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Re: 3-phase current
>
> Maybe I'm missing something, and this might have already been posted, but
> can't you just use a single-phase motor to run a three-phase motor
> backwards as a generator?
>
> Steve.
Kind of off topic, but, the short answer is no, because there isn't any
rotor excitation. A standard induction motor essentially excites the rotor
by transformer action from the stator AND the difference in speed between
the rotor and synchronous speed (i.e. the "slip"). Induction motors develop
zero torque at synchronous speed for this reason.
A synchronous 3 phase motor could be run backwards as a generator, but it
would require slip rings (or some other scheme) to provide excitation
current for the rotor field. A good example of this would be an automobile
alternator, where the rotor has a single phase field, and the three phase
stator is rectified in a 3 phase full wave bridge to provide the output.
I used to have a 60-50 Hz converter that had a 60 Hz synchronous motor and
a 50 Hz synchronous generator connected with a toothed belt. (We used to
call it Satan's siren when it ran, because of the very noticeable belt
whine)...