Asynchronous Machine Efficiency

Efficiency values are basically the same in either direction.

But realize that the value on the nameplate is only the efficiency at full load, which is easier to define when motoring. It goes down (as a percentage) as the load decreases because of fixed losses in the windings and magnetics. So for a motor, full load means the mechanical power expressed at the shaft as it tries to drive the load is equal to the rating of the motor. But what is the "load" on an induction generator? You must have a sufficient overhauling mechanical load from a prime mover on the shaft to spin it at super-synchronous speed. But to get full efficiency the "load" on it as a generator would have to come from the grid it is connected to. So that actually happens only when your prime mover attempts to drive it beyond the initial super synchronous speed at which it started generating, increasing up to the point where the negative torque expressed by the grid resisting it's influence gets to the kW rating of the machine.

thanks for advance mate.....