On Dec 2, 8:37 pm, Telamon
wrote:
In article ,



David wrote:
Telamon wrote:

You post about the strangest stuff. I have never heard of this kind of
problem. One or more of the rotor windings must be some how shorted to
the shaft.

Ceramic bearings are not the solution as the current can go through
whatever gear train and mechanical load to which it is connected. The
motor shaft should not be electrically hot. That would be a shock
hazard. That motor is either built wrong or designed wrong.

It's a conductor in a changing magnetic field. A difference of
potential is created.

It's a conductor that is supposed to be in a net neutral magnetic field
so no potential is created.

--
Telamon
Ventura, California

In the real world, there is not a net neutral field at the motor
shaft. In smaller motors, with sinusoidal wave forms, the amount of
current is tiny and many bearings can handle it pretty well.

This has been a well known problem with large motor and generator sets
for many years. Typically, these units have three bearing pedestals,
one at the motor end, one at the generator end, and one in between.
The bearings are sleeve type bearings, and all but one pedestal is
isolated from ground to prevent the destructive circulating currents.

With the advent of variable speed drives, this type of problem is now
being seen more in smaller motors, due to the "interesting" resulting
waveforms.

Bob