High frequency vibration in large Fan

[rai asif]

Trying to diagnose some vibration issues here in a large Combustion Air Fan with a VFD driven electric motor. Bearings are oil lubricated rolling bearings. Frame is rigidly bolted to a concrete foundation and properly shimmed. Rotating frequency is 3042 rpm maximum, and rated frequency of 2982 rpms.

During high load operation we had a high vibration of motor on axial side. The value spiked to 8 mm/sec where, horizontal and vertical vibrations remained below 2.5 mm/sec. The vibrations were higher on the motor side.
Does anyone have any insight here as to what could be causing this? Or any suggestions of things to check?
Thanks in advance for any suggestions!

 

[LittleInch]

What frequency?

A spectrum analysis is a big plus to try and work out what is happening.

Doe sit occur at the same VFD setting?

What do you mean by "high load"? Is there some sort of fan driven effect?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[rai asif]

High load means fan running at higher load i.e. 80% of the the speed.

 

[Strong]

Considering: VFD, high load, and high frequency (no spectrum or identified frequencies)vibrations, then the "fault" could be EDM surface erosion in one of the bearings.

https://www.bing.com/search?q=edm b...E12643AAA2AC4033BEBD7486&ghsh=0&ghacc=0&ghpl=

Walt

 

[electricpete]

> High load means fan running at higher load i.e. 80% of the the speed.

I'm not sure I understand. I'd think most vfd fan applications increase speed as load increases.

Either way, vib change with speed change COULD be resonance.

But one of many possibilities. Far too little information