Generator Humming Sound

Greetings,

We have a 7FA generator with humming sound. metal temperature of bearing is not high, so I think the problem is not from bearing clearance. can you share whatever information you have about it?

Note: unit is running since 2-3 months with this problem, and waiting for the scheduled outage to diagnose the problem.
 
Greetings,

I forgot to say that there were no vibration detected by the two vibration measurement devices.
 
Any ideas? It is not the same sound as the one found in transformers
Actually the sound gives you a feeling like something is shaking.

>I forgot to say that there were no vibration detected by the
>two vibration measurement devices.
 
Thank you CSA,

>It definitely sounds as if something is loose; possibly stator through-bolts?

>Hope your outage is soon.

yeah, it is not far.

Hopefully, I will provide you with the feedback.
 
Hello.

To update you on the this topic.

GE recommended (as a first step) to inspect the belly band + the key bars. I believe the key bars hold the lamination in place while the belly band support the key bars.

We have pulled the coolers (HXs) from their place and entered the generator from the other side to inspect the keybars + belly band. the cooler is around 3.2 meters long.

After doing the inspections we found the followings

1- Sign of key bar movement (because the color of the key bar was wiped off in one area. I believe it is because the key bar moved axially and scratched against the belly band).

2- Red Iron dust under the cooler

3- Sign of belly band segment joint misalignment.

4- clearance between the key bar and belly band reached around 20 thou in some locations ( According to my knowledge, the max. allowable clearance is 2 thou).

these are our findings, I will update when there is a progress.

Thank you
 
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