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(Electrical)
(OP)
18 Mar 16 03:47We're running the motor (300kW) and people have tried to get rid of vibration on it.
I've though that vibration is only about mechanical part and nothing to do with electric.
Somebody asked me if there is any elements in terms of electric that need to be considered.
Do you think there is any part we need to care as an electrical people?
please give me any advice.
(Electrical)
18 Mar 16 04:11Often the electrical part creates torque pulsation that drives vibration and resonant responses, so yes, electrical can be involved.Motors with open windings or partial failure issues can cause lots of vibration.
Keith Cress
kcress - http://www.flaminsystems.com
(Mechanical)
18 Mar 16 04:12You need to care about all the parts.
The forces within the motor that originate from current flow are much larger than the forces with a strictly mechanical origin in any motor that hasn't suffered severe mechanical damage in some way.
If possible spin the motor with some external mechanical power source, with no electricity applied to the motor itself. If that reveals no serious vibration, then...
Start by looking for unbalances among currents that should be symmetrical.
... and that's pretty much the limit of my expertise in electric motors, but maybe one of our real experts will chime in soon.
Mike Halloran
Pembroke Pines, FL, USA
(Mechanical)
18 Mar 16 19:59Yes, there are electrical malfunctions that can produce vibration in a motor. In order to help you, we need more specific information about the motor and the vibration.
What speed is it running at?
Is the motor uncoupled or driving something?
Rolling element bearings?
Has the vibration been measured? Amplitudes? Frequency content?
Answering these questions would be a start to your investigation.
(Electrical)
18 Mar 16 20:38Nice tip Mike Halloran.
Chuck
(Mechanical)
18 Mar 16 21:54There is a lot of information about motor electrical and mechanical vibration sources. A simple search will reveal a lot.
Google: motor electrical vibrations
The dominant vibration frequency from electrical dynamic force is 2x line frequency (either 100-Hertz or 120-Hertz) that is caused by magnetostriction. Some other important electrical frequencies are pole pass, rotor bar and stator slot pass frequencies.
"I've though that vibration is only about mechanical part and nothing to do with electric." Vibrations are the result of dynamic forces acting on the structure. Tip of the iceberg here!
Walt
(Electrical)
19 Mar 16 06:44Vibrations are often caused by uneven air-gap.In case of 300 kW motor always is desirable to apply a winding connection which will reduce vibrations caused by uneven air gap.
(Electrical)
19 Mar 16 06:55In addition: it is mainly related to the low-speed motors (6 or more poles).
(Electrical)
19 Mar 16 07:50I haven't figured out what kind of motor it is. VSD or Constant Speed, DC, ASIM, PM, WRIM etc?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
(Electrical)
19 Mar 16 17:33You haven't told us what the motor is driving.In many cases electrical vibration will cease the instant that the motor is disconnected.
Bill
--------------------
"Why not the best?"
Jimmy Carter
(Electrical)
19 Mar 16 17:59There are a lot of good references on this topic, like this one the electrical influences on motor vibration,This Siemens paper is an excellent resource, http://www.industry.usa.siemens.com/drives/us/en/e... When I approach a vibration issue with an electric motor driven system,I start with a discussion on the history of the problem, is it a new install? Did it start after a repair? Did it start out fine and slowly get worse or did it increase suddenly.What is the motor driving? Is the driven equipment/process changed?A walk around visual inspection, how is it mounted, coupled, shimmed? Are there signs of mechanical damage, like cracks in the sheet metal, guards or support brackets.I usually do a vibration analysis and collect electrical data with a three phase power analyzer at the same time if possible. Collect and review the data, see where the dominant frequencies are, see if the electrical data shows any possible contribution factors, and then work forward with the information collected so far to determine root cause from there. A possible corrective action may be apparent at that point, or the need to do further testing.Some problems are fairly easy to figure out, some require a large amount of effort to make proper corrective action, a lot of factors involved and not many "easy fixes", at least for the stuff I work on most of the time.MikeL
(Mechanical)
21 Mar 16 15:07Other posters have answered OPs main question about the existence of "electrically" induced vibration.
Absolutely To make any significant progress the First step is detailed vibration analysis, also as pointed out by others.
Also as mentioned by others, MUCH more info (words and pictures) about the equipment is required by whomever is working to fix the problem, if there is a problem
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(Mechanical)
29 Mar 16 21:39Hi yk,
any progress on the motor vibration?
(Mechanical)
17 Apr 16 15:40Are there any devices used in industry to isolate vibration caused by an electric motor?
(Electrical)
17 Apr 16 16:09Broken rotor bar(s) are another possibility. Somewhere I have (had) an article I clipped showing a vibration spectrum analysis profile that could be used to indicate a broken rotor bar, because it was relatively consistent and repeating. I had that as a paper copy, which may have been recycled now, but I'll take a look. If I'm not mistaken though, this has come up in here before and Gunnar (skogsgura) had shown something similar.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
(Electrical)
18 Apr 16 12:41http://www.pump-magazine.com/pump_magazine/pump_ar...Quote:
Broken rotor bar(s) are another possibility. Somewhere I have (had) an article I clipped showing a vibration spectrum analysis profile that could be used to indicate a broken rotor bar, because it was relatively consistent and repeating. I had that as a paper copy, which may have been recycled now, but I'll take a look. If I'm not mistaken though, this has come up in here before and Gunnar (skogsgura) had shown something similar.
link on degraded rotor bar detection. Vibration signature and current signature are discussed... current is a more definitive indicator (and prefer to check near full load). We've had 3 large motors with damaged rotor bar joints and evaluating a fourth right now.op has got plenty of general info to go on... the Siemens link by catserv is a good one.still no specifics from op...=====================================(2B)+(2B)' ?
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You've got a lot of good advice and I agree with everyone it sure smells like a thermal rotor problem of some type. I'll go through my thought process, sorry if I'm repeating anything from others.
Quote:
The motor is a TEFC 700HP V that had been reconditioned in '.This motor starts and stops many times per day (~20ish) both loaded and unloaded and is a cross the line startThe motor is a TEFC 700HP V that had been reconditioned in '.This motor starts and stops many times per day (~20ish) both loaded and unloaded and is a cross the line start
That's a heckuva lot of DOL starts for a large motor. Of course we all know that repeated starting over time can degrade the rotor electrical circuit (particularly the joint between the rotor bars and end rings) and that particular degradation mode will cause your symptoms and is expected to show up in current signature analysis under load. You may see an increase in slip at a given load as the rotor degrades (compare to history and sisters at same loading). You may see an increase in the time it takes the machine to come up to speed during DOL start (again compare to history and sister machines). The time it takes to come up to speed is also an indirect indicator of the inertia (higher inertia loads like fan and speed increaset tend to take longer to come up to speed and each start poses more of a challenge to the motor).
As mentioned above, problems with the rotor electrical circuit will reliably show up using current signature analysis under load, and that makes the troubleshooting easy...
Unfortunately, there are also other thermal rotor problems that are not related to the rotor electrical circuit (and would'n't show on the current signature analysis). Those include:
In the shop you can do a test where you heat the rotor in an oven to about 200F and then take it out and measure TIR and compare that to the ambient TIR profile. Positive result confirms thermal rotor problem but negative result is not decisive. I tend to think 3.B will probably show a change and 3.A may not (since 3A also depends on the temperature difference between copper and iron that is not recreated in the oven test... maybe try putting current through the rotor using clamps at/near each endring athough I've never seen that done for this purpose... current clamps are typically only used for checking the electrical circuit with thermography).
Quote:
The motor repair facility tear down reports states there are signs of heat on the rotor and stator and the no load testing indicated low vibration but nothing noted of rotor or stator issues.The motor repair facility tear down reports states there are signs of heat on the rotor and stator and the no load testing indicated low vibration but nothing noted of rotor or stator issues.
For completeness, it's helpful to fully describe the machine. Sometimes those small details trigger additional thoughts about something someone has seen unique to particular types of machines. Can you describe the bearing configuration. I assume it's horizontal. What does it drive and through what. Is it Siemens Allis by any chance? (that's the OEM whose motors have been kicking my butt with rotor problems... I'm looking carefully at 3C above ).
Also for completeness (although it seems very unlikely) is there any chance the alignment is changing with temperature. Does the vibration on driven machine increase when the vibration on the motor increases?
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