×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Motor Vibration,high peak of 9.78 mm/s at exactly 100Hz

Motor Vibration,high peak of 9.78 mm/s at exactly 100Hz

Motor Vibration,high peak of 9.78 mm/s at exactly 100Hz

(OP)
Hi Guys,

I have a new motor we put into service 1 week ago, we took out the original to replace bearings as it had been working for 5 years (routine service). This motor has shown up the following after routine condition monitoring:high peak of 9.78 mm/s at exactly 100Hz (twice line frequency) measured at the motor drive end in the horizontal plane(pump and motor laser aligned.) Do you have any ideas as to what maybe causing this (could it be a stator problem).

Thanks  

RE: Motor Vibration,high peak of 9.78 mm/s at exactly 100Hz

One of the first things to check would be soft foot.  With proper safety precautions, carefully loosen one foot at a time and check for decrease in the twice line frequency.  Retighten and go to the next foot. A significant drop in twice line frequency indicates the problem is probably created by uneven or angled foot conditions which distort the frame. By the way, is this a 2-pole (3000rpm)?

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor Vibration,high peak of 9.78 mm/s at exactly 100Hz


Much less likely candidates – unbalanced voltage, winding problem, as-built air-gap problem.  One other easy thing to check that might indicate unbalanced voltage or winding problem would be a check of current balance.

(Again the number one suspect is foot conditions.)

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor Vibration,high peak of 9.78 mm/s at exactly 100Hz

Is this an induction motor?
If the frequency is twice motor speed, look for a mechanical or balance problem. If it is twice line frequency look for a stator problem or some problem in the magnetic circuit.
The slight difference between line frequency and motor speed is significant.
respectfully

RE: Motor Vibration,high peak of 9.78 mm/s at exactly 100Hz

(OP)
Thanks electricpete,

Yes it is a 2pl in 200 frame, the point is, it is at exactly 100hz.

RE: Motor Vibration,high peak of 9.78 mm/s at exactly 100Hz

I would then suggest a magnetic problem originating in the stator. This does not rule out electricpete's suggestion. A twisted frame may be distorting air gaps.
respectfully

RE: Motor Vibration,high peak of 9.78 mm/s at exactly 100Hz

Is it at exactly 100Hz? Or just as close as you can measure? What did you measure it with? If the vibration is caused by the rotation of the motor it will be at (line freq. - slip freq.) which will be slightly lower than 100Hz, unless this is a synchronous machine in which case slip will be zero. Exact is a risky word to use in an engineering context - almost everything outside of the world of theory has a tolerance on it.

----------------------------------
  I don't suffer from insanity. I enjoy it...

RE: Motor Vibration,high peak of 9.78 mm/s at exactly 100Hz

Pete is right on about the possible soft-condition.  Another way to check for soft-foot if you're not running is to use a dial indicator mounted on each motor foot.  Check to see if you get any vertical movement when you loosen the hold-down bolts.

RE: Motor Vibration,high peak of 9.78 mm/s at exactly 100Hz

feg

Is the motor you replaced identical in spec and manufacture as the one you removed?
Slim one this one, but worth a comment: If it is a different manf (meaning: you didn't have this problem before) then you can get a phenomena called "beat" at line frequency (50Hz) or direct multiples of this (100Hz, 150Hz), especially if the motor is of low quality (low copper content etc). It's difficult to overcome sometimes other than changing the motor make or perhaps adding an output reactor.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources