High Gas Turbine-Generator Vibration GE Frame-9

A power generation company in Oman was facing high vibration issue in one of the GTs. At Full Load of around 100 MW, the turbine was vibrating at 9.63 mm/s PK (velocity sensors). This is near the set alarm of 11 mm/s PK, and there was a chance vibration would increase during peak summer.

GT CCR DATA WITH HIGH VIBRATION

SITE CONDITIONS

• The machine train consists of a generator (120MW Base load capacity) Turbine and Generator operating at 3000rpm. The GT is mounted on a concrete foundation.

• High vibration was observed mainly on Generator DE  (Bearing 5).

• Major overhauling was done on the Turbine (Not Generator) three months ago.

• No proximity sensors available.

OBSERVATIONS

• The initial data were taken on the Generator NDE and DE show dominant 1X and minor 2X.

•  The higher-than-normal 1X is due to unbalance force on the Generator.

• Other bearings showed normal 1X within acceptable limits.

• The run-up data of B3 and Generator DE Shows two critical speeds, 1st at 1,100 RPM and 2nd at 2,108 RPM.

DIAGNOSIS

• Since the high vibration was observed at 1X speed with a phase angle of 114 Degrees (Vertical to Horizontal), the cause of the high vibration on the Generator was identified to be caused by unbalance.

• On-site balancing could be done to reduce the vibrations.

VIBRATION SPECTRA FROM GT BEARING

ACTION PLAN:

• Inspect the Generator rotor.

• Carry out on-site dynamic balancing.

MAINTENANCE:

• Inspection of the generator rotor revealed a high quantity of dust deposition on the rotor.

• The dust had solidified on the rotor and could not be easily removed.

• Since the tools were not available for proper cleaning at the site, it was decided to carry out dynamic balancing as a short-term solution.

• All the air inlets and filters were checked and minor faults were corrected. Some leaks in the filter house were also fixed.

Generator rotor with dust deposits

ACTION:

• On-site dynamic balancing was carried out to reduce the vibrations significantly

• Preventive measures taken to prevent further dust deposition.

• A plan was put in place to clean the rotor during the next outage (will require removal of old balancing weights after)

GT CCR DATA AFTER BALANCING

Vibration Data from GT Set, Before & After Balancing