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How Electric Locomotives (Electric Trains) Work?

What is an Electric Locomotive?

An “Electric Locomotive” is a railway vehicle that can move along rails and push or pull a train attached to it using electric power drawn from an external source, usually from overhead cables or a third rail. 

Electric Locomotives do not have a conventional “engine” in them, but use the electricity collected from the outside source to power traction motors which turn the wheels. 

Types of Electric Locomotives

Electric Locomotives are of three types: Those which can work on 
  • DC (Direct Current), 
  • AC (Alternating Current) or 
  • on both (AC/DC – Bi-current). 
Electric Locomotives, though high on electrical engineering, work on the single principle of drawing current from external sources and then after sufficiently “modifying” it, feed it to the traction motors. The process of “modifying” the raw current drawn from outside into “usage” power includes a complicated process of conversion, reconversion, smoothening and transformation of the current to varying values of frequency, Voltage, Current etc. 

Inside an Electric Locomotive


This involves a bank of many components like transformers, rectifiers, inverters, capacitors, thyristors, compressors and other such paraphernalia, housed within the locomotive body or the “shell”, and there is no central “Engine” or prime mover. 

All this has to be done for optimum performance of the traction motors under different conditions and loads. Bi-Current locomotives work according to the same principles, only they have more equipment packed inside them to enable them to work under both type of currents. Each one the Pantographs are used to collect a specific type of current only. 
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Drawback of Electric Locomotive

Electric locomotives have this major drawback of being totally dependent on the power which has to be supplied for it to run. Any power outage, short circuit or breaking of Overhead Equipment (OHE) will cause trains to come to a standstill. Hence, even on fully electrified routes, diesel locomotives are kept on standby always. And on partly electrified routes, trains are run on diesel under the wire because it is more efficient than switching locomotives.