Jerry wrote:
I like your suggestion that we dont have much real data on how fast we can
run motors before they fail and actually destroying one is probably the only
way to learn its limit.

Hmmm, I don't recommend such an experiment without the
appropriate test site. While it is likely the first thing to
fail would be a copper bar in the rotor push outward enough
to make the rotor iron hit the stator and stop the motor,
there is the possibility the entire rotor would burst
completely! I wouldn't want to be annywhere near one of these
rotors coming apart at well above 5000 RPM.

When discussing these overspeeding topics some time ago, I
believe on this same list, somebody from the UK told about a
shop that had modified motors for operation on 800 Hz in a
woodworking shop. They had 2 diesel generators, one wound for
400 Hz, one for 800. They started the whole shop on 400 Hz,
then switched to 800 Hz, then shut off the 400 Hz generator.
I don't know what number of poles they used on the motors, I'm
pretty sure they couldn't be 2-pole, 4-pole, or even 6-pole,
that is just too fast for standard rotors. Guessing an 8-pole
winding at 800 Hz, that would be 12,000 RPM, the next
possibility is 12 pole, for 8000 RPM.

(I am not recommending doing anything like this, I tend to be
REALLY conservative when overspeeding anything.)

Jon