IGNITION SPEED OF 5Frame GT

Hi Everyone,
We have GE MS5002E at our plant, we are going to do first fire, cranck, cooldown and etc. The our subcontractor provided for approving the the instruction of commissioning procedure where it pointed that ignition speed is about 5200 rpm. I am sure that it is false, because when I have read this instruction I have seen L14HM(ignition speed) is about 16 percent of nominal speed. I think that this speed is about 1300 rpm. Is there anybody who can help me with this information and give me advice.
 
ControlEng99,

L14HM is "minimum" firing speed, meaning that ignition should not take place below TNK14HM1 (you noted the value was 16%, so 16% of a nominal 5100 RPM (the typical rated axial compressor speed for GE-design Frame 5 heavy duty gas turbines (the actual rated speed for a particular unit is dependent on several factors, most importantly the Load (Reduction) Gear rating)) is 816 RPM. In actuality, the speed at which the ignitors are energized and fuel is admitted is usually approximately 18-22% of rated speed, sometimes a little higher or lower, depending on the torque converter configuration--so say somewhere around 918 RPM to 1122 RPM, give or take a few RPM. Again this depends on a lot of factors (especially when the unit is new and bearings are tight and axial compressor clearances are tight and the torque converter is new and the starting motor (either an electric induction motor, or a diesel engine which may have some "newness" issues as well). But you can count on a speed of about 20% or so, so 1/5th of rated speed (which comes from the Load Gear nameplate!), which is usually around 5100 RPM, give or take a few RPM as was noted above.

Firing CANNOT occur at 5200 RPM--there's just TOO MUCH air flowing through the machine and combustors at that speed for flame to be reliably established and for the exhaust temperature (and internal combustor temperatures) to be reasonable. That was a typographical error.

I would suggest the order should be to put the unit on COOLDOWN for a couple of hours, maybe even four hours or so. People should be stationed in various compartments listening for any unsual noises as the shaft is rotated while on COOLDOWN. The purpose of this test is to let COOLDOWN try to remove any bow or sag in the turbine/compressor rotor which naturally occurs when the unit has not been rotated for a long time.

Next, a bump check should be performed (a test where several people are listening for rubs and unusual noises in various compartments (Accessory Compartment; Turbine Compartment; Load Compartment; Generator Collector Compartment) after a unit START is initiated, and the unit is tripped (using the big red Emergency Stop Push-button) very shortly after the shaft begins to rotate. This allows those listening in the compartments to hear any unusual noises or rubs (where components are rubbing against each other that should not be rubbing against each other) as the unit begins to turn. The purpose of using the big red pushbutton is to test the emergency stopping capability of the unit during a START before flame is established--a good thing to test. And, to let the unit return to zero speed, and possibly go on COOLDOWN automatically (some units do go on COOLDOWN automatically any time they are above zero speed; others only if flame was established before a trip or STOP is initiated). NOW, be aware that there will likely be some "bumping" heard in the Load Compartment--that's normal. It's because of the difference in inertias of the turbine/compressor rotor and the generator rotor AND the backlash which is built into the load gear teeth. It can sound pretty bad--but it's really to be expected.

If this test is successful (meaning the unit stops and returns to zero speed/COOLDOWN and no horrific rubs or other noises are noted), the the next step would be to select CRANK and initiate a START and let the unit go through a normal acceleration to CRANK speed for a few minutes (doesn't hurt anything to do this), and then a normal STOP should be initiated from the HMI. The same people should be stationed in the same compartments listening for the same unusual noises as the unit coasts down (which can take several minutes sometimes, or if the clearances are all tight (as they are usually on a new machine, it might only take a couple of minutes). The unit may automatically go on COOLDOWN (depending on how the turbine control system is programmed).

After these tests are successfully performed, then AUTO can be selected and the unit can be STARTed. (I prefer to select FIRE mode, and after flame is established the turbine compartment and fuel valves are checked for leaks. If all is good, then AUTO is selected and the unit will accelerate to rated speed (FSNL, Full Speed-No Load).

It should be noted that if people are stationed in compartments that are protected by fire extinguishing agents such as CO2 or other dangerous-to-humans agents, that fire protection should be temporarily disabled for the bump check and the first CRANK tests--but should be in service for the first fire test. And people should be aware of the fire indications and prepared to close compartment doors if the fire alarm sounds (VERY IMPORTANT to close doors!!!) and get quickly away from the compartments.

Best of luck--please write back to let us know how you initial operational checks go!
 
ControlEng99,

L14HM is "minimum" firing speed, meaning that ignition should not take place below TNK14HM1 (you noted the value was 16%, so 16% of a nominal 5100 RPM (the typical rated axial compressor speed for GE-design Frame 5 heavy duty gas turbines (the actual rated speed for a particular unit is dependent on several factors, most importantly the Load (Reduction) Gear rating)) is 816 RPM. In actuality, the speed at which the ignitors are energized and fuel is admitted is usually approximately 18-22% of rated speed, sometimes a little higher or lower, depending on the torque converter configuration--so say somewhere around 918 RPM to 1122 RPM, give or take a few RPM. Again this depends on a lot of factors (especially when the unit is new and bearings are tight and axial compressor clearances are tight and the torque converter is new and the starting motor (either an electric induction motor, or a diesel engine which may have some "newness" issues as well). But you can count on a speed of about 20% or so, so 1/5th of rated speed (which comes from the Load Gear nameplate!), which is usually around 5100 RPM, give or take a few RPM as was noted above.

Firing CANNOT occur at 5200 RPM--there's just TOO MUCH air flowing through the machine and combustors at that speed for flame to be reliably established and for the exhaust temperature (and internal combustor temperatures) to be reasonable. That was a typographical error.

I would suggest the order should be to put the unit on COOLDOWN for a couple of hours, maybe even four hours or so. People should be stationed in various compartments listening for any unsual noises as the shaft is rotated while on COOLDOWN. The purpose of this test is to let COOLDOWN try to remove any bow or sag in the turbine/compressor rotor which naturally occurs when the unit has not been rotated for a long time.

Next, a bump check should be performed (a test where several people are listening for rubs and unusual noises in various compartments (Accessory Compartment; Turbine Compartment; Load Compartment; Generator Collector Compartment) after a unit START is initiated, and the unit is tripped (using the big red Emergency Stop Push-button) very shortly after the shaft begins to rotate. This allows those listening in the compartments to hear any unusual noises or rubs (where components are rubbing against each other that should not be rubbing against each other) as the unit begins to turn. The purpose of using the big red pushbutton is to test the emergency stopping capability of the unit during a START before flame is established--a good thing to test. And, to let the unit return to zero speed, and possibly go on COOLDOWN automatically (some units do go on COOLDOWN automatically any time they are above zero speed; others only if flame was established before a trip or STOP is initiated). NOW, be aware that there will likely be some "bumping" heard in the Load Compartment--that's normal. It's because of the difference in inertias of the turbine/compressor rotor and the generator rotor AND the backlash which is built into the load gear teeth. It can sound pretty bad--but it's really to be expected.

If this test is successful (meaning the unit stops and returns to zero speed/COOLDOWN and no horrific rubs or other noises are noted), the the next step would be to select CRANK and initiate a START and let the unit go through a normal acceleration to CRANK speed for a few minutes (doesn't hurt anything to do this), and then a normal STOP should be initiated from the HMI. The same people should be stationed in the same compartments listening for the same unusual noises as the unit coasts down (which can take several minutes sometimes, or if the clearances are all tight (as they are usually on a new machine, it might only take a couple of minutes). The unit may automatically go on COOLDOWN (depending on how the turbine control system is programmed).

After these tests are successfully performed, then AUTO can be selected and the unit can be STARTed. (I prefer to select FIRE mode, and after flame is established the turbine compartment and fuel valves are checked for leaks. If all is good, then AUTO is selected and the unit will accelerate to rated speed (FSNL, Full Speed-No Load).

It should be noted that if people are stationed in compartments that are protected by fire extinguishing agents such as CO2 or other dangerous-to-humans agents, that fire protection should be temporarily disabled for the bump check and the first CRANK tests--but should be in service for the first fire test. And people should be aware of the fire indications and prepared to close compartment doors if the fire alarm sounds (VERY IMPORTANT to close doors!!!) and get quickly away from the compartments.

Best of luck--please write back to let us know how you initial operational checks go!
Thank you CSA for your full reply and even more, I agree with you that it is typographical fail, and the most awful thing that we have to check their documentation and instructions or program. Currently We have finished to fill the oil tank it is about 16 tons, and 90 percent field devices are installed, and now is starting the most interesting thing like energize DCS and start doing loop checks procedure and preparing unit for all steps which you described. Thank you a lot, Sometimes it seems to me that there is no question for you the answer of which you don't know.
Best wishes
 
ControlEng99,

Documentation and procedures. It is very rare to find either which is well-written these days. When engineers write documentation or procedures they concentrate on all the things which WERE NOT obvious to them, thinking that everything that WAS obvious to them WILL BE obvious to everyone else, too--and so they generally only write about the things that weren't so obvious to them or that caused them trouble or issues.

Worse, even, is the fact that a LOT of documentation and procedures are assigned to junior engineers or interns or trainees--as if they have the experience necessary to write good documentation and procedures when they themselves haven't probably much if any experience with the equipment. So, they are left to comb through other documentation and procedures to produce their deliverable.

Worse, STILL, is that the work product (documentation and procedures) is rarely, if at all, proof-read for accuracy or completeness. People just don't like to read documentation, and when they read procedures they only concentrate on the items they deem necessary or important (regardless of their experience). (For proof positive, read the LVDT calibration procedures in the GE Control Specification--they are horribly written, incomplete, and still people don't follow all the steps listed.)

Anyway, typographical errors do occur--they are a fact of life. And, when procedures have to be produced for commissioning activities they are usually hastily written and rarely proof-read before being handed to the Customer as final and complete (with a few corrections necessary :)). And, again, usually lesser-experienced people are assigned the (onerous) task of writing them (as if this will make them better writers in the future--it ONLY means they will endeavour to ensure they never have to write procedures again, and because it was assigned to them when they were newbies it's okay to assign it to other newbies later in their careers).

Commissioning is usually a very difficult task--it doesn't need to be, but it is because construction is usually always late delivering their work product. Think about commissioning--it primarily involves testing wiring and circuits and field devices and instruments (often called "loop-checking") and then performing functional checks of safety equipment and the overall plant. Quite often commissioning is started before field devices and instruments are all installed, and most often before even 90% of the wiring and terminations are complete. I have been forced to begin commissioning without batteries to power the turbine control system being installed, and without network cabling and power supplies for the HMIs. This is 100% true--and it has happened on more than several occasions. Why? Because construction is late, and project management is inept and can't get construction to develop, implement and adhere to a recovery plan to get the job back on schedule. And, because the commissioning personnel were brought to site because a schedule said commissioning will begin on a certain day (even though on that certain day many construction activities were incomplete) and so the commissioning people arrive only to have to wait, and wait, and wait. And project management--and the Customer--don't like to see commissioning people sitting and waiting. And, the project end date never get changed to reflect the lateness of construction. Project management will just "squeeze" commissioning, forcing them to work very long days, weeks in a row without a day off, and even double-shift (24 hours a day)--which is THE MOST UNPRODUCTIVE mode for commissioning (unless there are good commissioning personnel who have worked together in the past and have good leadership and can communicate what they need to have finished when in order to be as productive as possible)).

For me, commissioning is a very gratifying job--and it can be very satisfying and rewarding. But, that's if project management is realistic and will gather together all the disciplines and help prioritize work activities so that commissioning can proceed in something of an orderly fashion. I have been told MANY times that commissioning is the critical path activity and that it is expected that commissioning will be the cause of missing the project completion date. And, I have been sitting and waiting for mechanical completion MANY times, having worked with construction to get wiring and terminations complete, and devices loop-checked, and L.O. loaded and hydraulics up and running and functional checks complete. And, when it is announced in the morning project meeting that commissioning could start the unit today if compartment enclosures were finished and fire protection system integrity was complete and cooling water was available and fuel was available that the unit could be started today--well, you can imagine what happens. Commissioning personnel are told they can leave the meeting, and the screaming begins before the meeting room door is closed. Things really start happening--and fast. Construction and mechanical completion have become the critical path, and a fire is built under them to get finished. Soon.

That's the really fun part--seeing people who have been skating along missing all kinds of milestones and deadlines with the belief that commissioning will be made out to be the villains when the project is late--only to find they have become critical path! I like loop-checking, too--it's easy and simple when it's done in a logical and methodical fashion. It's possible (and has been done many times) to complete more than 150 loops (circuits/field devices/instruments) in a single 10-hour day with two people! (On many sites, it's rare to get 20 loops done in a single day, with four or five commissioning personnel--especially if very often the crew starts to check a field device or instrument only to find the field device or instrument hasn't been installed, or the wire and cable hasn't been pulled or terminated, or it's only terminated at one end. So, they have to switch to another loop, often to find a similar situation.)

So, you are good to question--I call it thinking critically. It's good that someone is reading the procedures and finding problems before they become show-stoppers. It makes the procedures that much more usable and credible and reliable, than finding issues when you're trying to actually perform them and regularly finding problems and mistakes. And a word of caution, kindly pointing out mistakes you find will be much more well-received.... That's from painful, personal experience. Remember--most procedures were hastily written, by people who probably don't have that much experience with the equipment. (It's supposed to make them better engineers, remember?) And, there are occasional typographical mistakes, too!

Best of luck! Enjoy. One of the single most important things to be learned during commissioning is: The location of field devices and instruments. The OTHER really important thing to learn is: Valve positioning. There are LOTS of manual valves in plants and they all have to be in a certain position for the plant to start and run reliably. People need to know where these valves are, and what positions they need to be in. Learn to read--AND USE--the P&IDs (Piping & Instrumentation Diagrams)!!! And, where each of the devices on the P&IDs are located. Sitting in front of an HMI isn't where you're going to learn either of the above. And, if you're going to be an operator or technician at the plant, you will have PLENTY of time to sit in front of an HMI. You need to be outside, crawling over the equipment, finding and testing devices ("loop-checking") and learning to use the P&IDs. You need to hear and feel and see equipment working and starting. And that DOES NOT happen sitting in front of an HMI during commissioning.

And, thanks, by the way for the kind words.
 
ControlEng99,

Documentation and procedures. It is very rare to find either which is well-written these days. When engineers write documentation or procedures they concentrate on all the things which WERE NOT obvious to them, thinking that everything that WAS obvious to them WILL BE obvious to everyone else, too--and so they generally only write about the things that weren't so obvious to them or that caused them trouble or issues.

Worse, even, is the fact that a LOT of documentation and procedures are assigned to junior engineers or interns or trainees--as if they have the experience necessary to write good documentation and procedures when they themselves haven't probably much if any experience with the equipment. So, they are left to comb through other documentation and procedures to produce their deliverable.

Worse, STILL, is that the work product (documentation and procedures) is rarely, if at all, proof-read for accuracy or completeness. People just don't like to read documentation, and when they read procedures they only concentrate on the items they deem necessary or important (regardless of their experience). (For proof positive, read the LVDT calibration procedures in the GE Control Specification--they are horribly written, incomplete, and still people don't follow all the steps listed.)

Anyway, typographical errors do occur--they are a fact of life. And, when procedures have to be produced for commissioning activities they are usually hastily written and rarely proof-read before being handed to the Customer as final and complete (with a few corrections necessary :)). And, again, usually lesser-experienced people are assigned the (onerous) task of writing them (as if this will make them better writers in the future--it ONLY means they will endeavour to ensure they never have to write procedures again, and because it was assigned to them when they were newbies it's okay to assign it to other newbies later in their careers).

Commissioning is usually a very difficult task--it doesn't need to be, but it is because construction is usually always late delivering their work product. Think about commissioning--it primarily involves testing wiring and circuits and field devices and instruments (often called "loop-checking") and then performing functional checks of safety equipment and the overall plant. Quite often commissioning is started before field devices and instruments are all installed, and most often before even 90% of the wiring and terminations are complete. I have been forced to begin commissioning without batteries to power the turbine control system being installed, and without network cabling and power supplies for the HMIs. This is 100% true--and it has happened on more than several occasions. Why? Because construction is late, and project management is inept and can't get construction to develop, implement and adhere to a recovery plan to get the job back on schedule. And, because the commissioning personnel were brought to site because a schedule said commissioning will begin on a certain day (even though on that certain day many construction activities were incomplete) and so the commissioning people arrive only to have to wait, and wait, and wait. And project management--and the Customer--don't like to see commissioning people sitting and waiting. And, the project end date never get changed to reflect the lateness of construction. Project management will just "squeeze" commissioning, forcing them to work very long days, weeks in a row without a day off, and even double-shift (24 hours a day)--which is THE MOST UNPRODUCTIVE mode for commissioning (unless there are good commissioning personnel who have worked together in the past and have good leadership and can communicate what they need to have finished when in order to be as productive as possible)).

For me, commissioning is a very gratifying job--and it can be very satisfying and rewarding. But, that's if project management is realistic and will gather together all the disciplines and help prioritize work activities so that commissioning can proceed in something of an orderly fashion. I have been told MANY times that commissioning is the critical path activity and that it is expected that commissioning will be the cause of missing the project completion date. And, I have been sitting and waiting for mechanical completion MANY times, having worked with construction to get wiring and terminations complete, and devices loop-checked, and L.O. loaded and hydraulics up and running and functional checks complete. And, when it is announced in the morning project meeting that commissioning could start the unit today if compartment enclosures were finished and fire protection system integrity was complete and cooling water was available and fuel was available that the unit could be started today--well, you can imagine what happens. Commissioning personnel are told they can leave the meeting, and the screaming begins before the meeting room door is closed. Things really start happening--and fast. Construction and mechanical completion have become the critical path, and a fire is built under them to get finished. Soon.

That's the really fun part--seeing people who have been skating along missing all kinds of milestones and deadlines with the belief that commissioning will be made out to be the villains when the project is late--only to find they have become critical path! I like loop-checking, too--it's easy and simple when it's done in a logical and methodical fashion. It's possible (and has been done many times) to complete more than 150 loops (circuits/field devices/instruments) in a single 10-hour day with two people! (On many sites, it's rare to get 20 loops done in a single day, with four or five commissioning personnel--especially if very often the crew starts to check a field device or instrument only to find the field device or instrument hasn't been installed, or the wire and cable hasn't been pulled or terminated, or it's only terminated at one end. So, they have to switch to another loop, often to find a similar situation.)

So, you are good to question--I call it thinking critically. It's good that someone is reading the procedures and finding problems before they become show-stoppers. It makes the procedures that much more usable and credible and reliable, than finding issues when you're trying to actually perform them and regularly finding problems and mistakes. And a word of caution, kindly pointing out mistakes you find will be much more well-received.... That's from painful, personal experience. Remember--most procedures were hastily written, by people who probably don't have that much experience with the equipment. (It's supposed to make them better engineers, remember?) And, there are occasional typographical mistakes, too!

Best of luck! Enjoy. One of the single most important things to be learned during commissioning is: The location of field devices and instruments. The OTHER really important thing to learn is: Valve positioning. There are LOTS of manual valves in plants and they all have to be in a certain position for the plant to start and run reliably. People need to know where these valves are, and what positions they need to be in. Learn to read--AND USE--the P&IDs (Piping & Instrumentation Diagrams)!!! And, where each of the devices on the P&IDs are located. Sitting in front of an HMI isn't where you're going to learn either of the above. And, if you're going to be an operator or technician at the plant, you will have PLENTY of time to sit in front of an HMI. You need to be outside, crawling over the equipment, finding and testing devices ("loop-checking") and learning to use the P&IDs. You need to hear and feel and see equipment working and starting. And that DOES NOT happen sitting in front of an HMI during commissioning.

And, thanks, by the way for the kind words.
As always you are right, without doubts the P&ID is like base, after looking at this you can imagine the whole drawing of system in your head, and what important devices there are in the field or facility.
I would like to say thank you one more time for your detailed description.
 
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