Remnant speed after GP steam turbine trip valve closes

[Wkcoo]

Hi community, would like to find out more about your experience about how much remnant speed is acceptable after GP steam turbine trip valve closes. As an example, the steam turbine does not stop completely due to trip valve has leakage or the trip valve is not a tight shut design. Any rule of thumb of the acceptable limit such as 10% of rated speed etc.

Appreciate also if you have experience in calculating and establishing the speed limit for trip test acceptance.

 

[SB1976]

Hi,

Slow roll of Steam Turbine can be as low as 5% of the Max Rated Speed, if that's what you are looking for. This speed is dictated by machine's lubrication system capability.

Lube oil (LO) System for Steam Turbine is usually equipped with shaft driven main LO pump along with electric/separately driven auxiliary LO pump. Main LO pump works during machine operation while auxiliary LO pump operates intermittently (during start-up and shutdown scenarios). In your case, in the event of machine tripping, the shaft driven main pump cannot deliver the required flow and pressure and hence the auxiliary pump kicks in to avoid overheating of the bearings. So, the slow roll speed of the ST corresponds to that speed at which the lube oil system can support.

Trust this clarifies.