This case study is about root cause analysis of high vibration trip of a GE 6B gas turbine power train. The power train operating in a power generation plant consists of a 6B Frame gas turbine, speed reduction load gear, and generator. During the normal operation of the unit at 33MW, the power train tripped on high vibration on load gear casing sensors, the vibration amplitudes crossed 1.4 in/s within 1 sec from a stable value of 0.25 in/s. Analysis of 40 millisecond trip log data indicated the root cause of high load gear vibration was hunting of a steam injection valve which is used for gas turbine emissions abatement. The hunting of a steam injection valve caused abnormal pressure fluctuations in the combustor section of the turbine, these pressure fluctuations caused oscillation in the turbine’s axial compressor discharge pressure resulting in partial rotating stall and momentary axial shift of the power train. This momentary axial shift of the power train increased the load gear housing vibration and led to high vibration of the power train.
The unit was restarted after correcting the steam injection valve hunting issue based on engineering recommendation and the vibration levels came back to normal.
1. Rotor vibration should be looked at system level.
2. Understanding of the turbomachinery accessory system is helpful to diagnose the vibration issue.
3. Sudden axial shifts/jerks will get translated into radial vibration response in gear boxes due to gear mesh.
Bio - Edward Michel
Raised in New Canaan, Connecticut. 20 years working for GE Power in Atlanta after graduating as a Mechanical Engineer from Georgia Tech. Currently balancing turbines and generators, resolving technical issues, and leading root cause analyses in Steam Turbine Product Service. My first four years at GE were in the Monitoring and Diagnostics Center, monitoring the GE fleet and diagnosing trips, and writing monthly customer reports. The next four years I handled compressor and vibration issues in the fleet as part of Gas Turbine Product Service. Then I spent two years as a Six Sigma Black Belt, improving processes for updating drawings, resolving customer issues, and enhancing technical depth. And before my current position I traveled the Southeast US for two years as a Machinery Diagnostics Engineer at Bently Nevada, a GE Company.
Bio - Kiran Vangari
I am a mechanical engineer with more than 10 years of experience in rotating equipment domain in Power and Oil & Gas industries working for GE. I specialize in condition monitoring and vibration issues troubleshooting, both hands-on in the field and remote guidance to field teams, of heavy duty turbomachinery such as gas turbines, steam turbines, generators, compressors, pumps, expanders, etc. I possess excellent innovative and analytical skills with 7 inventions and 1 patent publication in turbomachinery & vibration domain, and 8 analytics in vibration condition monitoring domain till date.