnel freight services use 7Mwatts of power.The first known electric locomotive was buit by a Scotsman, Roert Davidson of Aberdeen in 1837 and was powered by galvanic cells.Modern electric locomotive range from small battery-powered machines for use in mines to large main-line locomoti
9、ves of 6,000 horsepower(4.5MW) or more.In reality most modern locomotives are electricaly driven. Pure electric locomotives take their electrical supply from an external source while diesel-electric locomotives carry their own generating station.Main line electric locomotives first appeared at the b
10、eginning of the 20th century.The reason for their introduction was the problem of smoke, especially in tunnlels caused by steam locomotives. In the UK this was the London underground system while in the USA, it was under river tunnles and needs to eliminate smoke in built up areas.Early electric loc
11、omotives all relied on external power sourcing. Once up and running they tend to be reliable and efficint, but the supply infrastructure is a large capital expense that does require ongoing maintenance. For this reason only heavily used lines could justify electrification. For suburban lines the red
12、uction in pollution from steam locomotives was a benefit all were aware oflThe world speed record for a wheeled train was set in 1990 ba a French TGV which reached a speed of 515.3km/h (320mph).While recently designed electrififed railway systems invariably operate on alternating current, many exist
13、ing direct current sytems are still in use e.g. in South Africa,Spain,and the United Kingdom(750v and 1500v); Netherlands(1500v); Belgiu, Italy, Poland (3000 v), and the cites of Mumbia and Chicagio (which will be switched to AC by 2025).Early locomotives came in a variety of forms. Generally they w
14、ere designed to run off the supplied current. so locomotives with a direct current (DC) supply had DC motors while a alterntating current(AC) supplied locomotives with AC motors. AC can be either single or three phase. While the former requies two wire supply, one overhead the other being the track,
15、 three phase require three supply wire.Three phase locomotives therefore had two overhead supplies,the track being the third.DC supplies were either overhead or by means of a track level supply, commonly called the third rail.AC traction motors tended to be smaller than DC motors. This often meant e
16、lectric locomotives with steam engine type cranks. DC motors could be smaller and set up to drive the axles.usually through a gear ,but in some early examples by being part of the axle. Even so, some notable DC electric locomotives had large DC motors driving large driving wheels. One possibility with electric locomotives is that the motor can be used as a generator during braking, feeding electricity back into the supply system;
