Have a puzzler here. We just did a short outage on one of our units. I was to check lift on our ID fan bearings. Unfortunately got pulled to replace transducers on a PA fan, so didn't get to see lift inspection (someone else did it). After start up I was called to take data on the motor (high vibe from Bently rack). We I went to take data I noticed there was a definite thump going on in the motor that wasn't there the last time I collected data. This is a massive motor so the plots I will try to attach do show, to me, high readings. The peaks are 1X ts and harmonics verified with time syn avg. Looks like either bearing clearance or rotor rub. Like I said you can physically feel what seems to be a once per rev thump in motor. Hope this goes through. I will try ans post TSA plots also.

2a_id_fan.rtf (191 Kb, 58 downloads) 2a ID fan vibe

Roy,

I assume we are talking about journal bearings. Does the Bently rack connect to proximity probes, and if yes, did you do any analysis from the Bently rack? What maintenance work was done during shut down?

I suppose that you could have a rotor rub, but I wouldn't characterize the sound or vibration as a "thump", so I doubt it. The waveform indicates the thump is at 1xSS, but there is a lot of harmonic content indicating a sharp impact and not a gradual rub. Assuming that the bearing oil level and color are normal, then I would look for axial bumping of the rotor against the thrust collars or poor coupling condition (assume it is a gear-type). You could check rotor axial position with a strobe light or shut down and break coupling loose to verify rotor center position and inspect coupling.

Walt

Roy,

Do you have the "before" seismic data on the motor? You did not post time waveform data to substantiate an impact. The spectrum pattern does not necessarily point to an impact. Also any Bently data will be helpful.

Walt and David sorry for taking so long to reply. David Will try and post waveform data. Walt no gear coupling it has a "rubber insert style" If memory serves me right from fall outage inspetions there are @15+ solid rubber tubes in the coupling. Haven't seen any bently data they just collected it today. I would like to hook my 2130 up to the prox probes but have never done it before. Never had to deal with journal bearings at my former place of employment. Do I have to use any special gadgets or setup for the 2130 to utilize existing probes. Any input is deeply appreciated.