Engine driven EDF

Question

We all know that an electric motor can be reversed to generate electricity. My question is, will it work the same way if I were to do this in an EDF?

The EDF that I’ve been watching, is producing 35 kW at around 18k RPM, that’s all I care about. Now, let’s say this EDF is driven by an engine, will it still produce approx. 35kW at around 18k RPM?

Second question, if an electric motor is rated at 15kW, 8,000 RPM. What if this motor is driven by an engine at 12,000 RPM. Will I be able to produce more than 15kW? Assuming, we have a proper cooling system.

Answer 1

You should be able to. If it has a permanent magnet rotor, it would produce current just by spinning it. But I don't think you would get the same amount of power out at the same speed simply because of the inefficiencies. A motor will always take more electric power than its actual output, and will always produce less electric power than what it takes in the form of mechanical energy.
In short, I don't think you will get 35kW at 18,000RPM.

To your second question, the answer is yes, the motor (or a generator) will produce more power at higher RPMs, but this will mean both higher voltage and current than what its windings (wire and insulation) and contacts were rated for.
Overheating will not be the only problem, but also the stress on the insulation AND the mechanical stress on the whole structure because of significantly higher forces at higher speed. Additionally, hotter wires and frame would have reduced mechanical strength, and things might start falling/flying apart.

Answer 2

Assuming an AC motor, at 35kW the motor is not likely spinning at 8,000RPM unless it is being driven at the higher speed by what's called a "Variable Frequency Drive" (VFD). If it is, then most VFDs in that size range are not "4 quadrant", meaning they will not allow power to flow the other way.

An AC induction motor CAN become an AC induction generator if the motor is made to spin FASTER than the grid power that it is connected to. But if not connected to grid power (to excite the windings), an AC induction motor cannot be used as a generator. You would need either a "Synchronous Motor" that has separately excited rotor fields via slip rings (highly unlikely at 35kW) or you would need motors with Permanent Magnets, which are VERY expensive in that size, so also unlikely.

If these are DC motors, they could be permanent magnet DC, in which case they would work, but again, not likely at 35kW on a fan.

Bottom line, probably not workable with the information you have provided.