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What I don't understand about induction generators (among other things) is: is the speed of the generator going to be limited by the grid frequency that excites the armature, or will it turn close to its optimal speed?

I have an nano-turbine that operates on 3.3 lbs/hr of steam. It's ideal rotational velocity for peak efficiency is about 80,000 rpm (fyi: it uses magnetic bearings). I want to put an induction generator on it to produce grid connect AC. What I don't understand about induction generators (among other things) is: is the speed of the generator going to be limited by the grid frequency that excites the armature, or will it turn close to its optimal speed?

Xerus, I don't believe you can use your nano-turbine to drive an induction generator or motor at the speed stated. But, a homopolar-generator might work.

Try contacting The University of Texas, Balcones Center for Electromagnetic Research, in Austin, Tx. In the '80s they had 15-20 k-rpm machines. And, I recently heard about 50-60 k-rpm units.

However, be aware that there are several drawbacks. Such machines generate only dc, meaning: they have slip-rings and brushes; they operate for short-duration; and they're massive!

But, you can never tell where a contact will lead... they might be able to point you in the right direction!

Good luck! Phil Corso (cepsicon@aol.com)

Thanks for the lead. Also, why is it that you don't think an induction generator will work?

With a homopolar-generator, keeping the brushes in contact with the slip rings and avoiding excessive friction would require some very careful engineering. Of course, doing *anything* at these speeds requires careful engineering. The output is also low voltage and high current, which might not match too well to a standard inverter.

A permanent magnet generator might be a better solution, if a suitable design can be found. The output (which would be higher voltage than a homopolar generator) could be rectified and then put through an inverter. If it is possible to have a coreless design for the stator (I haven't seen one though) this might address the problem with iron losses at high frequency.

The above is speculation, and I can't recommend any particular sources of information.