A normal AC induction motor can indeed be used as a generator but
there are caveats. First, the motor will not usually just start
generating if spun up. The field coils must usually be energized for a
short period of time. Then the magnetic field will build up on its own
if the motor, now acting as a generator, is not subjected to a load.
And if the generator is overloaded the generator will stop generating
and will not start generating again until the load is removed.
Furthermore, even though the motor must be spun at a higher RPM than
its synchronous speed, the frequency of the generated power will
depend more on external factors such as load and capacitors used for
power factor correction. All the above apply to a motor that has
windings NOT connected to the AC mains. If the field coils are
connected to the AC mains then the frequency will be whatever the
mains frequency is. Sometimes people who are using wind or water
turbines to make their own power will exite the windings of their
induction generators with mains power (for this reason as well as
others) and feed the extra power generated back into the grid. If this
is done and there is a power failure the home based generators will
cease generating electricity. Doing a google search will bring up many
links to using AC induction motors as generators. US motors has info
on their website about using their motors as generators and even
provides some examples of such use.
Thanks much for the educated responce,I new some of what you menchened,though i
am still trying two picture the difference between how a single 220 welder is
wired and how a three phase trasformer is wired and the phase wireing
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