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Anonymous Poster #1

High Vibration on 11 kV Motor

03/20/2014 5:05 AM

We have high vibration after greasing job on 11kV ABB motor . On the name plate in motor body mentioned "Re grease every running 4000hours until clean grease emerges" bearing type is 6330 C3. When 4000 hours running reach we used to perform greasing job until clean grease emerges.Same way of greasing up to 8000 hours greasing was no problem, But when greasing job performed on 12000 vibration become high on NDE bearing.In vibration Report mentioned

Motor vibration is very sensitive to ambient condition .If ambient temperature increasing then motor radial vibration also increase.

When we apply air hose for cooling of the bearing the vibration also decrease.

We have doubt with the greasing quantity which mentioned until clean grease emerges. Please give idea or suggestion about this vibration problem.

thanks a lot for the help

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#1

Re: High vibration on 11 kV motor

03/20/2014 6:14 AM

Have I got this right, your forcing new grease in to force the old out?
Over greasing and bearing damage springs to mind.

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Anonymous Poster #1
#2
In reply to #1

Re: High vibration on 11 kV motor

03/20/2014 7:25 AM

Yes we forced old grease out, We are worry it is over grease. Machine has to run up to next 5 years shutdown for our compressor... but after we apply cooling with air hose vibration reduce i hope it will be OK

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#3
In reply to #2

Re: High vibration on 11 kV motor

03/20/2014 1:04 PM

Hi,

Try to obtain "Air Movers" to maximise the cooling flow over the motor while minimising the air consumption.

I hope you find the problem soon.

Best regards,

John

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#7
In reply to #2

Re: High vibration on 11 kV motor

03/20/2014 11:33 PM

Well it may very well fail well before then regardless of what external attempts you try and employ to solve the bearing over-grease/polluted grease problem.

My advice is shut down, de-grease and re-grease properly (with the correct grease) following manufacturers instructions and best practices otherwise you will probably be in for a costly repair and unplanned shutdown!

Don't compound the first mistake by waiting and hoping it will all be fine, better to stop and fix the actual problem now.

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#11
In reply to #2

Re: High vibration on 11 kV motor

03/21/2014 6:22 AM

An old trick is remove the grease point and allow to bearing to force out the excess. Usually works.

As for trying to keep the motor going by cooling the bearing, it will end in disaster.

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#12
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Re: High vibration on 11 kV motor

03/21/2014 7:29 AM

The Greater risk is that most of excess grease after melting due to overheating Oils contents of the grease thins down - leaks out of clearance between shaft and inner end cap - gets sucked in by motor fan and spreads over winding. Bad effects are:

1. The lubrication quality of grease is reduced (Grease is Soap + Oil, soap is to retain grease thick enough and store oil in it for lubrication.) As a result of overheating, a thin grease consisting of RELATIVELY more oil and lesser quantity of soap leaks out of gap between Bearing cap and shaft. Remaining grease in bearing is relatively lower in oil contents.

2. Oil softens the insulation.

3. further if this is IP23 motor, grease spray on winding will collected dust and also effected cooling of winding.

So over greasing is never the right thing, Motor should be stopped and

1. Remove excess grease from outer caps. Empty to half. (To remove grease from inner cap, the motor has to be dismantled. May not be feasible - being Base Load Power Plant). If Poster does not have trained mechanics hire one as if the shaft is rotated once outer caps are removed, position of inner caps may change and will not be able to fit the outer cap. PRECAUTION: As soon as we open all screws of outer cap and slide it outward (away from housing), we immediately fix at least one screw back so that if accidentally shaft turns the inner cap stays in position with bearing housing.

2. If IP23, clean excess grease sprayed on overhang with dry clean cotton cloth followed by slightly soaked in a solvent (select solvent which will evaporate at ambient temperature and is not Chlorine based).

If it is IP54 clean on first available shutdown.

I am also based in India, if necessary poster can use my services or I can recommend service house which does similar work and have enough manpower and truck with necessary tools and tackles to do the job.

Good luck.

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#13
In reply to #1

Re: High vibration on 11 kV motor

03/21/2014 12:50 PM

I agree that over greasing can be a serious problem. If the mfg instruction is "Re grease every running 4000hours until clean grease emerges", I would call them for direction. If any question, I would replace the bearing before something bad happens. -- JHF

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#4

Re: High Vibration on 11 kV Motor

03/20/2014 1:47 PM

What did ABB say in response to the call that was made on this topic to their Technical Helpline?

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#5

Re: High Vibration on 11 kV Motor

03/20/2014 10:28 PM

Hello Anonymous,

What colour is the grease that you remove? If it is dark or black this is a symptom of overgrease but also a symtom of other things like undergreasing!!! Since you have done this activity a few times, Like the previous comment i would ask ABB for a motor perspective but also SKF. They normally very willing to help.

Does the bearing temp monitor as well (how hot?)

SKF will want that kind of info to help with your issue

Noob

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#6

Re: High Vibration on 11 kV Motor

03/20/2014 10:36 PM

A thunk test would be useful. However, I think you have overgreased your bearings. You have probably unseated parts of the bearing.

Perhaps these guys can help.

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#8

Re: High Vibration on 11 kV Motor

03/21/2014 12:39 AM

Rise in temperature is due to over greasing.

1/4 of space in end plates is kept empty for expansion of grease when hot.

Vibrations are also resulting from over heating- possible that the minimum required clearance between balls and race is not sufficient to sustain layer of lubrication. Normally it starts with screeching noise. To avoid these almost all motors and generators have Anti-friction Bearings with C3 clearance (when manufacturing based on machine tolerance and measurements bearings are labelled C1, C2, C3. C3 being maximum +deviation in clearance between inner bore of outer race and outside dia of inner race).

Rules of greasing of bearings during Preventive Maintenance Interval are:

1. Always grease when motor is running at rated speed. So that displaced old grease comes out.

2. Do not over grease. General instructions on Name plate are to grease "X" grams of grease of type "Y" every "Z" running hours.

3. Best way is to ensure 2 above is to fill up grease gun with grease, give one full stroke to grease gun and weigh the grease pumped out.

4. Next couple gun to greasing plug and just give number of strokes to meet quantity "X". Every stroke wait for few seconds watching bearing temperature. It shall not exceed 5 to 7 Deg C during the process. And after few hours of running the temperature will come down to normal running operation.

Replacement of total grease is desirable not earlier than three years of continuous running of motor/generator. And replacement of Bearing shall not be earlier than 3 years of running (18 to 20, 000 hours of running for H40 design of bearing - which is minimum for continuous duty machines).

Total packing of grease in bearing is also done if motor is going to be stored without operation of long duration - as protection against corrosion, which has to be taken out before taking in service.

During Preventive maintenance every which is 4000 hours in this case, we just replenish spent grease the quantity is approx. 1/3 of capacity of greasing cups (end plates). If quantity is not specified (I am surprised that ABB has not done that), weigh approximately 1/3 of bearing caps capacity and pump only that amount of grease, but slowly observing rise of bearing temperature.

And in case your motor is Class F then use Shell Salvania G3 or equivalent from Esso and other reputed brands which have lithium based formulation for the required duty. If it old Class B motor then continue with grease type being used.

My experience with grease type is few years older and would request other members to update with their experience as there may be new greasing products in the market.

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#9
In reply to #8

Re: High Vibration on 11 kV Motor

03/21/2014 1:21 AM

From past experience with HV large power output especially if a 2 pole machine then many manufactures will say at x hours REMOVE Plug on bottom of grease plates and restart the machine and relube the bearing till fresh grease appears from the plug hole.

AND then the instructions should read leave plug out till no excess grease is noted after machine has run for x minutes or hours.

If one stops machine then removes plug and relubes in the shut down mode then old grease will not be completely expelled.

So on restarting with plug in excess churning takes place with contaminated grease old and new and bearin will overheat.

Are you positive the new lubricant is right type, was new, properly mixed and utmost care was taken with cleanliness of associated equipment and personnel observed strict contamination standards.

If you drop the plug out one assumes this can be done safely with machine running releasing grease migh help.

If sticky oil only comes out and sample has any gritty feel schedule a bearing replacement extremely urgently.

Check out Electrical Appartus Service Associatio, FAG Bearings. SKF Bearings on WEB and learn about regreasing Electric Motor bearings.

Relubrication of any electric motor especialy large HV high speed machines requires specialist knowledge, equipment, procedures and training.

Ask any major electric motor repairer what are the primary causes of electric machine failure.

Excessive, lack of, or wrong lubrication being applied to bearings.

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#15
In reply to #9

Re: High Vibration on 11 kV Motor

04/03/2014 12:26 AM

I would like to pose a question for all.Is regreasing for motor to be done while it's running or it's in off condition?.In one of the topics written an expert says that,if done during running, the chances of grease entering inside the motor winding is more.

Is anybody aware of any best maintenance practices?

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#16
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Re: High Vibration on 11 kV Motor

04/03/2014 1:01 AM

In the off position, and preferably in the off-the-shaft position. It would be nearly impossible to grease a bearing that is running. And doing so would be, In My Humble Opinion, impossible. (I don't use the word impossible much any more....somebody somewhere has figured out how to do the impossible every day!) But greasing bearings seems to be a dark art to a lot of people. Its not hard to do. Take the bearing off every year or so, clean all the grease out of it, let it dry thoroughly, then regrease it properly. It will last for decades! Don't ever over grease...it just leads to problems. If you don't know what over greasing is, then find out. Its a leading cause of failure and must be avoided. Most over greasing occurs by an extra crank of the grease gun to make sure the old grease is forced out and the new grease replaces it. First of all, it won't replace it, even if it is running, and secondly, you have failed to clean the bearing. Any contaminants will still be in there. Occasionally you will find bearings which have a plug which you remove to allow grease to be installed without removing the bearings. This may seem to be a great time saver. However, the bearings have to be run for a half hour before you have to turn off the motor, and replace the relief plug or plugs. So I don't see how you save any time by skipping what I regard as best maintenance practices in favor of "okay" maintenance practices.

The science of bearing lubrication is changing every week. Mostly due to new "miracle" greases. But some things are universal. This is one of them.

bottom line... No, don't do it when it is running. Read this thoroughly. Especially the part where they describe the catastrophic failure caused by greasing bearings while running. Then come back with more questions....

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#10

Re: High Vibration on 11 kV Motor

03/21/2014 1:38 AM

CR4 Admin: Spam: This post was modified because it contained advertising outside the Commercial Space forum. Please review Section 14 of the CR4 Site FAQ about advertising.

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Re: High Vibration on 11 kV Motor

03/21/2014 5:12 PM

Reported as spam. See other post by same member.

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