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Regarding turning gear: how long interval after stand still before start up? because this unit always got high vibration if start from stand still

txs

I found this thread while searching for something else. Maybe it's kinda long when it was posted. However, at least my 2 cents could be something for some1 else. ;)

Turning gear must be engaged when the steam turbine speed drops to 0 RPM. Usually the turning gear motor will run at about 20-30 RPM and the clutch will engaged when the speed reaches 0 RPM. In case the turning gear failed to engaged after reaching zero speed, quick action needs to be taken to ensure that it is engaged. If all the measures fail, manual barring should be done immediately (seriously, it's damn hard. ;) ).
However, worst case scenario, should everything fail, the turbine should be put into standstill for a period of at least 3 days (usually) until the wheel space temp reaches nominal value (avoid uneven cooling).

Bear in mind that rolling the turbine during this kind of situation will cause serious rotor bow condition.

P.S.: Maybe the originator's machine has some level of rotor bow already, which is causing the high vibration. ;)