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So in a 3 phase induction generator with coils for the stator and magnets for on the rotor, I am wondering if the the current induced in the coils would create a magnetic field that would oppose the rotation of the magnets on the rotor?

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Induction machines don't have magnets on the rotor. Look up induction machines and induction motors and restate your question. – Jason S Jan 9 '12 at 13:48
...and for what it's worth, no electric machine that is reasonably efficient would "fight its own rotation" if it's not connected to anything. If power is being generated, of course there will be a torque exerted to slow down the rotation, since there's conservation of energy. – Jason S Jan 9 '12 at 13:52

2 Answers

up vote 10 down vote accepted

Yes, any generator will be subject to this effect.
You can't get something for nothing, so the more current drawn from the coils, the larger the (opposing) magnetic field (counter mmf) and the harder the rotor will be to turn.

If this didn't happen then the amount of energy required to turn the rotor would not change according to the load on the output, which would break the laws of physics.

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3  
You can't win, you can't break even, and you can't quit the game. – Mike DeSimone Jan 9 '12 at 15:11
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All generators work such that the output current produces a force that opposes the rotation. Think about it. This comes from basic physics without having to know anything about how a generator works. If there were no back force, there would be no power going into the generator from turning its shaft, which means no power could be coming out.

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