After a long time I am looking at my question, very good question.”Law of conservation of energy”, If you look into this Energy neither be created nor be destroyed.
Our case: Generator generates energy, this would be feed to motor, May be the rotation would happen for around 5 min, gradually decreasing speed of shaft. I am not implemented, but as per motor and generator operation some amount of energy consumes for magnetic field operation etc…
So no external energy you are feeding in , this condition doesn’t work out.