We have face a very critical situation regarding the vibration in a Gas Turbine CENTAUR 40 model by Solar Turbines.
Before explanation of the nature of the vibration, I share the machine design data for reach the root cause.
1. 11 Stage Axial compressor.
2. 15015 RPM of the Turbine engine.
3. Two shaft Gas Turbine.
4. There are 3 tilt Pad bearings on turbine engine side.
5. First critical speed about 28 % and second critical speed at 56%.
6. OR36 with NVGATE and Vibroport 41 is used to capture the FFT or Time wave forms. There is no option in the turbine for phase analysis.
Now i explain the fault for diagnostic.
When the turbine start every thing is going fine. No High vibration found at any frequency.
When engine reaches at 87% the Peak at 2X is going to increase while 1 X is not increasing and 2X reaches at the alarm value as speed increase but 2 X goes down when engine achieved 92 % RPM. It means the vibration found high between 87 to 92 % RPM band and just on the diffuser section where bearing # 2 found.
On the other hand the vibration on bearing 1 and bearing 3 is well with in limit.
Here i attached some data in picture format which helpful for discussion.
I describe the file name and their detail
1. GP-V and GP_H.JPG shows the spectrum during 87 to 92% band.
2. SKID_SPECTRUM.JPG shows the FFT at skid base.
3. support_FWD.JPG shows the FFT at support FWD side of the engine.
File 2 and 3 FFT taken to check the soft footing and looseness.
The other is the view of the diffuse section where velocity probes are attached.
Here is also attach a Time wave form get by cross chanel.
One thing i observe this vibration is also occur at deceleration at the same band.
also if i stay the engine between this band for 6 to 10 minutes the 2 X peak starts to goes down but still high.
If more data required please feel free to ask and advise me how i fix it?
GP_H means Gas producer Horizontal, and GP_V means at vertical.