- #1
FOIWATER
Gold Member
- 434
- 12
Hi all:
My question is regarding why electric alternators, dynamic retarding machines, or any rotating source of voltage becomes loaded down when a load is provided across it. I of course understand it in terms of energy, that the load is consuming the voltage that is produced.
But I'm looking for a purely electrical explanation..
I work on a diesel electric fleet of komatsu mining equipment..
When an engine becomes weak, the controller backs off field excitation for the alternator, so it decreases it's output and becomes easier for the engine to rotate, They do this so the engine never stalls out, even when it becomes weak.
So I was wondering HOW reducing excitation, and ultimately the output of the alternator, makes the alternator easier to rotate. Why is there a physical resistance for it to turn as it is increasingly loaded?
I know this is simple and I should know it, but I do not.
I want to reference counter emf in a generator, and say that the more voltage is generates, the more counter emf it generates as well, and somehow reference that to physical work required... any help appreciated
PS: I know already that one could say, "well it of course requires more input if you expect a greater output to feed more loads..." or "compare it to a mechanical load, the more load the harder to turn..."
But I'm really looking for electrical explanations here, and ones that properly illustrate what's happening with reference to induced voltages, and actual loading
let me try and talk myself through it:
the engine rotates the alternator.
the static exciter excites the field.
output is produced in the alternator, due to the fact the conductor is cut by moving lines of flux of the rotating field (rotating field alternator)
the output is a function of the induced voltage, which is a function of the field excitation from the exciter, and the rotational SPEED of engine.
as the generator is loaded, current flows to the loads, voltage is dropped across them due to their resistance.
OK I'm stuck here... like... if the generator wasn't capable of producing enough voltage to power the loads, than you would assume it would just simply...not power them sufficiently? but I don't understand why it becomes harder to turn... :(
My question is regarding why electric alternators, dynamic retarding machines, or any rotating source of voltage becomes loaded down when a load is provided across it. I of course understand it in terms of energy, that the load is consuming the voltage that is produced.
But I'm looking for a purely electrical explanation..
I work on a diesel electric fleet of komatsu mining equipment..
When an engine becomes weak, the controller backs off field excitation for the alternator, so it decreases it's output and becomes easier for the engine to rotate, They do this so the engine never stalls out, even when it becomes weak.
So I was wondering HOW reducing excitation, and ultimately the output of the alternator, makes the alternator easier to rotate. Why is there a physical resistance for it to turn as it is increasingly loaded?
I know this is simple and I should know it, but I do not.
I want to reference counter emf in a generator, and say that the more voltage is generates, the more counter emf it generates as well, and somehow reference that to physical work required... any help appreciated
PS: I know already that one could say, "well it of course requires more input if you expect a greater output to feed more loads..." or "compare it to a mechanical load, the more load the harder to turn..."
But I'm really looking for electrical explanations here, and ones that properly illustrate what's happening with reference to induced voltages, and actual loading
let me try and talk myself through it:
the engine rotates the alternator.
the static exciter excites the field.
output is produced in the alternator, due to the fact the conductor is cut by moving lines of flux of the rotating field (rotating field alternator)
the output is a function of the induced voltage, which is a function of the field excitation from the exciter, and the rotational SPEED of engine.
as the generator is loaded, current flows to the loads, voltage is dropped across them due to their resistance.
OK I'm stuck here... like... if the generator wasn't capable of producing enough voltage to power the loads, than you would assume it would just simply...not power them sufficiently? but I don't understand why it becomes harder to turn... :(
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