Message Board Thread - "Stator thermal patterns"

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Stator thermal patterns MH 8/4/2004
I was wondering how successful anyone has been in attempting to isolate localized heating resulting from crack rotor bars, or shorted end-rings in motors? Thermal differences degree wise that have been identified with above faults. I am trying to utilize this technology to confirm what I identify in my vibration spectral data as faults above. I would also like to hear how aluminum stator cases (covered with at least .9 emissivity media) verse sheet metal/cast steel housings show these localized hot spots.

 
Re:Stator thermal patterns Edd Hindmarsh 9/4/2004
I would be rather surprised if rotor bar faults presented localised hot spots on a stator because of the fact that the rotor is rotating. They could however cause a large increase in the stator core temperature
 
Re:Stator thermal patterns DaleH 9/9/2004
It is virtually impossible to detect rotor bar or end ring defects on induction motors while they are in service. Stator body temperature may increase, but that doesn't confirm a rotor issue. Since many rotors are manufactured such that the bars are simply not visible from the surface, a crack or break may be "buried" in the lamination. A good motor shop will have a stator core loss tester. Disassemble the motor. Support the rotor in a stand that allows rotation of the rotor. (Rolling element bearing support makes this job much easier.) Connect the tester to each end of your rotor shaft. As the rotor heats up, if there are significant cracks in the bars or separation between bar and end ring, you can usually detect them as cool spots. If the rotor bars are not visible to the naked eye, as in many cast rotors, you may need to wait several minutes for the anomalies to appear.
Hope this helps.
 


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