Generator High Vibration 1

[bluemax]

The generator goes into high vibration(10 mils) after being at running speed for 1/2 hour prior to synchronizing, does anyone have any ideas as to why? This is a steam turbine generator set. Vibration starts at 1 mil and goes to 10 mils quite quickly.

 

[byrdj]

a Rub.
Was the unit just inspected and re assembled. Is the phase angle rotating when at constant speed.

Oil whip
is oil temp a little cold (or bearing elavation change during inspection. at what frequency is primary mode. Oil whip primary is near 1/2 rated speed

wiped bearing
was there a temp spike in bearing metal temp during previuos coast down.

What type of unit
If you have LP hoods, running at noload will heat the backend and cause the rub. a cooling spray nozzle could be pluged causing uneven heating

 

[byrdj]

Put it on gear for 4 hours and try again

 

[sms]

Is it in the generator or the drive? Hydrogen cooled or air cooled.

Assuming that the vibration is in the generator not the turbine:

The main question is what is the vibration frequency?

If it subsynchronous, it could be misalignment between the turbine and generator unloading the generator inboard bearing.

If it is 1X and in the generator, it could be a rub, but rubs are pretty unusual in generators. Does it happen when you flash the fiel? Could be a hot spot in the exciter. I saw one once that would go to 10 mils pp immediatly on flashing the field, even before any load was applied.

"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[ScottyUK]

If it occurs some time after raising excitation then a shorted turn on the rotor is a good bet. The shorted turn causes asymmetric heating of the rotor which in turn develops a bend due to uneven thermal expansion of the forging. The vibration will correlate reasonably well with reactive load as the field current varies, but with a significant thermal lag.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[rmw]

When I read the OP I couldn't determine if the vibration ocurred prior to synchronization but after being at speed for 1/2 hour or if it was post sync but after having been spun at speed for 1/2 hour.

In either case, the rapid onset of vibration from 1 to 10 mils didn't lead me to suspect a rotor short right off due to the thermal lag mentioned by ScottyUK.

If it were 30 minutes after syncronization...............

rmw

 

[ScottyUK]

What is the rotor / casing differential expansion doing during the half hour period at sync idle prior to closing onto the grid? This is a critical measurement and should be closely monitored during startup.


----------------------------------

If we learn from our mistakes I'm getting a great education!