Vibration standard for electromotor 5

[Msipad]

Dear all,
Does anyone know about vibration international standard of electromotor?

Thank you

 

[edison123]

ISO 10816

Muthu

http://www.edison.co.in

 

[electricpete]

Not international, but a point of reference:

NEMA MG-1 identifies vibration requirements for new motors: < 2 mils, 0.12 ips, 0.8 ips when tested on rigid mount. < 2.5 mils, 0.14ips, 1g when tested on resilient mount. I specify rigid mount whenever possible because resilient mount can hide soft-foot conditions and you don’t the first time you find out about that to be when the motor is installed into the plant (been there, done that, not fun).


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(2B)+(2B)' ?

 

[electricpete]

By the way the mils referenced above are pk/pk, velocity is pk/0, and acceleration is pk/0. This is different than iso which uses rms for velocity and acceleration.

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(2B)+(2B)' ?

 

[electricpete]

And by "soft foot conditions", I am talking about when the 2*LF shoots up with feet tight, disappears when loose... can't be corrrected by shimming. Happens to us on many 2-pole horizontal medium size motors. I'm done now.

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(2B)+(2B)' ?

 

[edison123]

pete

That soft foot condition (2xline frequency) can't be corrected by shimming. You meant it for resilient or rigid mounts ? In any case, why it cannot be corrected ?

Muthu

http://www.edison.co.in

 

[electricpete]

We have been through massive pain on horizontal NEMA frame motors that work fine with the feet loose but sing at 2*LF horizontal rocking mode with the feet tight on a rigid base. 2 different families of motors. Many different rigid bases attempted including: in-plant both cases, our machine shop both cases, and the motor OEM one case… in both cases motor feet were planed with no effect… in both cases the rigid bases the vibration went away with feet loose and reappeared with feet tight. Those are the symptoms of the problem. The name “soft foot” may have been a misnomer for this problem. Some people I have talked to are inclined to put a name/explanation on it: resonance, foot-related resonance, airgap distortion. I think it is a very subtle form of tuning of the coupling between the core and the stator frame. The only way the motor OEM could fix it was trimming some interior ribs between core and frame to tweak that coupling.

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[electricpete]

I forgot to mention the problem was 2-pole in both case. Actually we have foot sensitive 2*LF problem on many more of our 2-pole NEMA frame low voltage motors, but these two sets that we studied very closely.

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[electricpete]

you meant it for resilient or rigid mounts ?

The motors tested fine on resilient mount, but vibrated heavily when bolted to rigid mounts. One set were brand new motors from OEM. You can imagine buying new motors to NEMA spec which allows resilient mount.... ironically NEMA allows higher vibration for the resilient mount but our vibration was the opposite showing much higher bolted to the rigid mount (and not a resonance isolated to one particular rigid mounting... showed up in plant, in our plant shop, and at the OEM).

Sorry to get way off track. The main point was that whenever I mention the NEMA specs, I always tell people to test rigid mount. NEMA is imo silly to allow anything different for motors that are going to be installed rigid-mounted.

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[edison123]

Thanks pete. I agree 2 pole motors are generally PITA in terms of vibration.

Just last week, I had a client with 2 pole, 3600 RPM (VFD) motor with high vibration issues. We brought down the horizontal and vertical vibration from over 18 mm/sec rms at both axes to 1.5 mm/sec. All vibrations were 1X. Balancing and rectification bearing housing concentricity fixed the problem.

Muthu

http://www.edison.co.in

 

[electricpete]

The OEM tore ours apart and put back together with an eye toward concentricity - no change. I think you highlight a good point that we shouldn't discuss 2*LF vib as if it is all the same cause or same phenomenon (no-one would think all 1x is the same). Each motor is different. But testing your motors as close to their target installation as possible is your best bet.

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[Motorwinder]

http://www.dtbtest.com/PDFs/MIL-STD-167-1A.pdf

 

[Msipad]

Dear all,
Thank you

 

[Tmoose]

I like the GM / NASA one because it includes frequency ranges instead of an "overall" value.
It is harder to implement up front, but weeds out real problems better than an overall that of necessity is chubby and blind.
0.1 IPS pk of "unbalance" is less important than 0.1 IPS of bearing screech and rumble, or the 2X LF that EPete and others mentioned.