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Electric Motor Noise

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Peter Gain14/01/2011 15:23:45
103 forum posts
Does anyone have access to (or know how I can access) BS 4999-50, EN 60034-9 or IEC 60034-9? I require info re-mechanical noise from a .55kW, 3ph, 240v dual voltage motor. Do the above specs give either mandatory or guide line max noise levels? I have asked the manufacturer & the importer but they do not reply. (Why am I not surprised)?
Peter Gain.
Bill Dawes14/01/2011 17:35:34
494 forum posts
Peter i will see if i can find any info when I get back to work next week. We manufacture industrial fans so use  a lot of motors. Noise levels do vary a lot from mfr to mfr, it depends a lot on on quality of motor, (as you might suspect) ie a high efficiency ABB motor is likely to be quiter than a'cheap' low efficiency band motor although I would not expect any 0.55kw 3 phase to be especially noisy. Be aware also that catalogue motor noise is usually 'no load' we add a bout 5-6 dbA for full load.
Bill Dawes
Peter Gain14/01/2011 19:12:14
103 forum posts
Thanks Bill.
Peter Gain.
Ian S C15/01/2011 02:32:09
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7468 forum posts
230 photos
Is the motor old or new?  Or maybe Chinese. What bearings does it have, ball or plain?
   Ian S C
Peter Gain16/01/2011 20:20:48
103 forum posts
Ian SC, thanks for your interest, but I think that you have missed my point. I need to know if BS lay down a max acceptable mechanical noise for FHP motors. I purchased the motor on the understanding that it complied with the relevant BS specs. If to comply is mandatory, then I believe that I have possible claim for a too noisy product. If the BS is only a recommendation, then I will have to put the purchase down to an expensive mistake & in future steer clear of Indian made products.
Regards,
Peter Gain. 
Bill Dawes16/01/2011 21:12:55
494 forum posts
Peter, one other thing, BS4999 is replaced by EN 60034-9, I asume it has been adopted as a BS in which case it will be BS EN 60034-9. (I should add I am not an electrical engineer, just picked up a working knowledge of motors from 40 or so years as a fan engineer)
Bill D.
Steve Garnett16/01/2011 21:34:49
837 forum posts
27 photos
Posted by Peter Gain on 14/01/2011 15:23:45:
Does anyone have access to (or know how I can access) BS 4999-50, EN 60034-9 or IEC 60034-9? I require info re-mechanical noise from a .55kW, 3ph, 240v dual voltage motor. Do the above specs give either mandatory or guide line max noise levels?
 
Okay, I'll come clean - it's electroacoustics and an area that I'm rather well qualified in...
 
Unfortunately EN 60034 section 9 isn't going to help you, for the very simple reason that it only caters for motors above 1kW. The overview of what is covered is as follows:
 
This part of IEC 60034:
- specifies test methods for the determination of sound power level of rotating electrical machines; - specifies maximum A-weighted sound power levels for factory acceptance testing of rotating electrical machines in accordance with IEC 60034-1, having methods of cooling according to IEC 60034-6 and degrees of protection according to IEC 60034-5, and having the following characteristics:
- standard design, either a.c. or d.c., without additional special electrical, mechanical, or acoustical modifications intended to reduce the sound power level;
- rated output from 1 kW (or kVA) up to and including 5 500 kW (or kVA);
-speed not greater than 3 750 min-1.

Excluded are a.c. motors supplied by convertors. For these conditions see IEC 60034-17 for guidance.
The object of this standard is to determine maximum A-weighted sound power levels, LWA in decibels, dB, for airborne noise emitted by rotating electrical machines of standard design, as a function of power, speed and load, and to specify the method of measurement and the test conditions appropriate for the determination of the sound power level of the machines to provide a standardized evaluation of machine noise up to the maximum specified sound power levels. This standard does not provide correction for the existence of tonal characteristics.
Sound pressure levels at a distance for the machine may be required in some applications, such as hearing protection programs. Information is provided on such a procedure in Clause 7 based on a standardized test environment.
 
What this amounts to is that if you have a motor that you suspect falls within the remit of the standard, and it doesn't conform, the onus is going to be very much on you to prove it - and because this will involve making acoustic measurements according to the conditions laid down in the standard, it's going to cost you rather more than purchasing a new motor from a reputable source if it's a small one.
 
If the manufacturers insist that this motor conforms to the standard, then they should be able to produce at least a copy of the certificate issued by the testing house. But as I said, even if they do you couldn't use it against them because the device simply doesn't have to comply, I'm afraid.

Edited By Steve Garnett on 16/01/2011 21:36:23

Peter Gain17/01/2011 10:45:18
103 forum posts
Hi Steve,
Thanks for your very helpful posting, you have told me exactly what I needed to know.
 
I had a Tyco-Crompton single phase .55kW motor (one of the last Doncaster made units) driving my Myford Super 7. In view of the comments made on this forum last year & the claims made by the advertisers in ME, I decided to install a 3ph motor & inverter package.
 
The new motor is a Crompton-Greaves .55 kW, made in India. I wanted to leave the motor running with the machine clutch "out" between operations. How-ever, the mechanical noise is too high & I find it irritating & have to switch off. (This defeats the object of the clutch).
 
I ran the Tyco-Crompton on the bench, no load, the noise was 52dB(A) at 1 metre. The Crompton-Greaves, no load, primary belt removed, noise was 67dB(A) at 1 metre.
 
Some data provided by "quality" motor manufacturers obtained from the internet, typically gives figures for FHP motors of .55kW as from 47 - 52 dB(A) at 1 metre.
 
In view of your comments I will have to write this of as an expensive mistake. At least I now know that it will be fruitless to pursue the matter with the supplier. Your last paragraph is particularly helpful.
 
Regards, Peter Gain.
Bill Dawes17/01/2011 12:40:12
494 forum posts
Peter, not back at work yet, I 'only' work 3 days, (despite 'retiring' 4 years ago) Guess my findings would be as Steve's. 67dbA does seem high for such a small 3 phase motor.
I know Brook & Crompton motors are made in India, I think they are old designs but were of course originally from quality mfrs. Copying a design does not of course ensure original quality in electrics or mechanical.
 
I am sorry to say we do use a lot of chinese made motor as does a lot of UK industry these days, pressure of competition has forced this. I have to say however that we have very few problems, the truth is that there are some very substantial  chinese mfrs these days with state of the art factories. The encouraging news is as their labour rates  and cost of shipping rise, far eastern stuff does not have the advantage it once did.
 
There are signs that manufacting is returning back to Europe, we are certainly very busy.
 
Sorry to digress from your original question, thought it might show all is not yet lost for UK mfg, a subject I assume to be of interest to all ME's.
Best regards
Bill Dawes
Keith Long17/01/2011 13:02:05
868 forum posts
11 photos

Peter

If the motor is making excessive noise running light then you may still have some scope for dealing with it. Firstly, if you haven't already, speak to the suppliers about the problem as the motor may well have a fault in the bearings or somewhere else giving rise to the noise. Does the motor sound noisy running on the bench and not in the lathe - you might be getting a resonance in the machine that is amplifying the noise - don't assume that 'cos you didn't with the old motor that you won't with the new - it's a different motor and will have a different residual out of balance for example. Have you got the motor bolted down hard or on resilient mounts - it's surprising what a difference those can make.

Other things to look at could include any balancing arrangement that is on the clutch components where they fit to the motor - are they still present AND correct for the new motor?

Keith


Peter Gain17/01/2011 16:19:43
103 forum posts
Hi Keith,
Thanks for your observations which are very valid. 
 
I omitted to say that I have had 2 Indian motors. The first one was noisy, I did not measure the output but simply compared it "by ear" to the UK made single phase motor. The seller willingly supplied another motor.
 
This second one was run on the bench & then the UK Tyco Crompton was run in the same position. The readings were obtained using a buget price meter that I was assured would give meaningful results, but however, would not be considered good enough for (say) a court hearing. The figures were as my previous posting
 
The first motor is still on the lathe & delivers the same 67dB(A) at 1 metre as the did the second one. Virtually no difference is noted between "on the bench" & "on the machine" values. I was informed by the supplier that resilient mounts were not necessary for 3ph motors.
 
I measured the sound levels with the lathe primary belt removed to eliminate noise generated by the belt & countershaft. I also measured with the belt & countershaft in motion. Very little difference was noted.
 
I have not named the supplier as he has been helpful to the extent of sending another motor at his expense & I consider that he has made a genuine effort to address the problem.
 
It could possibly be that both motors have come from the same rogue batch. However, my previous experience of Indian made products is that they have not yet managed to get the words "quality" & "control" into the same sentence! 
 
By comparison, my previous lathe was a factory re-con ML7, without a clutch. The single phase UK made Crompton motor, countershaft, & mandrel when running were unobtrusive. I now have an excellent lathe operated by a noisy buget motor. We live & learn!
 
Peter Gain.
 
Keith Long17/01/2011 17:31:26
868 forum posts
11 photos

Hi Peter

Looks like you've tried most of the possibilities. If they are from the same batch then I think they're doing pretty well with the "quality control" - pity they can't control the quality to a higher standard!

Seriously there isn't that much in a motor to generate noise. Can you get an idea from the "pitch" of the noise as to whether it's bearing related or from the windings/laminations. The first I'd expect to be a lowish pitch "rumble", the second  a higher pitch whistle/whine. If the latter is it there with a mains 3ph supply or only with the inverter supply? The other possible source that springs to mind is the cooling fan and housing.

If it does turn out to be bearings, then it may be damage resulting in the journey from India. Ball races don't like being subjected to vibration while they are not running. You can get track damage from the minute "hammering" effect that then shows up as roughness in running and noise. The solution to that is the obvious - change the bearings.

If you can't get a quiet motor from your supplier - who sounds as if he's being very reasonable it might be worth investing a bit of money in some new bearings to see if that makes a useful difference - assuming they are ball races, Plain bushes might be more of a problem - but would probably run quieter as well.

Keith

Billy Mills17/01/2011 18:26:45
377 forum posts
Peter,
Would suggest the large wooden stick to the ear method. With the far end pressed firmly against the bearing covers you can listen to the noise from the bearings at each end. Be careful that the stick does not slip, don't use a screwdriver!
 
Apart from the bearings the other sources of noise are likely to be poorly clamped laminations or poorly varnished windings both of which will buzz at a multiple of 50Hz. A special air drying varnish is used to secure windings and laminations which does not damage the enamel insulation on the windings.
 
A slightly more scientific method would be to use a spectrum analyser. Fortunatly there are some very good freeware downloads that run a fast Fourier transform on a PC soundcard to give a realtime spectral display. Spectran from www.weaksignals.com is an easy program to use with a modern electret mic in the mic input.
 
Bearing noise will be broadbandish, winding or lamination noise a multiple of 50Hz, a periodic rotational noise will be slightly lower in frequency than the mains because of "slip". Bet you can't resist making silly noises and looking at the spectra!
 
Regards,
Alan
PekkaNF17/01/2011 19:01:20
96 forum posts
12 photos
Pretty sure buyer on the mfg side has bought the bearings on price only. Electric motor bearings used to be of tighter tolerance than for agricultural use. Many easter mfgs will print on the box whatever and lot of buyers would buy on first few digits right on the bearing code anyway. It's really amazing difference what bearing does.
 
Seriously. I heard one sick motor and everything else was correct (even the bearing type) and OEM manufacturer had it right. However  the manufacturer of the gear unit had failed on pre paint wash = most of bearing grease was lost and replaced with solvent and detergent! After shipping it over the pond and keeping it in  the ware house for a year, had bearings heading south in no time.....
 
I'm pretty sure you tested it without load. Have it coast down and there you have bearing sounds only....laminations make sound only when powered up. If the sound comes from lamination....ditch it.
 
PekkaNF
Billy Mills17/01/2011 20:17:57
377 forum posts
Think that the conclusion should be after the test and examination. If the windings or laminations are the source then 20p's worth of  the right varnish in the right place should fix it without complications. The bearings are best tested on load but if they are rattling around new then the remedy is obvious. Either way around you have to take the motor apart and be carefull...
 
Regards,
Alan.
Steve Garnett17/01/2011 22:25:50
837 forum posts
27 photos
Okay, one or two points, mainly as background information: the measurement standard actually specifies two ways of measuring the motor noise, and only one of them can be carried out with an SPL meter. But even if you have one, you'll also have to have a standard measurement microphone, and a means of locally calibrating it before any measurements you made at all would be entertained by anybody else.
 
The second method of measurement is in fact the more useful one, because it expresses the overall noise as a power measurement. To do this though, you need to measure the sound intensity in a defined area, and that you simply cannot do without the right, very expensive, equipment. If I do this, I have to hire or borrow the kit - it costs thousands of pounds to purchase. Having done this all around your motor, and got the machine to compute the results, you end up with an answer to how much acoustic power the motor radiates, in W/m^2. But having done this, you can also map the results, which is where the intensity measurement comes into its own. This way you can actually tell where the majority of the noise is coming from, because this is in essence a vector measurement.
 
As for the actual amount of noise, which you've said is around 15dB higher on the new motor, well yes - that does seem to be rather high. Since I don't see how the laminations, however bad they might be, could produce this much broadband noise (which is what you will have been measuring) and still have the motor working properly, this has almost certainly got to be bearing-related. So since you are stuck with the thing, then Keith's comments seem particularly relevant!
Nicholas Farr18/01/2011 00:34:57
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3059 forum posts
1389 photos
Hi Peter,
               it sounds as if it could be bearings. Bearings made by reputable manufacturers are almost certainly better quality. Keith is correct when he says bearings can suffer damage when they are not turning, even when they are in storage and still wrapped, allbeit a slowish process, but if a motor is stored for long periods in an enviroment with vibration. this can speed things up a bit with the weight of the rotor on them.
 
Examaning the bearings is probaly worthwhile, and changing them isn't such a big deal, just don't knock the rotor or the windings about.
 
Regards Nick.
Billy Mills18/01/2011 02:08:14
377 forum posts
I would readily agree that the bearings are the most likely problem but it is surely better to listen to the bearings- at both ends- with a stick of wood to hear the sound of the fault. If the bearings are noisy( and maybe the shaft will move axialy) then the noise is a grinding sound- but nearly all ball  bearings will make some noise of this kind. If there is a buzz involved then loose lams or windings may be involved.
 
I have seen cages rocking on shafts and 1 case of a rotor rotating at normal speed with a completly stationary shaft on a very expensive swiss machine so I do not rule out anything without hearing what the symptoms are before dis-assembly.
Other encounters have been untied/unvarnished windings and foreign ferrous objects - like the e clip that the service person dropped or the tiny rare earth magnet that dropped out of a reed  door switch that ended up inside the ali cased motor on the lam stack and made an extreeeemly loud noise. Always the first clue is the nature of the sound but I now never try to underestimate human activity- it delays finding the solution.
 
Steve's sperical integration is not so great, you need a chamber, the gear and a lot of time to integrate  positions, hardly at home stuff. I will stick with my wooden stick and personal aural analyzers or Spectran if I want pretty pictures.
 
regards,
Alan.
Nicholas Farr18/01/2011 03:24:42
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3059 forum posts
1389 photos
Hi Alan,
              I agree that listening in the first place is the approach to the problem, prferably with a dedicated stethoscope, but your stick will give you a good idea. In my previous post I assumed all other avenues had been pursued.
 
A rotor rotating on the shaft!! very unusual, as they are normaly a press on fit. I've known a cracked bar in the cage, which often points to problems that don't stack up. Higher than normal amps with no logical explination is one clue.
 
Regards Nick.
Steve Garnett18/01/2011 07:55:20
837 forum posts
27 photos
Posted by Alan Gray 1 on 18/01/2011 02:08:14:
Steve's sperical integration is not so great, you need a chamber, the gear and a lot of time to integrate  positions, hardly at home stuff.
 
That's sort-of true - although in practice once you have it set up, it doesn't take so long to do as to be impractical. And it's also the way that most reputable manufacturers have products type-tested, simply because you get a better real-world result from it, and it's not distance-dependent. But because the measurements are vector-based it's more important to have a quiet background all around what's being measured than to worry about using a chamber (unless of course this is the only quiet background you have available!). And believe me, you can do it at home... but it's still expensive, and you'd plan to do a batch of measurements all together to amortise the costs, ideally.
 
Once you have an LwA value, it;s relatively easy to convert it to an SPL at a given distance, but you can't do this the other way around.

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