On Saturday, November 16, 2013 8:04:47 PM UTC-8, Jon Elson wrote:

So, what is a difference between a 3 phase generator and a 3 phase motor?

Absolutely no difference between an induction motor and an induction
alternator, except the cap bank for excitation.

There's a VERY BIG difference in a standard AC motor (squirrel-cage
hysteresis type) and a generator or alternator. The rotating core
of the motor is not connected with any kind of wiring to create a field
in that core, and the residual magnetism of that core is very low.

A large truly synchronous induction motor, however, DOES have slip rings,
or a commutator, and can be made to generate electricity. So can
a small synchronous motor (permanent magnet type).

All electrical machine are supposed to be reversible.

Yes, and no; the problem here is that the core is magnetizable with
continuous application of external field (powered by the AC that drives
the stator), but becomes demagnetized easily (and if the rotor isn't
magnetized, it's symmetric: it has no poles, so no generation of electricity).