Basic Working of Electric Locomotives Explained
These days we hardly find any steam locomotive running carrying bogies. The first electric locomotive was built by Robert Davidson way back in 1837. After that the electric
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Image credit: evworld.com
locomotive gained more and more importance over the traditional steam locomotives and today we hardly find steam locos in museums. The reason behind this is the several advantages that a electric loco has got over the steam loco. However the working of an electric loco is not that simple. Here I will try to explain it as simply as I can.
There will be two parts of this article:
1) How does an electrical locomotive run?
2) How does it stop?
How does an electrical locomotive run?
Motors used: The motors used in an electric locomotive are Direct Current Series Motors. Now why DE SE motors? It is because of the load torque curve of a train. The torque requirement in propulsion of a train goes on decreasing with the increase in the speed. DC SE motors on account of their construction have a torque speed characteristic that exactly matches the load requirements and hence we use DC SE motors in electrical locos. DC SE motors are basically used in urban and sub-urban areas but single phase induction motors can also be used where sudden acceleration is not required and the train run is very long.
Series – Parallel method: In locomotion, a number of DC SE motors are used in different combinations. During the initial acceleration period, both the DC SE motors are connected in series with each other with some heavy resistance also present in series combination. This resistance is basically used to limit the heavy starting currents, till the back EMF develops (back EMF is proportional to speed of motor). Then as the train gains speed, this resistance is gradually cut out and the motor gains speed. Now as the current in the series circuit reach the rated value,(when this happens, the motors approach almost half of their individual capacity) the current limiting resistance is reinserted into the circuit. Then the series combination is gradually converted into a parallel combination. Time period for which the motors should run as a series combination and as a parallel combination is determined by the run, run time between stations and acceleration of the train. After the motors are in to parallel combination the loco again accelerates to its maximum speed. Implementation of this system fetches us a considerable amount of savings in energy consumption without compromise with the acceleration and maximum speed.
Next, I will be writing about different methods used for braking.
Image credit: evworld.com
locomotive gained more and more importance over the traditional steam locomotives and today we hardly find steam locos in museums. The reason behind this is the several advantages that a electric loco has got over the steam loco. However the working of an electric loco is not that simple. Here I will try to explain it as simply as I can.
There will be two parts of this article:
1) How does an electrical locomotive run?
2) How does it stop?
How does an electrical locomotive run?
Motors used: The motors used in an electric locomotive are Direct Current Series Motors. Now why DE SE motors? It is because of the load torque curve of a train. The torque requirement in propulsion of a train goes on decreasing with the increase in the speed. DC SE motors on account of their construction have a torque speed characteristic that exactly matches the load requirements and hence we use DC SE motors in electrical locos. DC SE motors are basically used in urban and sub-urban areas but single phase induction motors can also be used where sudden acceleration is not required and the train run is very long.
Series – Parallel method: In locomotion, a number of DC SE motors are used in different combinations. During the initial acceleration period, both the DC SE motors are connected in series with each other with some heavy resistance also present in series combination. This resistance is basically used to limit the heavy starting currents, till the back EMF develops (back EMF is proportional to speed of motor). Then as the train gains speed, this resistance is gradually cut out and the motor gains speed. Now as the current in the series circuit reach the rated value,(when this happens, the motors approach almost half of their individual capacity) the current limiting resistance is reinserted into the circuit. Then the series combination is gradually converted into a parallel combination. Time period for which the motors should run as a series combination and as a parallel combination is determined by the run, run time between stations and acceleration of the train. After the motors are in to parallel combination the loco again accelerates to its maximum speed. Implementation of this system fetches us a considerable amount of savings in energy consumption without compromise with the acceleration and maximum speed.
Next, I will be writing about different methods used for braking.
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