Maximum vibration on 100 kW DC motor

[ebarba]

Hello all,

A 100 kW DC motor has been moved from its original place (anchored to the floor) on board a centrifuge which now is mounted on air springs and vibrates.

The motor runs at 1000 rpm the transmission lowers the load speed to 330 RPM. RMS vibration velocity is 1.4 in/s. The motor is not the cause of the vibration, rather it suffers it, the source is the machine itself.

Is this too much? Using the vibration severity chart of course it qualifies for "stop it right now", but that chart takes into account that the motor is the cause of the vibration. This is a perfectly balanced motor riding on a rough machine... and it has been working well for the past 3 weeks (about 30 total hours of operation, each batch lasts 5 minutes and the process 24 batches a day).

I attached a photo of the motor and part of the machine.

Thanks!

 

[itsmoked]

Really? 100kW? Looks from here like maybe 10kW? Size will matter in the response.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ebarba]

It's rated up to 100 kW, but I think they downrated it to 75. Maybe the picture doesn't help, but to give you an idea, the rollers being driven by the motor are 550 mm in diameter and the motor is more than 900 mm long.

 

[Skogsgurra]

1.4 "/s is a lot!

I would look at the commutation when the machine runs at maximum load. Such high vibrations may/will cause bad commutation.

I would also make sure that the cables are not broken by the vibration.

I would tighten and perhaps lock the terminals with an extra nut. No LocTite!

And, finally - I would make sure that there's a spare motor available.

If the machine is important, I would consider an AC drive. Induction motors are much less sensitive to vibrations and need much less maintenance.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[ebarba]

Gunnar,
[ul]
[li]Cables have been fastened properly to avoid excessive movement and they are rated for mobile applications[/li]
[li]Terminals have double nuts[/li]
[li]There is a spare motor[/li]
[/ul]

Until now, no commutation or other electrical problems have been met.

The question is how long this can last... Unfortunately, floating suspensions for the motor are out of the question, as well as moving the motor outboard, as the transmission would get very complex.

We have already suggested to the customer to switch to AC drives, but it doesn't seem to be something they want to consider.

There is still a procedure we can deploy: tuned mass dampers, but on such a large structure we'll need many of them and tuning the system would become a nightmare. We won't do this unless absolutely necessary.

Thanks!
Ernesto.

 

[Skogsgurra]

OK, you have done everything that I could think of. Very good! And you have a spare motor.

Then I think that you should let Mother Nature provide the answer. If the thing lives through the first years - then I think that proves that the motor can withstand the vibration level.

If the motor dies after a few months, I think that the AC road will seem more attractive. Tuned dampers? No, that's for academia. Not for Real World Applications. And - doesn't a damper reduce vibration? The effect that the motor is supposed to provide in the first place?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Skogsgurra]

Sorry, I understand better now. The motor is NOT supposed to provide vibrations. Then, maybe dampers. But I would just let it run and prove/disprove itself first. Just make sure the customer understands the what and why (and the costs involved).

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.