On 2010-02-18, Joseph Gwinn wrote:
In article ,
Bob Engelhardt wrote:

I have a 1 HP 3 ph motor that I don't want & nobody else does either. I
also have a VFD that will go to 400 Hz. The recent discussion about the
rpm limits of motors prompts me to see what happens.

So I'm gonna' hook up the motor, crank the VFD to 400 Hz & stand back!
But I thought that I'd give you guys a chance to make predictions. What
do you think will happen?

Bob

Oh - the motor is 1755 rpm @ 60 Hz = 10500 @ 400. It is older & dirty
inside. The bearings? I dunno - it spins pretty easily.

Well, it could well burst at six times design rpm. I would put sandbags
around it, just in case, because the stored energy will be quite large
at near synchronous speed. Energy varies as the square of speed.

What may also happen is that eddy current losses at 400 Hz are very
large in a motor designed for 60 Hz, so it melts instead.

I would highly recommend to tape a video for such a test. I have not
had a motor ****ty enough to not feel sorry about destroying it, but I
personally would love to see the video if Bob does it.

Bob, if you do this, give the motor some time. I do think that it
should self destruct from one cause or another. I think that bearings
should melt if the motor does not disintegrate before.

Higher speed means more pressure on bearings from centripetal force,
and at higher linear speed, so the heat generation in bearings should
be speed squared, I think. This means that at 6.5 times design speed,
the bearings will generate 44 times more heat.

i