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Bearing Noise in 2400 KW, 6.6 KV HT Motor

02/06/2017 6:26 AM

Dear sir,We are having a 6.6 KV, 2400 KW,992 RPM,HT amps 267 HT motor for our Vertical Raw mill. It is running at 2200 KW load.The details of motor bearings are i) on DE side:NU244C3 and ii)On NDE side:NU244C3 + 6244C3.Frequently we are observing hissing sound from the NDE bearing and when we lubricate the bearing, the noise is subsiding.But,in a span of 3,4 days ,again ,noise is coming.This phenomenon is occurring frequently.But,we are not finding any abnormality in vibration levels and temperature is also normal.Please explain me the reason for this behavior and suggest me the action plan. The motor is CGL make and commissioned in 2009 hardly run for approximately 20000 Hours.Thanks.

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#1

Re: Bearing Noise in 2400 KW,6.6 KV HT Motor

02/06/2017 10:22 AM

Sounds like your bearing is wearing out. (Pun intended.) Particularly since lubricating the bearing removes the noise.

You include a contradiction in your description. If you hear a noise then a vibration is happening somewhere. The amplitude of that vibration may be too small for your other sensors. You may even find an under-damped incidental resonator (sheet metal) may be making this tiny vibration audible.

I would consider taking a temperature measurement of the bearing in operation before and after lubrication. If the bearing runs cooler after lubrication then it is slowly tearing itself apart. Unfortunately an identical temperature will not preclude excessive bearing wear. However, a temperature rise with no lubrication might prompt management enough for repairs to be performed before other parts get damaged, too.

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#6
In reply to #1

Re: Bearing Noise in 2400 KW,6.6 KV HT Motor

02/07/2017 4:47 AM

We have taken the temperatures of the bearing before and after lubrication.We found that temperature is raising after lubrication.

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#10
In reply to #6

Re: Bearing Noise in 2400 KW,6.6 KV HT Motor

02/07/2017 10:52 AM

OK. You now have proof that this bearing is starting to fail. If you are lucky then this bearing has just developed too much play and will not completely fail soon. Since your grease is liquefying, I don't think you are lucky. I suspect parts of this bearing have seized as JRaef's link explains in the over-greasing explanation. (Nice link JRaef. )

Take your data to management and recommend they schedule a bearing replacement before a complete failure damages more parts. Be prepared to estimate downtime, repair costs and complete failure costs.

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#12
In reply to #10

Re: Bearing Noise in 2400 KW,6.6 KV HT Motor

02/08/2017 11:17 AM

Some good points have been made. We do not have enough information, although this part about temperature increase just after lubrication addition is somewhat disconcerting. That sounds like a bad bearing to me. Can you hear it from where you are also?

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#2

Re: Bearing Noise in 2400 KW,6.6 KV HT Motor

02/06/2017 11:22 AM

Is the motor being run from a VFD? If so, that's a frequent contributor to premature bearing failure if not properly addressed. If not, another surprisingly common cause is OVER greasing the bearings. There is such as thing as too much.

http://www.belray.com/bearing-failure-due-over-lubrication

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#7
In reply to #2

Re: Bearing Noise in 2400 KW,6.6 KV HT Motor

02/07/2017 4:50 AM

The motor is not for VFD.We are lubricating the bearing as and when the hissing sound is heard.And also,we are observing that grease is getting into liquid form.But temperatures are normal.

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#11
In reply to #7

Re: Bearing Noise in 2400 KW,6.6 KV HT Motor

02/08/2017 11:12 AM

Are you certain about the quality of this grease? Is it breaking down under your conditions?

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#3

Re: Bearing Noise in 2400 KW,6.6 KV HT Motor

02/06/2017 2:05 PM

Having worked on a 3000HP raw mill I’m surprised to could hear anything, never mind track it down to one bearing.

As others have said, over greasing is a killer for bearings.

I will add this, has the drive been checked for alignment? Mill bearings are more robust than most motor bearings.

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#8
In reply to #3

Re: Bearing Noise in 2400 KW,6.6 KV HT Motor

02/07/2017 4:52 AM

Alignment is checked around 3 months back.We found it alright.

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#4

Re: Bearing Noise in 2400 KW,6.6 KV HT Motor

02/06/2017 3:49 PM

This Vertical Raw Mill? What is it milling? Is this a high dust environment? Are you intermittently getting some form of grindable particle into the bearings, and lube is washing this out (restoring normal sound of operation)?

These and many other questions, maybe you should ask yourself. and answer them to yourself.

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#9
In reply to #4

Re: Bearing Noise in 2400 KW,6.6 KV HT Motor

02/07/2017 4:56 AM

This vrm is used for lime stone milling in a cement plant.Though fine dust is around the environment,it is not very dusty environment.

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#5

Re: Bearing Noise in 2400 KW,6.6 KV HT Motor

02/07/2017 3:29 AM

What did the motor manufacturer say after its technical specialist came in to see and hear the motor, please?

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