Motor Whining
Motor Whining
(OP)
I am trying to learn what I can about Motor Whining. We have a cooling tower motor at our building that has a significant Whine. It is served by a VFD and I'm thinking that this may be the reason. Anyone have any input in this regard?






RE: Motor Whining
Not all VFDs are capable of this, especially as you get into larger horsepower (you didn't say what it was), but it is worth checking out if the noise really bothers you. If not, leave it alone. It is not hurting the motor, in fact lower carrier frequencies are better for the motor than higher ones.
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Motor Whining
It sometimes, not always, results in a more acceptable sound from the motor. Sometimes it also gets more annoying - sounds like the bearings are full of sand or very near their end of life. If the option is there, just try it. It doesn't cost anything and it doesn't hurt motor or inverter.
Sometimes, you can even go down in frequency to avoid resonances that you may have in motor, fan or supporting structure. If, for instance, your carrier frequency is 2.5 kHz, it may be a good idea to try something like 2 or even 1.6 kHz.
There is also (the rather expensive) solution to add a sine filter between VFD and motor. That will give you the best solution. Quiet motor and reduced bearing problems.
Gunnar Englund
www.gke.org
RE: Motor Whining
Or just spread it over a broader spectrum to defeat the EMI tests...?
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Sometimes I only open my mouth to swap feet...
RE: Motor Whining
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Motor Whining
"skogsgurra, ..It sometimes, not always, results in a more acceptable sound from the motor. Sometimes it also gets more annoying - sounds like the bearings are full of sand or very near their end of life. "
skogsgurra, It's true. Such audible emission really annoying!
We have a problematic machine. To the extent a thorough check up of the unit was resorted, ended up to found nothing except the VFD itself is the culprit until tuning up was carried out.
RE: Motor Whining
Gunnar Englund
www.gke.org
RE: Motor Whining
increasing the carrier frequency on certain drives and certain makes will automatically de-rate the drive (reduce the output current capability), so increasing the carrier frequency, whilst it will reduce the audible noise, may create other problems with the drive system (e.g. the VFD going into current limit). So be careful and take any steps gradually (i.e. if your CF is 2kHz, don't go straight to 16kHz) and observe the effect of any changes.
Also, fitting a sine filter between the VFD and motor will reduce the effects of motor noise but it sometimes just puts it into the sine filter. We had an issue in a theatre once where a motor was too noisy. Fitted a sinefilter and cured the motor noise but moved the noise to the filter. We had to make sure the filter was sited well away from the stage.
Another point: cooling tower motors are usually the cheapest of the cheap motors. Could it be the bearings?
RE: Motor Whining
They had 2 x 250HP closed loop PDL vector drives, but it turned out the motors were only 160kW, so I turned on their "Whisper Wave" feature which varies the carrier frequency within each cycle as skogsgurra mentioned. I had to derate the drives a little as sed2developer said, but they were over sized for altitude to begin with and I figured they are only operating in winter when it's very cold, so it wasn't going to be a problem. The noise disappeared (to us Homo Sapiens at least) and I was a hero.
Of course, I made it out to be a much more involved process than it was. One must never pass up the opportunity to look good!
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Motor Whining
Gunnar Englund
www.gke.org
RE: Motor Whining