we are facing problem when off base AC motor fail DC comes in picture. Header become pr. OK, but warren pump temp 26Qt-3 & TT Qt-3 rising & machine trips. suspected SOV 20QA-2 not opening in DC pump operation.
why this SOV given?
can't we bypass this?
Is this really a GE Frame 5 with an Off Base L.O. skid? First I've ever seen. Can you upload some Flow Diags. to somewhere?
> Is this really a GE Frame 5 with an Off Base L.O. skid?
> First I've ever seen. Can you upload some Flow Diags. to somewhere?
although we found problem in logic. while running DC EOP, SOV closed. as per present logic. so need to force. but yet to know why SOV is given?
Looks like the solenoid is controlling the return to tank flow back to the tank depending on the return line pressure. Can you show the logic for the operation of the solenoid.
Have you talked to BHEL about this?
SOV is Close/open type.
Logic given in box while machine running and only AC pump running
Logic box 155,180,190
- 63QA4A AC pump discharge Pr switch
- 63QA4B LO header Pr switch
- 52QA2 AC run feed back
- 4QEZ2 DC start Logic (wrongly given 1 while DC pump stooped become 0 when DC pump starts)
- final output 20QA2 is SOV open command
when AC pump fail Logic box 180 Beng's all Three input A (AC motor not running), B (when DC start its state changes to 0), Not Of C (AC pump discharge Pr switch operated) becomes Zero so SOV closed.
Can't we make it simple? means why we used fuel pump which need extra LO circuit network.if it require at all why not same LO which is used by GT bearings?
i worked on Hitachi H25 Machine machine its Fuel pump does not required LO at all.
what is today's Development in Frame V machine of GE.(As in earlier Post you question ? (Is this really a GE Frame 5 with an Off Base L.O. skid? First I've ever seen)
can we make such arrangement by replacing warren make pump which does not require extra LO circuit?
All GE-design Frame 5 machines, and their look-alikes, are not identical. Many GE-design Frame 5 heavy duty gas turbines were packaged by many different companies over several decades, and the auxiliaries were quite often different--but provided the required functionality to control and protect the turbine and auxiliaries.
There must be some reason we are not aware of for the off-base skid to provide L.O. for the on-base liquid fuel pump. Is the oil in the off-base skid some kind of special oil, different from the L.O. used for bearings and hydraulic system? Is it possible that if the Warren pump developed a leak that the liquid fuel (distillate? naphtha? ???) could contaminate the main, on-base lube oil reservoir?
You would likely need to talk to BHEL or a pump manufacturer/vendor to source a pump which could be used which didn't require the unique lubrication.
It does seem there is some issue with the logic you provided. How often does the unit operate on liquid fuel?
Isn't one of the "main" problems that 88QA-2 is stopping? Why is 88QA-2 stopping, which would require 88QE-2 to operate?
How new is the unit? Is it still under warranty from the supplier/packager?
Again, it does appear there is some kind of issue with the sequencing, and while it may definitely be possible to change the liquid fuel pump we don't have enough information about the unit to be able to make any recommendations to that effort--and, indeed, while that may be an option it may not be the right option for the long-term or for the circumstances (which we do not have any information).
Myself, I would be doing three things. First, investigating and resolving the issue with 88QA-2 stopping. Second, review the I/O and the sequencing to make sure it's correct. It's not all that unusual for there to be an incorrect sense contact used in sequencing and for that not to be discovered during commissioning (especially for a unique situation, such as an off-base L.O. skid for a unique liquid fuel pump lubrication requirement)--it's unfortunate, but it's not all that unusual. BUT, I would definitely be working with BHEL on this particular issue because they may be aware of other requirements/issues you, and we, are not--given there is this unique off-base L.O. skid. They may even be able to tell you why--and if--20QA-2 is required. (I suspect it has something to do with trying to keep the L.O. lines filled with oil when the unit is not running on liquid fuel--but that's just a great big SWAG (Scientific Wild-Arsed Guess) on my part.
Finally, third, if you feel the running reliability of the unit definitely is adversely affected by the use of a liquid fuel pump which requires it's own lubrication system, you should be working with either BHEL or a pump manufacturer/manufacturer's representative to determine if there is a suitable pump for your application that does not require a separate L.O. supply. We have no idea how long the unit has been running before this problem became apparent (which it appears to have become apparent when the stopping of 88QA-2 started....). So, is it really a running reliability problem once the problem of 88QA-2 is resolved and the application code (logic) problem is understood and resolved? If it's been running for some time with no problems--until 88QA-2 started stopping, then, restore 88QA-2 reliability, and if it's determined there is a problem with the 20QA-2 control then fix that problem--and the prior running reliability will be restored.
Hope this helps!
Thanks CSA & Mr. Glenmorangie for your reply
>How often does the unit operate on liquid fuel?
it always running on Naphtha.
>Isn't one of the "main" problems that 88QA-2 is stopping?
>Why is 88QA-2 stopping, which would require 88QE-2 to operate?
Yes problem is with 88QA-2 Motor bearing seize.SO 88QE-2 Started in Auto.
>How new is the unit? Is it still under warranty from the supplier/packager?
commissioned in 2013. we used Servo system 150(IOCL) LO for this skid. This is the second time Problem arises in the history of machine when 88QA-2 fail 88QE-2 comes in line but on DC LO temp raise to trip level. earlier we couldn't concluded the problem of SOV and thought DC pump is only for safe shut down. but this time we can figure out with the help of SOE and found problem in Logic.
but its very difficult to work on AC pump for maintenance purpose due to poor design. As we r having only one source (this GT) so reliability of this machine is at most priority so we are under planning to purchase another parallel skid.
parallel i will contact warren pump manufacture for suggestion of fuel pump without this skid.
CSA please informed me the out come of discussion with BHEL.
& Mr Glenmorangie my unit is in Bongaigaon Dist of State of Assam (India)
Thank you for your answers.
I didn't mean to imply that I was going to be contacting BHEL about this issue. I was just stating that if the problem were at my site I would be taking the three actions I mentioned.
Certainly, BHEL, as the "designer" of this skid, would be the best people to consult with regarding reliability issues and serviceability issues. If they are considering selling more units with similar off-base skids and liquid fuel pumps, they would be most interested in the feedback from Customers who are using this scheme to try to improve the equipment and its reliability.
You can also talk to the manufacturer of the 88QA-2 pump motor to see if the proper motor was selected to power the pump. Some motors are designed to be operated vertically, and others designed to be operated horizontally. There are actually MANY considerations in the choice of an electric motor for a particular application/service. There may be a better choice--and it might come from the same motor manufacturer, or it might come from a different manufacturer. You can consult with different electric motor manufacturers' representatives in your area to get their recommendations.
You might also talk to a bearing manufacturer to see if there's a more durable alternative for this particular application.
Have you considered the possiblity of adding a second AC motor-drive pump to the existing off-base skid? Running for long periods of time on a DC motor is not usually a good choice.
Again, one has to believe that the packager (BHEL) had a specific reason for this pump lubrication scheme.
Does the unit start and stop on naphtha? Or does it use distillate fuel ("high-speed diesel"; #2 diesel; etc.) for normal starting and stopping?
You also mentioned cooling. What's the issue with cooling? Is it that 20QA-2 isn't allowing L.O. flow when the DC pump is running and then the oil temperature in the liquid fuel pump gets too high?
Again, it certainly seems there is a problem with the logic for 20QA-2. But, again, it would be best to consult with BHEL on this because they might have information that would be helpful. For, example, would it be possible to use some kind of spring-operated check valve in place of the solenoid valve that had a cracking (opening) pressure that would maintain oil in the system when not running? (Here, again, I'm guessing that's the purpose of 20QA-2--only BHEL would be able to say for sure!). The liquid fuel check valves on the turbine are usually rated to open only when the liquid fuel pressure gets above approximately 100 psig; and check valves can be ordered with lots of different cracking (opening) pressures, and flow-rates, and for different fluids. Perhaps this would negate any need for a solenoid-operated valve.
But, that's not going to solve the issue with the reliability of 88QA-2--which is your main problem (in my personal opinion) at this point. Certainly, understanding the purpose of 20QA-2 (which can probably only be answered by BHEL), and then correcting, if necessary, the logic to keep 20QA-2 open when the DC pump is running (IF the DC pump is intended to remain running while the AC pump is being repaired--again, something only BHEL can likely answer) will help somewhat. But, if access and maintenance issues make it difficult to repair or replace 88QA-2, then those problems should also be solved. And, perhaps an 88QA-3 might be possible.
Please write back to let us know how you fare in resolving this (these) issues!
Have you looked in the unit Operations & Service Manuals, in the Liquid Fuel section, to see if there's any information there about the off-base L.O. skid for the liquid fuel pump? And, possibly what the purpose of 20QA-2 is?
Also, could it be that one possible reason for the off-base L.O. skid could be cooling for the liquid fuel pump? I know that at some sites the naphtha is very warm. I think you mentioned something about the unit tripping on high L.O. temperature. But, there is a pressure transmitter and TWO (2) pressure switches downstream of 20QA-2. Did the Mark VIe not annunciate at least one alarm that the piquid fuel pump L.O. pressure was low (downstream of 20QA-2) when 88QA-2 stopped???
I also note that on the P&ID you provided, there is no setting for VTR3-1.... What temperature is that "thermostat" set for?
Again, BHEL would likely be the best source of information--if there's nothing in the Operations & Service Manuals that's of any help.
And, do please write back to let us know how you fare in resolving this issue. A LOT of customers do end up replacing some components or re-engineering systems--but, as you asked in your original post--it's usually AFTER they fully understand the system and how it's supposed to operate. Hopefully we have been able to help understand some possible operational considerations, and hopefully you can work with BHEL to fully understand the system, and in the process make the necessary changes to achieve the desired system reliability.