Dear All,
Recently we have carried out 15 MW STG set major overhauling and gear box. In gear box we have not changed any parts, but we only checked the bearing clearances, teet contact and back lash.
The high speed (7700 RPM) bearing clearance was found on higher side i.e. 0.53mm, however we didn't replace the bearing due to non availability of the same. After box up we have started the machine and synchronised.
At FSNL and FSNL with excitation no all the bearing vibrations in complete train was normal, however when the STG was loaded beyond 3 MW we saw gear box high speed side drive end vibration reaching to trip level.
But after load was further rised beyond 4 MW the vibrations became normal. We had run the machine at 12 MW load for almost 12 hrs and saw no major changes.
To check the phenomenon again we have reduced the load to less than 4 MW and we saw similar phenomenon of high vibration observed in high speed side drive end. During this period the turbine rear end vibrations were normal. To overcome the issue we stopped the machine and rechecked the alignment and further fine tuned the same.
After correction when we started there was no change found in vibration in 3 to 4 MW zone. Now the machine is running on higher load without any problem.
Now my question what are the probable reason for this phenomenon.
Recently we have carried out 15 MW STG set major overhauling and gear box. In gear box we have not changed any parts, but we only checked the bearing clearances, teet contact and back lash.
The high speed (7700 RPM) bearing clearance was found on higher side i.e. 0.53mm, however we didn't replace the bearing due to non availability of the same. After box up we have started the machine and synchronised.
At FSNL and FSNL with excitation no all the bearing vibrations in complete train was normal, however when the STG was loaded beyond 3 MW we saw gear box high speed side drive end vibration reaching to trip level.
But after load was further rised beyond 4 MW the vibrations became normal. We had run the machine at 12 MW load for almost 12 hrs and saw no major changes.
To check the phenomenon again we have reduced the load to less than 4 MW and we saw similar phenomenon of high vibration observed in high speed side drive end. During this period the turbine rear end vibrations were normal. To overcome the issue we stopped the machine and rechecked the alignment and further fine tuned the same.
After correction when we started there was no change found in vibration in 3 to 4 MW zone. Now the machine is running on higher load without any problem.
Now my question what are the probable reason for this phenomenon.