Due to some reasons the load over one of the STG increased from 15MW to 25MW, no major change observed in Generator & Turbine online & offline vibrations
But the single stage reduction GB (6300 rpm to 3000 rpm) showed high increase in offline vibrations i.e from 8 mm/s rms to 13 mm/s rms, but the shaft vibrations were not having any change i.e 30 microns
Turbine rpm:- 6300
Generator rpm:- 3000
No. of teeth on high speed shaft:- 37
No. of teeth on low speed shaft :- 78
No. of teeth verified from GB data sheet & name plate on GB
Sidebands for 3000 rpm also present in FFT
The FFT shows harmonics of 72242 which i am not able to correlate with anything in the GB ( i might be missing something), also there is no GMF peak in FFT. (MY Fmax is 8lac)
Note:- there are 3 similar STGs all having the same FFT spectrum in their GB, however they are running at low vibration amplitudes.
Is it possible that a GB does not show GMF??
What is this 72242??