Vibration on Turbine Generator 12.5MW, 13.8KV, 1800 RPM

Think about this for a moment.

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There. You done thinking?

That size turbine/generator was probably custom made for your requirements. with a design factor that included ambient temperatures of air and coolant liquid, as well as normal heat output from the generator itself. If it gets cooler than the design parameters, shrinking components allow increased tolerances beyond the design limits. Hence vibration. With that not inconsiderable mass, I can imagine your concern.

Next time, think about it, or Google it. Then come here for confirmation or enlightenment.

Namaste'

it is dynamic equilbrum

Further information is that - No vibration if we could run air inlet temperature above 46Deg C. even 60Deg C no vibration, the vibration starts only if we come down to below 43Deg C.

How the problem started ??History shows that once alternator shaft seal leaked and bearing lube oil flashed over the rotor and also the oil got accumulated into the alternator. the same removed and cleaned in place. on start vibration problem noticed and the same controlled by maintaining the air inlet 46 Deg C and above, the equipment was used in this condition as the load demand was always 10MW and was very easy to keep the temperature above 46 Deg. but had a problem on every startup during cold start. operator use to keep the cooling completely close and run the turbine alternator to warm up and bring the temperature to above 43 Deg C and put on load for increasing further and ran like that. Am I confusing too much!!!!!?????????

later few years of operation with the above condition, we happened to rewind the alternator as this alternator got burnt (not because of vibration). rewinding is done at site using resin rich coil winding instead of factory winding vapor pressure impregnation. with the resin rich winding the nature of winding is expected to operate atleast 10% above temperature range than factory VPI winding.

we deployed third party for finding the cause for vibration and arrest them. but no luck, still problem remain same.

few thought as of now

some says the bedding chockfast is damaged - yet to be checked, it is looks like chockfast is poored and one foundation plate is put on top and alternator is sitting on top of the plate

some says it is alighment problem, having proper alignment we can eliminate the probelems

some says there is problem with foot plane allignment, doing foot plane alingnment will resolve this issue.

need to find the correct problems.

Yikes! You did not run the generator on turning gear for 24 hours before spin up? That size rotor will develop a sag during down time, and must spend time straitening it out at about 3 to 6 RPM on turning gear. Bring your lube oil up to temperature while you are going through the flush cycle, then turning cycle, then spin up. But turn it for 24 hours or more. Re check your alignment and floating tolerances before anything else.

This 10 MW machine is in all probability air cooled with one cooler located on the convenient end. The air flow through the unit is probably pretty straight forward with the field fans taking suction from the end winding area and pumping air into the air gap where it would flow out through stator and into the rotor with some scheme to route the air into the inlet side of the cooler.

Usually when dealing with large generators 4 or more coolers are employed and a usual source of problems is encountered if the temperatures aren't balanced between coolers. You may be experiencing a similar problem if the field or stator cooling slots were plugged in a random fashion during your contamination incident.

This would give you an effect similar to thermal instability which is usually caused by shorted turns, but in this case would be because of a flow pattern not to design.