VFD Ringing noise
We have a 50HP 460vac Siemens VFD powering a Vfd rated 50HP 3600RPM motor. The system has been running fine. Recently the motor started making a high pitched ringing noise. The current draw is 35, 35, 32 Amps at the motor. The Voltage to the drive is 455, 456, 455Vac. One leg is 3 amps lower. The motor leg resistance is .2U .2V .2W
What could be causing the ringing noise? Why is one leg pulling less I than the other 2 legs? Thankyou
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I would not think that this difference is cause for great concern, this may be due to slight differences in motor/drive characteristics, but if the ringing just started, it may be something has changed in the drive and a sign that future problems may appear.
Many VFD's have the ability to change the switching frequency, sometime bumping it up to a higher value gets rid of the ring.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
It might also be that the windings in the motor have started to loosen up a little, allowing the carrier frequency to move those windings more and generate the noise. I've also found some manufacturer's line reactors ring worse than others even when brand new.
Be aware that bumping the carrier frequency up causes more heat loss in the drive and some models must be be derated if used at higher carrier frequencies. This seems to be getting more common as package sizes shrink and they start squeezing more of the overhead out of the design. I've seen newer models from the same mfg require upsizing the drive to run an existing motor. The older drives were simply rated for more current output for a given (hp, kva, kw) than the previous generation even at high carrier frequencies for the old versus low for the new. Also, if you raise the carrier frequency watch for electrical noise issues if you have photoeyes, proximity switches or other devices nearby. If the motor leads aren't shielded they can sometimes cause erratic operation of those type devices. Low carrier frequencies can help alleviate those issues.
But as Al said, it could be a sign of impending failure. As for the lower amp draw on one leg, try reading at various places and orientations if you are using a clamp on ammeter. They can be influenced by the other legs.
As an aside, I once had a clamp on "lock" onto a cable due to the high current flow through the cable. It's been a long while back on a very large drive but I think it was on a DC bus lead. I had to get a guy with really strong hands to get it off as I couldn't stop the drive just to get my meter off.
One leg of Drive output has a different Freq than other 2 Legs. Example: U=600HZ V=600HZ, and W=400HZ. The deviation is linear. I checked the IGBT's and they appear to be OK. Checked Analog components on Control board and they two appear OK. ANY Idea's?
How was this measured? If using a frequency counter, it could be a harmonic?
I would expect the fundamental frequency to be the same, or did you 'scope it?
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
I used my current clamp meter with frequency capabillity. Should I use my scope for better acuracy>
Probably be interesting to see the actual wave form on a 'scope, and get the true picture.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
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