An electric locomotive is an engine that is powered by electricity through overhead lines, a third rail, or on-board energy storage. This energy storage can be in the form of a battery or even, as technology advances, a supercapacitor.
Electric locomotives are highly efficient over other types of locomotives; often above 90%!
Locomotives that include on-board fueled prime movers are known as diesel-electric locomotives (when powered by diesel engines) or gas turbine-electric locomotives (when utilizing a turbine). While turbine engines are lighter for the same amount of power produced, they require more specialized maintenance than the traditional two- or four-stroke diesel engine.
A diesel-electric locomotive is equipped with a diesel engine that spins a generator (DC) or alternator (AC) to create electricity. This electricity then powers the heavy electric motors that move the train forward. A diesel-electric locomotive has no mechanical connection between the prime mover and the axles.
Direct Current electric motors are cheaper to construct but have limited overload duration before damage occurs. Alternating Current electric motors are more expensive to construct but have the advantage of taking as much power as the engine can generate - a heavily loaded coal train can pour electricity into its AC motors without fear of overheating.
One of the greatest advantages of electric and diesel-electric propulsion is that the locomotive’s power output is independent of its speed, allowing it to apply full power at a dead stop. A steam locomotive, on the other hand, generates the least amount of useful power when stopped and reaches a maximum power, determined by driver size, boiler pressure, and valve settings, that cannot be altered.
There are three primary types of diesel-electric transmission, each with their own benefits and drawbacks.
DC - This design includes a generator that supplies the DC traction motors through a resistance control system.
AC-DC - With this design, there is an alternator that produces AC current that is rectified to DC and then transferred to the DC traction motors
AC-DC-AC - With powering 3-phase AC traction motors, this modern design has the AC alternator output being rectified to DC and then converted to AC. This system may be slightly more complex than the others, though there are more benefits to doing it this way.
|Powered by electricity transmitted through wires or rail from a stationary powerplant.||Self-contained power generation with no need for transmission wires or expensive third-rail systems.|
|Pantographs on the roof of the locomotive collect power from overhead lines, or special shoes gather current from a third rail.||Conventional diesel-electric locomotives use a diesel-fueled two- or four-stroke engine. Gas turbines may use fuel oil to heat water and create steam to power a turbine.|
|Capacity for immense power output, typically limited by the amount of electricity available and the likelihood of the motors melting down.||Power output limited by the size of the diesel engine, requiring a balance between high output and reliability.|
|Capable of short-term bursts of high acceleration, perfect for stop and go commuter service.||Without the need for wires or third rail, there is greater freedom of movement for a diesel-electric locomotive and less risk of severe weather interrupting service.|
|Single-source pollution allows for easier to implement reduction efforts without requiring an overhaul of rolling stock.||Every locomotive generates pollution, requiring expensive overhauls and even re-engine refits in order to meet more strict emissions standards.|
There are so many different parts and components that make up electric and diesel-electric locomotives. There are advantages and disadvantages to using both engines, though overall these engines are both more modern and have more benefits than using a steam engine. No matter which locomotive you choose, make sure you are prepared!
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