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]] An electric locomotive is a Locomotive powered by Electric Motor s which draws Current from an overhead wire ( Overhead Lines ), a Third Rail , or an on-board storage device such as a Battery or a Flywheel Energy Storage system. The first known electric locomotive was built by a Scotsman , Robert Davidson of Aberdeen in 1837 and was powered by Galvanic Cell s. Davidson later built a larger locomotive named Galvani which was shown at the Royal Scottish Society Of Arts Exhibition in 1841 . . This locomotive is on display and not currently in service.]]Modern electric locomotives range from small battery-powered machines for use in Mines to large main-line locomotives of 6,000 kW (8,000 horsepower) or more. In reality most modern locomotives are electrically driven. Pure electric locomotives take their electrical supply from an external source while Diesel-electric Locomotive s carry their own generating station. Main line electric locomotives first appeared at the beginning of the 20th Century . The reason for their introduction was the problem of smoke, especially in tunnels caused by steam locomotives. In the UK this was the London Underground system while in the USA , it was under river tunnels and the need to eliminate smoke in built up areas. Early electric locomotives all relied on external power sourcing. Once up and running they tend to be reliable and efficient, but the supply infrastructure is a large capital expense that does require ongoing maintenance. Alternating current or direct current? Early locomotives came in a variety of forms. Generally they were designed to run off the supplied current, so locomotives with a Direct Current (DC) supply had DC motors while Alternating Current (AC) supplied locomotives with AC motors. AC can be either Single or Three Phase . While the former requires two wire supply, one overhead the other being the track, three phase requires three supply wires. 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 Motor s tended to be larger than DC motors. This often meant electric locomotives with Jackshaft s which resembled Steam Engine type Cranks . DC motors could be smaller and set up to drive the Axle s, 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 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; this is called Regenerative Braking . This is not a new idea; it was one reason for the adoption by some railways of 3 phase AC supplies. Regenerative breaking is especially useful in mountainous areas where the locomotive going down would generate much of the supply for a locomotive going up. The Swiss railway uses this system; three modern locomotives heading downwards generate enough power to power a single locomotive on its upward journey. Today all electric locomotives tend to have the traction motors on the Bogie s, close to the axles, although some still have the motor in the body driving the wheels through internal drive shafts. Modern solid state electrical control systems means the motor does not need to match the supply. This means multi-voltage cross border locomotives are now quite common. Drive motors are generally DC, but there are 3 phase drive motors on some locomotives. Efficiency If the locomotive is considered alone, electric engines would seem to be much more efficient than steam or diesel-electric engines. But the efficiency of the locomotive alone does not, in any way, determine the efficiency of the whole electric traction system. This is because the efficiencies of the power plant and transmission system are not taken into account. If these are considered, then electric engines would not seem to be much efficient. Advantages Electric engines are very powerful. Electric motors can produce as much Torque as power is given. As the power supply to the motors is not limited in theory any power is possible. In diesels the power supply to the motors is limited by the amount of electricity the diesel engine can generate. But electric engines draw power from large power plants and they can provide much greater amount of power. In reality as long structural integrity of the engine and the tracks can hold up the power can be increased. This makes electrics suitable for hauling very heavy loads. Electric engines have a better power-to-weight ratio than steam or diesel engines as they pick up energy from an external supply line (overhead wire or third rail) and hence do not need to carry a power generating system as steam or diesel engines need. Thus an electric engine is much lighter than a diesel engine of same power. Hence they can attain very High Speeds . Moreover they can accelerate at a much higher rate. This makes them very much suitable for suburban Commuter Traffic routes with many stops. Another major advantage is that there is less wear and tear due to less number of moving parts in electric engines. The only running parts are the traction motors and the wheels. So they require less time and money for maintenance. Due to their comparatively light weight the tracks do not get worn out fast. Electric engines do not pollute the environment as there is no emission. They reduced the pollution from steam locomotives in suburban lines. For the same reason the only locomotives suitable for underground railways are electrics. Disadvantages The primary disadvantage of electric engines is that they require an external power supply line. Building overhead wire or third rail system is a very expensive work. As most of the existing railway network was built during the steam era, bridges and tunnels weren't made high enough to provide space overhead wires. This makes the work even more complex as such bridges or tunnels are to be reconstructed during electrification. As a result very high initial investment is needed. For this reason only heavily used lines can justify electrification. So, electric engines are limited. They can't go everywhere on the network See also External links |