Electric train efficiency

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  • #26
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continuing from post #23 one more thing I want to add and ask at the same time, now a diesel electric locomotive has a large diesel and large modern diesels with electronic fuel systems are having efficiencies up to 30/35% now since the wiring is very short in the locomotive the resistive losses in the wires/rails/substations etc are not present so could it be that if the electricity for an electric train is produced in a power plant that uses thermodynamic cycle which has an average efficiency of 30 to 35% then the diesel electric would win out ? because thinking logically a coal plant producing steam driving a turbine which drives a generator have roughly the same energy efficiency than a large diesel running at constant rpm turning a generator the only difference being that in the diesel the electricity can be used on the spot.

You are ignoring the regeneration capability of electric trains, the diesel electrics throw all that kinetic away when they decelerate, that makes an enormous difference.
 
  • #27
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but isn't regeneration only used for AC trains? At least my local older DC trains have large banks of resistors that dump the engine braking current as heat in the environment.
Also regenerative braking might only be worthwhile for urban trains like metro and where the stops are frequent for long lines and freight trains that stop once in a large distance and also switch off the engine before stopping so they use inertia to move the final distance to the stop in the end.
 
  • #28
jim hardy
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Also regenerative braking might only be worthwhile for urban trains like metro and where the stops are frequent for long lines and freight trains that stop once in a large distance and also switch off the engine before stopping so they use inertia to move the final distance to the stop in the end.

Nothing is ever so simple as it sounds at first.
In the old diesels i used to ride
there are separate handles for engine brakes and train brakes.
Engineer uses train brakes a lot when slowing for curves or approaching a stop
in order to keep the train stretched taut
so that when he accelerates again the slack in all those car couplers doesn't "crack the whip" and deliver a jolt to the last few cars.
The locomotive was actually pulling fairly hard as the train rolled to a stop and he'd idle the engine only after it came to rest..

Point being, regenerative braking would seem to me of a lot more benefit at the individual car level rather than the locomotive.
Smaller individually powered cars as on commuter trains seem a natural application...

caveat: it's been over fifty years since i was in a locomotive.
Those are fond memories -
many locomotives weren't even equipped with a speedometer.
The old timey engineer and fiireman pulled out their Hamilton twenty-three jewel railroad pocket watches
counted how many seconds it took for a number of telegraph poles to go by the window.
did the arithmetic in their head; announced the speed together and never differed by more than 1 mph.

old jim
 
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  • #29
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A budding poet - old jim is:

"Nothing is ever so simple
as it sounds at first.
In the old diesels i used to ride
there are separate handles
for engine brakes and train brakes.
Engineer uses train brakes a lot
when slowing for curves or approaching a stop
in order to keep the train stretched taut"
 
  • #30
jim hardy
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:doh::doh:

i didnt even notice the rhyme. Was just trying to keep one thought per line....
 
  • #31
jim hardy
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WTHeck ? Quadruple post ?

and it deleted 3 of them with one blow..
 

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