the gas turbine was on cranking modeWas there any jobs on those pumps logic command ?
thank you very much, first of all the main lube oil motor is shaft driven like you said. i dont think i said it is electric motor. my question was "the auxilliary lube oil motor (88QA) comes on at low lube oil pressure from the pressure switch 63QA even when the pressure from main lube oil discharge header was shown okay on the guage. At about 95% turbine reaches a self sustaining speed and the auxilliary lube oil pump will stop and the shaft driven main lube oil pump continue throughout the operations except there is a drop in pressure from the main lube oil pressure header. now in this case at full speed no load, the low lube oil alarm comes on and call in auxilliary lube oil pump to start up where is the pressure from the guage is ok. the switch was calibrated and found ok, the oil level is ok, so what could bring up the low lube oil alarm? the turbine is GE frame 6, mechanical drive.ekongmark,
Please tell us what kind of gas turbine you are experiencing this problem with: Manufacturer; size; application (generator drive or mechanical drive).
I can guess that it's a GE-design heavy duty gas turbine, because of the device number (88QA), but I have never personally seen one with a "main lube oil motor" and an Auxiliary L.O. Pump motor. Many GE-design heavy duty gas turbines have an Accessory Gear-drive Main L.O. Pump--not a motor-driven Main L.O. Pump. When the machine is spinning (either during CRANKing, or Acceleration or coasting down to zero speed) the Accessory Gear is spinning and driving the Main L.O. Pump. At low speeds (less than approximately 100 RPM of turbine shaft speed) the output of the Main L.O. Pump is usually below rated pressure and flow, but as turbine shaft speed increases the pressure and flow of the Main L.O. Pump increases.
When the turbine is "running" (my definition of "running" means anything above zero speed for GE-design heavy duty gas turbines) the
The Auxiliary L.O. Pump SHOULD be running during CRANKing, and acceleration to near rated turbine shaft speed and during deceleration from rated turbine shaft speed to zero speed. That ensures that there is sufficient pressure AND flow to the bearings of the turbine and axial compressor and the reduction gear (if so equipped) and the driven device (a generator, for example). When the machine is running at rated turbine shaft speed, the Auxiliary L.O. Pump should ONLY run when the output pressure of the Accessory Gear-driven Main L.O. Pump is not sufficient to provide flow to the bearings. There is a pressure switch (and maybe a pressure transmitter) monitoring the bearing L.O. pressure and if it drops below a certain pressure setpoint then the Aux. L.O. Pump will start to protect the bearings.
SOOOO, if the unit is CRANKing, unless there's something we don't know about the machine and its configuration/operation 88QA SHOULD BE running even if the Main L.O. Pump is spinning and producing output flow and pressure. It would be unusual if the Aux. L.O. Pump was not running during CRANKing, acceleration and deceleration.
The concept of having an Accessory Gear-driven (the Accessory Gear is driven by the turbine shaft) Main L.O. Pump (AND the Main Hydraulic Pump) is that when the unit is running at rated turbine shaft speed the power for the pump(s) is being provided from the turbine shaft--NOT from an electric motor-driven pump (or pumps). This provides a high degree of reliability for the equipment when it is running. (Newer GE heavy duty gas turbine designs have gotten completely away from this decades-old and proven design, using two, redundant AC motor-driven L.O. pumps--one operated in Standby (LAG) mode. Just a different design philosophy is all; things do change over time, after all. Some things, anyway.) The Auxiliary AC motor-driven pump(s) are primarily there to provide flow/pressure in the event of a failure of the Main (Accessory Gear-driven) pump(s). (Some older GE-design heavy duty gas turbines did not have an AC motor-driven Aux. Hydraulic Pump.) These pumps are also used to provide flow and pressure during starting and deceleration to ensure there is always sufficient flow to the bearings, in addition to providing back-up in the event of a Main pump failure.
We're not there alongside you at your site, so we don't know what you see or what you know. BUT, it seems you don't understand the GE-design heavy duty gas turbine operation/controls philosopy as explained above. I hope this helps. If you need further clarification, you are going to have to provide the requested information.
oh yeah! lol, that was a typo error (the main lube oil motor stuff) as you can also see the subsequent tread says otherwise ( 88QA KEEP COMING ON WHEN THE TURBINE MAIN LUBE OIL PUMP IS RUNNING). however, thanks so much for the corrections i really appreciate. yes the mechanically actually did'nt do all the valve alignment or someone mistakenly closes a valve that was suppose to be open along the mist line, currently that issue was taken care of. for the 66QA issue, we will look at these recommendations you gave here though we tracing it also to valves in the sump (VR1). will keep you abreast with development concerning the issue. I really appreciate. Facts i did'nt tell you: I'm new in the system (less than a yeah 8 months approximately), working in I&C UNIT. will really appreciate if you have materials that can also help my growth in control. thank youEr, …, Uh, …, Um, here’s exactly what you wrote in your original post:
“Good morning everyone, please our auxilliary lube oil pump keep coming on when the main lube oil motor is running, …” (The emphasis (bold font) is added by me.)
You added in a subsequent response to your original post:
“the gas turbine was on cranking mode”
In your most recent reply you wrote:
“my question was "the auxilliary lube oil motor (88QA) comes on at low lube oil pressure from the pressure switch 63QA even when the pressure from main lube oil discharge header was shown okay on the guage….” And:
"now in this case at full speed no load, the low lube oil alarm comes on and call in auxilliary lube oil pump to start up where is the pressure from the guage is ok." And:
“the switch was calibrated and found ok, the oil level is ok, so what could bring up the low lube oil [pressure] alarm?”
I’m not a fan of revisionist writing/history. Your original post is MUCH different from what you're saying you wrote.
A shaft-driven pump is not a motor-driven pump.
Obviously, there’s either a problem with the 63QA switch, or the wiring, or that particular contact input channel to the turbine control system, or the valves of the pressure switch are not in the proper positions, or the line that provides the pressure to the switch is plugged—or something like the above. Have you put a known-to-working-and-calibrated pressure gage on the pressure line to the switch to see what it indicates? Have you tried toggling the contact input signal from the switch to the turbine control system to see what happens to the indication? Have you measured the voltage of the two wires connected to the 63QA pressure switch to verify the correct voltages are there?
You also mentioned a problem with the L.O. Mist Eliminator or Bearing Evacuator system. That should not be occurring when the Aux L.O. Pump is running, so that’s probably a separate issue which makes wonder: When did this problem start? After a maintenance outage? Is it possible that something was not assembled correctly? I know--the Mechanical Department says everything is perfect and that the problem is the turbine control system. Prove them wrong by systematically and logically eliminating every possible cause of this problem other than improper reassembly.
And the same for the 63QA pressure switch problem. You don't seem to have properly sorted out the switch, it's sensing lines/valves, and/or the contact input circuit/channel/wiring as possible causes.
This is apt, I really appreciate. I'm happy to be in this forum. Thanks so muchEverybody has to start somewhere. I try VERY HARD to remember what it was like when I started and how I wouldn't be here today if not for the grace and support of people I'd never met but came to know and call friends.
As for materials--there is a HUGE amount of Speedtronic Mark*-related information here on Control.com--more than 20 years of threads. Many are WELL OUTSIDE the realm of controls--BUT, we all have to remember that a control system uses, and relies upon, many mechanical devices that are not directly controlled by the control system. It's all related--though sometimes people (usually the Mechanical Department!) want to blame the control system for EVERYTHING! First, because the mechanical team rarely, if ever, makes a mistake of any kind (just ask them--they will tell you!). Second, that control system has SO MANY wires and LEDs and it just has to be the cause of just about every problem. And, if it's not the control system, then it's the inputs to the control system (Thermocouples; RTDs; pressure transmitters; speed pick-ups; vibration sensor; flame detectors; and on and on and on). They can NEVER believe that the sensors are working correctly and that the control system can accurately detect mechanical problems it just doesn't (YET) have the smarts (machine learning; AI (Artificial Intelligence); fuzzy logic) to specifically say, "Go and check that manual valve downstream of the lube oil mist eliminator." It doesn't know that oil is puking out of the discharge of the mist eliminator--yet.
Why? Because there are companies and individuals who fervently believe control systems are currently at the stage where power plants and similar installations can be run reliably and safely without humans being on site. That's a brave and ambitious way of thinking, and I suppose that many technological advances would never occur without that kind of thinking.
So, what I recommend you do is get your own copies of the P&IDs for all the turbine and auxiliary systems and study them. Make notes on them. Go out to the equipment and find every device--know where the devices are located. And work closely with the operators and mechanical department to learn about sequences and processes and devices and equipment that you don't already know about. Use every resource you can find--beginning with the P&IDs and the Operations & Service Manuals provided with the equipment. Control.com is a very good resource--why? Because more than many other forums people usually provide feedback (we encourage them to) so others reading the posts now and in the future can know what worked and what didn't work when trying to solve the same or a similar problem.
If you need clarification on a past post--you can add to that post and ask for clarification. If you haven't found any information related to what you need help with, open a new thread/post. And, most of all, remember to provide feedback. Feedback is the most important contribution here at Control.com.
A few years back there was a very long thread about how to read/interpret relay ladder logic as implemented in Mark* control system. That is a very good thread. Reading logic/sequencing/programming/application code is almost like learning a new language, only it's simpler (in my personal opinion). You seem to be learning that device numbers are important--learn all of the device numbers GE uses and commit them to memory. There are other threads about Mark* signal names and how to interpret them--also, very important.
As you become familiar with GE naming and controls philosophies you must remember that, until GE Belfort was (mistakenly) given autonomy for turbine control philosophy for a large group of GE-design machines GE was AMAZING at just writing and implementing some very ingenious sequencing/logic which worked well for DECADES--and continues to work well in thousands of GE machines around the world. As GE machines grew larger they worked VERY hard to keep the same controls philosophies so that the machines were similar to smaller units. So, what you learn on this machine will be very similar to many other GE-design machines.
And, if you are young and want to work on more advanced control systems knowing processes and sequences will help you immensely as you progress in your career.
Now, about VR1. That stands for Valve-Relief Number 1. The Accessory Gear-driven Main L.O. Pump is a positive displacement pump. VR1 is used to control the output pressure of the Main L.O. Pump--it's NOT NORMAL to use a relief valve to control pressure, but in this case it works very well and has been used for more than six (6) decades as the means for controlling Main L.O. Pump discharge pressure on GE-design heavy duty gas turbines with shaft-driven Accessory Gear boxes. I have only ever seen one VR1 failure, and that was because of a failure of the Main L.O. Pump (the gear teeth sheared off), and I've only ever seen that one Main L.O. Pump failure. I have seen the coupling between the Accessory Gear drive and the Main L.O. Pump break twice--but other than I have seen machines that were more than 50 years old still running with the same Main L.O. Pump they were supplied with. And, I have 40+ years of experience working on GE-design heavy duty gas turbines. I don't even know if VR1 has an adjusting mechanism....
Here's a test you can run. While the unit is accelerating during a START above, say, 60% speed, have someone go to the Aux. L.O. Pump motor starter and move the HOA (Hand-Off-Auto) switch to OFF and hold it there while someone else is monitoring the Main L.O. Pump discharge pressure. If the L.O. pressure doesn't drop, then VR1 is doing its job and the Main L.O. Pump has some kind of issue. These two people--and the control room operator--need to be in communication with each other ("walkie-talkies") and if the bearing header pressure drops below 1.35 bar (about 20 psi or so) the person holding the Aux. L.O. Pump HOA switch in the OFF position needs to let go of the switch and let it go back to the AUTO position and the Aux. L.O. Pump will start and run. If the Bearing Header pressure drops quickly when the Aux. L.O. Pump is stopped, let go of the HOA switch or the unit might trip (and if it does it's not at rated speed or under load--this is just a test) and the Emergency L.O. Pump will supply pressure to the bearings.
It's important to remember that running the turbine with a failed or failing Main L.O. Pump--running at rated speed and with a load on the turbine--means that if the Aux. L.O. Pump fails or the Aux. L.O. Pump motor fails, or the plant experiences a loss of AC power (to run the Aux. L.O. Pump) the Main L.O. Pump can't help supply oil to the bearings! You will be relying entirely on the Emergency L.O. Pump AND the battery that powers the Emer. L.O. Pump to keep oil flowing to the bearing as the unit coasts down to zero speed.
Good luck in your career!
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