AC Elevator Drive Audible Noise Help Needed. 6

[scmguru]

We've got a Geared Elevator Hoist that is being run by an Imperial AC VVVF Motor. The Motor is rated @ 1164RPM and the Gear Ratio of the Hoist is 87-2.

About a month after this piece of equipment was installed, it began making a hollow droning sound that is at least 18db louder than the AC Hoist itself.

I recorded the elevator hoist running and captured some WAV file snapshots of the change in waveform.

There is a very obvious and distinct change in the soundwave when this droning begins. I have posted a visual snapshot of this waveform here..

http://onfinite.com/libraries/850891/6ce.jpg

Over the last few months it has become worse and worse and we cannot seem to figure out what it causing it.

I have figured out that the sound is sinewave shaped and it peaks at about 330-338 hz.

I have a recording of an elevator run and this sound

T+0- Elevator Start - Normal Sound
T+9.5s Droning Begins
T+10.5s Droning Peaks
T+12s Droning diminishes
T+15s Droning comes back
T+16 Droning Diminishes
T+17s Droning comes back and doesnt come back
T+24s End of Run.

I would be happy to provide a screen video of this waveform (about 30 seconds) if anyone could give me any help with this.

This is a really serious problem for our building and its residents and our current vendor refuses to acknowledge any kind of problem.

 

[scmguru]

Also, just a heads up.. the Drive is an MCE AC-PTAC with a Yaskawa G5 GPD515 Drive

 

[Skogsgurra]

Hi scmguru,

Is this going down or going up?

Is there any difference between unladen car and fully laden?

Gunnar Englund

http://www.gke.org

 

[scmguru]

Gunnar,

Yes. There is a difference. It is worse when an empty car is going down, or a full car is going up. (Seems to be load related)

Michael

 

[scmguru]

Our vendor keeps telling me it is "normal" AC Motor noise, but i know enough to tell the difference.

Also, I have noticed that when the car is run on inspection (slower speed?), with a couple of people in it, the noise is virtually non-existent. You really have to listen for it (i.e. put your ear on the hoist)

 

[Skogsgurra]

OK, that makes sense. The counterweight is usually balanced so that the load is neutral when car is half. Going down empty is actually hard work. And going up full is also hard work. I think that you can exclude the gearbox since the wheels are engaged on different flanges when going up and down with empty/full car.

Gunnar Englund

http://www.gke.org

 

[scmguru]

Gunnar,

We did have a consultant out this week who looked at the main gear on the hoist, he indicated the pinion gear seemed to be wearing well into the ring gear. He did notice the "half-moon" wear pattern looked a "little" high (towards the outside edge of the tooth), but didn't feel like it was a big deal.

The history of this started when the lift was installed a year ago.

For the first month (at least) the lift made no noise, since then the noise started and seems to have become significantly louder/worse over the last 60 days.

 

[itsmoked]

Are you saying the noise is coming from the gear box?

Or you aren't sure?

Keith Cress
Flamin Systems, Inc.- <

http://www.flaminsystems.com>

 

[Marke]

Hello scmguru

Is it possible to alter the speed that the hoist operates at by a small percentage, i.e. slow it down by say 10% and see if there is any change. It is possible that there is some form of resonance going on here.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[scmguru]

Keith,

We're not 100% sure but thats what it seems like..

Mark,

I'll see if I can get my vendor to slow the lift down. I do know that when it runs in "inspection mode" which is considerably slower than full speed, the noise is reduced by 80%. If you REALLY listen for it, i.e. put your ear on the hoist or on the cement posts surrounding it, you can hear it but not from many feet away. Full speed, the noise is totally airborne and can be heard from 1-2 floors away.

 

[itsmoked]

Is there any chance you could put a microphone on the gearbox so you could judge whether the sound is loudest there as that would confirm it as the source. The rest of the structure might be 'sound boarding' it and hence sound noisy too, but if it is loudest at the gear box I would start making assumptions it was the gear box.

You could either place a small digital recorder right on the gear box or one of those cheap "spy bugs" tuned to an FM radio channel so you can hear what's hitting the microphone directly while standing anywhere.

You can then move your sound pickup to the rails or elsewhere to confirm which is louder.

Keith Cress
Flamin Systems, Inc.- <

http://www.flaminsystems.com>

 

[jraef]

Can you tell us what operating mode the VFD is in, i.e. V/Hz, Sensorless Vector or Flux Vector (with an encoder feedback)? If anything but Flux Vector, there are some features in Yaskawa drives that could be causing this if improperly set up.

For instance, if in Sensorless Vector mode, it has 2 features called AFR and ASR (Automatic Frequency Regulation and Auto. Speed Reg.) that can cause "hunting" of frequency if set up for one type of load, but then used with a different one. The hunting can be tuned out, but it won't take care of it on its own.

If in V/Hz mode, it has an Anti-Hunting feature, that if over tuned when unloaded can cause vibration when loaded, which would decrease with load.

Just a thought.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[waross]

Just a thought.

Quite a good thought, I thought.
scmguru, Can you determine if the sound is originating in the motor or the gearbox?
Am I correct in supposing that frequency hunting in the motor can lead to stresses in the gear train that may cause the noise to be generated and possibly amplified in some other mechanical member, even though the motor may be responsible?

 

[scmguru]

jraef- Open Loop Vector.

 

[scmguru]

jraef- There is an encoder on the end of the imperial ac motor and it is hooked to the controller/drive.

 

[DickDV]

I would change the carrier frequency of the drive upward and check for the new noise level. If this changes the noise level or pitch, you are getting the typical squeal that results from PWM pulses exciting the magnetics in the motor.

If the pitch or level changes with carrier frequency, you may want to add a dv/dt filter or even a sine filter between the drive and the motor to quiet the motor. I doubt if a simple inexpensive reactor would do the job.

If, on the other hand, there is no change when carrier frequency is changed, the noise is likely mechanical.

 

[jraef]

With an encoder, I'd say is was in Flux Vector mode. Maybe that's the problem. If the design was for Flux Vector, but someone reprogrammed it for Open Loop Vector, then they would have also needed to tune the AFR and ASR, because in Flux Vector mode that would not have been necessary, so it would not have been done.

You're right waross, that was what my thought was. The hunting of the drive as it tries to find the right level, or the pulsation caused by it overcompensating for a different load, is being amplified mechanically by or through the gearbox / mounting system. A strictly audible whine from a PWM drive would not transmit well through concrete posts and then retransmit through air for 1 or 2 floors of a building. This almost has to be a mechanical harmonic.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Marke]

I think we are all coming to a similar conclusion. I suggested dropping the actual frequency as this would probably change the characteristics if it is a loop situation, but make little difference if it is a gearbox issue. - should be very easy to do.

Best regards,


Mark Empson

http://www.lmphotonics.com

 

[scmguru]

I think it's got to be mechanical.. AC Motor Area, no droning, just AC motor noise. Brake area, no droning.. Area where worm contacts ring gear.. bingo. Going down to the end of the hoist @ the bellhousing, little to no droning.

The loudest section where the droning/humming is coming from the area around the outer bearing supports.

Our consultant noted on his report that the teeth on the ring gear seem to be developing a nice 1/2 moon even pattern but it looks a bit "high" on the tooth. Mentioned something about "lowering" the ring gear for better tooth contact?

 

[Marke]

Hello scmguru

You could be right, but if there is some highspeed instability in the "system" loop, it would reflect as noise from the gearbox. To put it another way, there is possibly some loop oscillation that is causing a pulsing torque rather than a smooth and constant torque. This could cause the gears to be loaded unusualy and may cause additional wear on them.
I would expect that if it was a gear isue, that the oscillation would be present at all speeds. When I look at the data, it appears that the oscillation only begins when the drive settles to run at constant speed. During acceleration, there is no issue. I believe that this is significant and points to the drive or speed. The drive could develop an oscillation that could be speed dependant, so dropping the speed may overcome or change this, or the drive may not have been set up correctly, for example set for open loop vector with an encoder or wrong parameters etc.

Best regards,

Mark Empson

http://www.lmphotonics.com