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Siemens V94.2 Gas turbines have jacking/rotor lift oil pumps which operate while machine is on turning gear. But GE Frame9 gas turbines have no jacking oil pumps? Some people say that it is because of their design. Can someone please explain this in detail?

Thanx

What do the other people say the reason is?

Because the some people are correct; it's just a design philosophy, in conjunction with the types of bearings used on the turbines and/or the generators.

And, you are partially incorrect, because GE F-class Frame 9 units do have jacking oil (or, lift oil) pumps.

Jacking, or lift, oil pumps are used to decreases the amount of torque required to break the shaft away from zero speed during starting and/or to decrease the amount of torque required to maintain turning gear, or cooldown, speed. Some bearing designs, such as tilting pad bearings as opposed to journal bearings, require more torque at low speed operation, such as during acceleration from zero speed while starting or during turning gear, or cooldown, operation.

Some GE Frame 9Es have generators (Brush generators, I believe) which do have jacking, or lift oil, pumps. But not generally the turbines.

Personally, I'm not a fan of jacking oil pumps. They are usually AC motor-driven, non-redundant, and have no DC motor back-up, so that if the plant were to be blacked out and the unit tripped or the plant blacked out while the unit was on turning gear, or on cooldown, the shaft will come to rest and can not be put on turning gear or maintained on turning gear, or cooldown. Which means the rotor will bow slightly, which can usually be taken care of, but not for many hours depending on hot the shaft is.

Also, they are just another auxiliary which can fail or malfunction, and I like simplicity because it usually leads to reliability.

But, just like design choices, these are my personal preferences.

Thanks CSA for your explanation. But I want to know few more things. I am mentioning here GE Frame9 (MS9001E) GTs & I don't know much about other models.

Now, difference in designing? Siemens v94.2 GTs have four bearings & GE Frame9(MS9001E) have 5, is this a difference? Do adhesive properties of lube oil used make a difference?

I have heard that because of design (or may be because of lube oil properties), oil film around shaft(general) devolps only at 2 rpm for Frame9(MS9001E) GTs?