Electrical and Mechanical Run out - Large motors

[magneticted]

Can any of you guys advise how the motor manufacturers measure the electrical run out of the bearing journals.One can understand how the mechanical run out can be checked, but electrical run out ???

 

[electricpete]

Electric runout refers to electrically-induced phenomena that affect the reading of b/n style proximity probes.

It is not an actual runout. But if you were attempting to "compensate" shaft position for runout, you would need to compensate for both mechanical runout (actual 1x-filtered shaft runout at point of measurement) and electrical runout.

http://www.bently.com/articles/apnotes/an002.asp

"Electrically-Induced Runout - In general, proximity transducers will operate satisfactorily in the presence of magnetic field, as long as the field is uniform or symmetrical and not localized to a particular location on the rotor. If a particular area or zone of the shaft surface is highly magnetic and the remaining surface is nonmagnetic or at a much lower value, an electrical runout condition will be manifest. This is due to the resultant change in sensitivity on the shaft surface to the applied field from the proximity transducers."

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[Mendit]

Measurement sounds easy but can be quite difficult to get repeatability. We do this many times on large motors in the repair shop. If you email me I will send you to the procedure we use. ipreston@kadon.ca.

If you need to correct the runout this can also be difficult to achieve. Residual gauss can be a problem any more than 3 will give poor result.

Basic, Surface finish Minimum must be ground prefered diamond burnished (5 Micro finish)

Support while testing Non metalic Vee Block (don't use the bearing) or Babbitt lined vee block.

Turning in a balance machine with hard bearing supports

Record runout with a 7200 series BN probe, capture trace on an scope.

 

[dgallagher]

We package an electrical/mechanical runout kit for measuring and documenting runout on bearing journals:

http://www.stiweb.com/downloadDataSheets/sti810.PDF

We typically provide it to turbomachinery repair facilities, larger end user's, OEM's, and service providers.

Dave G.

http://www.reliabilitydirect.com