Rotating electric machines vibrations measurements
Rotating electric machines vibrations measurements
(OP)
Hi,
have anyone worked with IEC 34-14, dealing with subj.??
If so you may be able to answer me: why do it state that vibration severity should be measure at NO LOAD, when I just now realize that f.x. rotor winding interturn shorts can easily be detected as high vibrations at loaded condition!
In any case vibration measurements should of course be talken in normal operation mode, or at the load condition which give highest vibration readings - right???
Comments and experiences are highly appreciated
/Petersen
have anyone worked with IEC 34-14, dealing with subj.??
If so you may be able to answer me: why do it state that vibration severity should be measure at NO LOAD, when I just now realize that f.x. rotor winding interturn shorts can easily be detected as high vibrations at loaded condition!
In any case vibration measurements should of course be talken in normal operation mode, or at the load condition which give highest vibration readings - right???
Comments and experiences are highly appreciated
/Petersen






RE: Rotating electric machines vibrations measurements
Wouldn't the standard logically assume that your equipment is in working order? This is not the case if there are shorted windings. Then you have an electrical problem, not a mechanical one.
Wouldn't any load at all stabilize the motor and mountings, so that mechanical vibrations would be greatest at no load? How would the standard account for all dynamic conditions that might cause resonances, etc.?
Regards,
William
RE: Rotating electric machines vibrations measurements
agree with you to some extend. But what if thermal heating of the rotor, during load, for some reason causes bending of the rotor, resulting in high vibrations. Rotors are usually balanced dynamically in cold condition.
What if vibrations in load condition is severe due to above? - what is the limit for vibrations in loaded condition.
/Petersen
RE: Rotating electric machines vibrations measurements
Regards,
William
RE: Rotating electric machines vibrations measurements
Loaded and unloaded run obviously provide the best identification of possible problems.
In many cases particularly rewind of a large motor, loaded run is expensive. When we rewind a large motor we do unloaded run with vibration check. We don't get to check the loaded performance until it gets installed in the plant. For new large motor we request loaded run.
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RE: Rotating electric machines vibrations measurements
Once again I think it is a matter of convenience and cost. Purchaser can certainly request loaded test if he desires.
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RE: Rotating electric machines vibrations measurements
Weh3 is speaking the motor manufacturers point of view -
"Can the standard take into account all possible loading conditions?"
and further
"How would the standard account for all dynamic conditions that might cause resonances, etc.?"
If possible to do a full load test - should we stick to the unloaded limits? Otherwise what do you do?
/Petersen
RE: Rotating electric machines vibrations measurements
Yes, we apply the NEMA MG-1 unloaded vibration limits for both unloaded and loaded vibration data. I'm not sure if the remaining questions are directed to me but I'll give my two cents.
"Can the standard take into account all possible loading conditions?"
No. I believe no-load and full-load are good enough (excluding VFD applications).
"How would the standard account for all dynamic conditions that might cause resonances, etc.?"
NEMA gives instructions for testing either in rigid or resilient mounted configuration. Either configuration assures that mounted resonant frequency during test is well separated from running speed. However there is no easy way to assure that resonance amplification will not occur once installed. Likewise installation problems like base looseness or coupling misalignment cannot be anticipated or prevented by repair shop testing.
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Eng-tips forums: The best place on the web for engineering discussions.
RE: Rotating electric machines vibrations measurements
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Eng-tips forums: The best place on the web for engineering discussions.
RE: Rotating electric machines vibrations measurements