Dear sir,

I have a question. if i have the DC lube oil pump running, it will prevent the hydraulic pump to start? why?

My turbine is GE 9fa.

Thank you

 

Have a look at your L.O. and Hydraulic P&IDs and you should find that the hydraulic pump suction is "fed" by L.O. pump discharge; in other words, the hydraulic pump does not take its suction from the L.O. reservoir but is pressurized by L.O. pump discharge pressure.

The Emer. L.O. pump (DC motor-driven) is only intended to supply the bearings during coast-down when L.O. pump pressure is insufficient. In my estimation the philosophy would be that drawing additional oil from the discharge of the Emer. L.O. pump to supply the hydraulic pump would possibly reduce the bearing supply during Emer. L.O. pump operation.

Also, a review of the P&IDs may even reveal that the discharge of the Emer. L.O. pump does not provide pressure/flow to the suction of the hydraulic pump. There is a pressure switch on the L.O. pump discharge used as a permissive to run the hydraulic pump so if there is insufficient pressure the hydraulic pump should not be able to start--this to protect the hydraulic pump as it is a positive displacement pump and requires a net positive suction head (provided by L.O. pump discharge).

Again, have a review of the L.O. and Hydraulic System P&IDs and I believe most of your questions will be answered.

 

Thanks for your reply.

Uhmm, I know i will have the turning gear motor locked if i lost the lift oil pressure.

But i want to know it will be locked due to over lube oil temperature? Why?

My turbine is GE 9Fa, MK VIe, DLN 2.6+

 

There seems to have been some kind of event that you are trying to understand.... If you would just describe the event and possibly provide some additional details that might be requested we might be able to help.

But, let's just think about lift oil pressure and oil temperature and a starting motor permissive. I'm having a very difficult time relating the three. It's conceivable that if there were no lift oil pressure the starting means would be prevented from starting the turbine. And if the lube oil temperature were excessive the turbine would be tripped and prevented from starting. But that's a pretty odd group of occurrences that would suggest some unusual operating circumstances if all occurred at the same time.

And how does this relate to running the hydraulic pump when the DC Emer. L.O. Pump is running?

Without being able to see the application code running in the Mark VIe it's virtually impossible to say. The Belfort Bunch have been doing some very unusual things with their logic.

This is an odd thread, to say the very least.

 

Thanks for your help,

And i hope that i didn't disturb you by these abnormal operational situations.

 

amr karam,

You're welcome. When I get unusual questions like this it's usually the result of one of two things; first, some event occurred and people are trying to understand how it happened or understand how they should have responded to the event. Usually, the questions are very "leading" because the questioner is asking the question(s) in such a way as to get validation of their understanding/explanation of what happened. They purposely don't provide all the details and evade pointed questions, again in an effort to prove their theory/explanation which is incorrect.

The second reason for such questions is that the questions were asked during a job interview or a promotion review process. A lot of times if the question is a multiple-choice question the test-writer may just be making up answers without any idea of relativity--which sometimes makes it easy to eliminate the choice(s) to choose the most likely correct answer.

I note also that the 'Subject' of this thread changes in the subsequent exchanges, probably because the direction/focus of the questions changed so drastically. Usually, it's best to start a new thread when the subject matter changes; simply changing the 'Subject' doesn't open a new thread. Many people read these threads over time (more than a decade now since the GE-design heavy duty gas turbine controls-related community has flourished here at control.com!) and they usually view the 'Subject' when looking for a particular explanation or problem, so changing the topics so drastically can prevent people from finding relevant information when searching the "archives."

So, it would be great to understand how these questions came to this forum--not essential, but informative. And, it's most helpful to others to keep the topic close to the original subject, or to open a new thread when a new topic comes to mind.

That's the source of my confusion--not understanding the context of the questions, and the different direction of the questioning. I usually find that when I understand the context of the question I can respond better, quite often providing useful information that would otherwise not have been offered.

 

You may want to look at your GE 9FA package AS-BUILT P&ID.

Then you may want to verify what is the objective(s) of your DC Lube Oil Pump - obviously the DC Lube Oil Pump is furnished to supply minimum lube oil to all bearings for the machine train when emergency...no power supply to continue operation of the machine train; basically you will shutdown and coast-down.

Once your DC Lube Oil pump cut-in, it will supplies the minimum oil flow to bearings for residual heat removal within the bearing housings.

With all means, the priority to have all lube oil that the DC Lube Oil pump can delivers at that time (to cool down bearings) is to protect stagnant heat at babbitt metal. A little bit of oil adequately to carry away the residual heat overtime until you restore the main power supply to AC Lube Oil Pump(s).

Then, back to your original cross-question : Why DC Lube Oil when it is running, you can't run the hydraulic pump...

Well, referring back to check the P&ID just now, the objective of your hydraulic pump(s) - I assumed (I don't know how was you GE 9FA being configured) but in front of me is MS-5002D P&ID, I assumed the hydraulic pump(s) are meant to slow roll the Gas Generator rotor as one of the primary design intent.

If you on emergency shutdown, you can't do much...because I think, for heavy rotor, you need a jacking oil pump to lift the heavy rotor, then the rotor will be lifted, the ratchet able to be activated and slow roll the turbine rotor, at the same time ( I assumed to do this you need enough lube oil supply to separate and lubricate the rotor journals and tilt-pads bearings)...then these pre-requisite must be lined-up so that, you can run your hydraulic pump...the DANGER...if you run DC Lube Oil pump, AND Hydraulic pump...you may scored your journal(s) and wiped off your babbitt metal surface due to insufficient oil...

Trust these provide you some idea(s).

 

Have a look at your L.O. and Hydraulic P&IDs and you should find that the hydraulic pump suction is "fed" by L.O. pump discharge; in other words, the hydraulic pump does not take its suction from the L.O. reservoir but is pressurized by L.O. pump discharge pressure.

The Emer. L.O. pump (DC motor-driven) is only intended to supply the bearings during coast-down when L.O. pump pressure is insufficient. In my estimation the philosophy would be that drawing additional oil from the discharge of the Emer. L.O. pump to supply the hydraulic pump would possibly reduce the bearing supply during Emer. L.O. pump operation.

Also, a review of the P&IDs may even reveal that the discharge of the Emer. L.O. pump does not provide pressure/flow to the suction of the hydraulic pump. There is a pressure switch on the L.O. pump discharge used as a permissive to run the hydraulic pump so if there is insufficient pressure the hydraulic pump should not be able to start--this to protect the hydraulic pump as it is a positive displacement pump and requires a net positive suction head (provided by L.O. pump discharge).

Again, have a review of the L.O. and Hydraulic System P&IDs and I believe most of your questions will be answered.

Can you help me understand why OEMs specify a DC motor with associated DC starter? Surely its a simper solution to have these motors/drives on a standard 3ph 400V distribution with an induction motor ( If for example its fed off a essential supply that is UPS backed ). Having to create a separate 110V DC supply/distribution always seems daft to me.

 

If you can have twin AC with a capability to run everything from either supply but it is an expensive fix. DC is simple and cheap and reliable