We're operating a GE Frame 9e DLN turbine,
We recently changed the IGV LVDT and the IGV was working fine giving good feedback after calibration.
The challenge observed was during startup, unit ramps up till immediately after firing, it's observed that the SRV only opens at 6% maximum then goes down to 2% then loss flame and trips.
We calibrated the SRV severally and it opens fully during calibration without drag or hesitation. But when we try to start up it drags between 2, 3,4,5,6%, then trips. What could be the problem?

 

A few things to checks
* Hydraulic pressure ( if your SRV responds fine during calibration the pressure might be ok, but still check and confirm hydraulic oil isn't dumping during startup)
*Servo valve and;
*Servo valve filter( I had a challenge with SRV sometime ago, and the servo valve filter was the culprit)

 

A few things to checks
* Hydraulic pressure ( if your SRV responds fine during calibration the pressure might be ok, but still check and confirm hydraulic oil isn't dumping during startup)
*Servo valve and;
*Servo valve filter( I had a challenge with SRV sometime ago, and the servo valve filter was the culprit)

Thank you Cheedee,
I'll check if the hydraulic oil is dumping, but that's during another startup trial. The servo coils has been checked and they seem okay (3 of them).
For the filter, I'd rather think if filters are clogged, the SRV should rather open more than normal.
Thanks for you suggestion.

 

Sirtaurus12,

WHAT ALARMS ARE BEING ANNUNCIATED PRIOR TO AND DURING THE FIRING ATTEMPT? BOTH Process Alarms AND Diagnostic Alarms.

And, SPECIFICALLY, is the Process Alarm LOSS OF FLAME TRIP being annunciated when the START attempt fails?

How long AFTER flame is established does the loss of flame occur?

The SRV (Stop/Ratio Valve) is driven NOT by a position reference--but by a pressure reference. It's second function is to control the pressure between the SRV and the GCV(s) (Gas Control Valve(s)--we don't know if the unit has one GCV or two or three). The pressure reference signal's name is FPRG (Fuel Pressure Reference-Gas), and there are usually three (3) intervalve (P2) pressure transmitters providing feedback signals to the Mark*. The names of the feedback signals are usually fpg2a, fpg2b and fpg2c. The control system moves the SRV to whatever position is required to make the pressure transmitter feedback equal to the P2 pressure reference.

The P2 pressure reference is a function of the turbine speed. The formula is: FPRG=(TNH*FPKGNG)+FPKGNO. FPKGNG and FPKGNO are both Control Constants (meaning the values can be found in the Control Constants display, and they can be seen using Toolbox when looking at the block that calculates FPRG). If the speed feedback signals from the turbine are not stable and are fluctuating, then the P2 pressure reference will not be stable and it will be fluctuating. And, from the formula it should be clear: The P2 pressure reference (and the actual P2 pressure) will increase as the unit accelerates up to rated speed. And then when the unit is synchronized to a stable grid the P2 pressure reference (and the actual P2 pressure reference) will stabilize--because the shaft speed will stabilize at approximately 100% when it is synchronized to a stable grid. HOWEVER, as the GCVs (Gas Control Valve(s)) open the P2 pressure will tend to decrease but the P2 pressure reference WILL NOT change so the Mark* will open the SRV to maintain the P2 pressure reference.

As an example, the value of the P2 pressure reference during firing is usually somewhere around 2-3 barg--so the SRV moves to whatever position is required by the Mark* to make the P2 pressure feedback from the pressure transmitters equal to the P2 pressure reference. Just because the SRV has LVDTs to indicate it's position does not mean the control scheme for the SRV IS NOT a position control loop--it's a pressure control loop.

The P2 pressure transmitters have a three-way valve (sometimes each transmitter has it's own three-way valve) and the position of those valves is VERY important. There is usually NO indication on the valves or nearby, but the valves have a RUN position, an OFF position, and a VENT position. (The vent position is usually used by technicians for applying a test pressure when verifying the calibration of the transmitter(s).) It's very common for these valves to be put in the wrong position and cause problems, sometimes like this one.

Also, the P2 pressure transmitter feedback for all three transmitters should be as close to each other as possible. (I have read some of your prior threads and it appears the units at your site have Mark VI controllers (you indicated they are Mark VI--not Mark VIe) so the configuration of the P2 pressure transmitters is not certain, because GE changed the configuration during the early years of the Mark VI. But, still, the fact remains that the calibration of the P2 pressure transmitters should be nearly identical.)

Based on the information provided it sounds to me like something is amiss with the turbine shaft speed pick-ups/wiring, or the P2 pressure transmitter feedback (transmitter valve position; wiring; calibration). If the SRV is going open it's important to know what the P2 pressure reference is during firing and what the actual P2 pressure is when the SRV opens, and what happens to the P2 pressure feedback during the firing and "loss of flame" incident.

Based on the description above it's important to ALSO know what's happening to the GCV. The normal sequence of events for the gas valves during firing is that the 20VG-1 solenoid closes as the unit accelerates to firing speed (to close the vent between the SRV and the GCV(s)) and then when it's actually time to start the firing process the GCV (or GCV1) is opened to the firing position (for example, 20%) and then the SRV is opened to bring the P2 pressure up to the P2 pressure reference. Once flame is established the GCV (or GCV1) then closes slightly, for example to 18%, for the "warm-up" period (which is usually 1 minute. If I recall correctly, the Process Alarm LOSS OF FLAME TRIP will NOT be annunciated until after the warm-up period is complete, so it's really important for you to tell us if the alarm is annunciated or not, and to provide a complete list of alarms prior to and during the firing and "loss of flame." Including Diagnostic Alarms. (Record the Diagnostic Alarms existing BEFORE the START attempt, and then AFTER the START failure--and DO NOT let the operators click on DIAG ALM RESET before you record the Diag. Alarms AFTER the START failure!)

IF, after flame is established the GCV closes (fully closes, or closes nearly fully) for some reason, then the P2 pressure is going to increase (as the flow through the GCV decreases) and the SRV is going to close (possibly nearly fully closed) to reduce the P2 pressure.

The resistances of the servo soils are important, but since the servos are bipolar devices the polarity of the current from the Mark* applied to the coils is MOST important. (Negative servo current opens the SRV; positive servo current closes the SRV. All three processors should be applying the same polarity of current when the valve should be opened or closed--and it's a documented fact that the servo manufacturer, and servo refurbishers, do not always reconnect the servo coils exactly the same, hence the need to verify polarity (or rather, the effects of the polarity being applied). There are procedures for verifying the polarity which should be done ANY time a servo is replaced, and the process has been written about MANY times on Control.com. And, replacing a servo DOES NOT require "calibration" of the device; calibration ONLY affects the scaling of the LVDT feedback. AND, if a servo is replaced and the polarity of the servo current is NOT properly verified, then it's very likely that whatever problem caused the servo to be replaced will not be solved, so the time spent replacing the servo (and the lost generation/revenue) AND the cost of the new servo is wasted (except for the feeling it gives some people--which is like wetting yourself while wearing dark pants; it gives you a warm feeling but most other people don't notice).

If you didn't verify SRV servo current polarity, you should. Simply "stroking" the SRV DOES NOT verify servo current polarity, nor does it prove the SRV is working correctly.

You have Mark VI turbine controls, which means you have HMIs with Trender or Trend Recorder. This is very simply the MOST powerful--and easy to use--troubleshooting tool available to you. You should open the Trender/Trend Recorder and create a trend to record the following signals at a minimum:

TNH
TNH1
FPRG
fpg2a
fpg2b
fpg2c
FPG2 (if it exists)
fsrsr
fsrg
(Flame Detector #1 Intensity)
(Flame Detector #2 Intensity)
(Flame Detector #3 Intensity)
(Flame Detector #4 Intensity)
L4
L4T
L28FDA
L28FDB
L28FDC
L28FDD
TTXM
TTXSP1
TTXSP2
TTXSP3

(I don't recall at this writing what the signal names are for the flame detector intensities are, but they can be found using Toolbox. And, the signal names for the P2 pressure transmitter inputs may be different at your site; if so, substitute the correct signals. The same goes for the SRV position feedback (fsrsr) and GCV position feedback (fsrg).)

Run this trend during a START attempt (start it when the purge time ends) and you will have actionable data you can share with others to help you troubleshoot this problem. When the START attempt fails, stop the trend and SAVE THE FILE!!!

Another amazing feature of Trender/Trend Recorder is that it records alarms (YES!!!) permanently and stores the alarms with the data it recorded--which can be VERY helpful to others viewing the information.

Learn to use Trender/Trend Recorder. Practice using it by recording starts and shutdowns. You can use the data from good STARTs to troubleshoot failed or problematic STARTs. It is a VERY POWERFUL and under-used FREE resource (it is provided with the software on the HMI).

 

Wow

Sirtaurus12,

WHAT ALARMS ARE BEING ANNUNCIATED PRIOR TO AND DURING THE FIRING ATTEMPT? BOTH Process Alarms AND Diagnostic Alarms.

And, SPECIFICALLY, is the Process Alarm LOSS OF FLAME TRIP being annunciated when the START attempt fails?

How long AFTER flame is established does the loss of flame occur?

The SRV (Stop/Ratio Valve) is driven NOT by a position reference--but by a pressure reference. It's second function is to control the pressure between the SRV and the GCV(s) (Gas Control Valve(s)--we don't know if the unit has one GCV or two or three). The pressure reference signal's name is FPRG (Fuel Pressure Reference-Gas), and there are usually three (3) intervalve (P2) pressure transmitters providing feedback signals to the Mark*. The names of the feedback signals are usually fpg2a, fpg2b and fpg2c. The control system moves the SRV to whatever position is required to make the pressure transmitter feedback equal to the P2 pressure reference.

The P2 pressure reference is a function of the turbine speed. The formula is: FPRG=(TNH*FPKGNG)+FPKGNO. FPKGNG and FPKGNO are both Control Constants (meaning the values can be found in the Control Constants display, and they can be seen using Toolbox when looking at the block that calculates FPRG). If the speed feedback signals from the turbine are not stable and are fluctuating, then the P2 pressure reference will not be stable and it will be fluctuating. And, from the formula it should be clear: The P2 pressure reference (and the actual P2 pressure) will increase as the unit accelerates up to rated speed. And then when the unit is synchronized to a stable grid the P2 pressure reference (and the actual P2 pressure reference) will stabilize--because the shaft speed will stabilize at approximately 100% when it is synchronized to a stable grid. HOWEVER, as the GCVs (Gas Control Valve(s)) open the P2 pressure will tend to decrease but the P2 pressure reference WILL NOT change so the Mark* will open the SRV to maintain the P2 pressure reference.

As an example, the value of the P2 pressure reference during firing is usually somewhere around 2-3 barg--so the SRV moves to whatever position is required by the Mark* to make the P2 pressure feedback from the pressure transmitters equal to the P2 pressure reference. Just because the SRV has LVDTs to indicate it's position does not mean the control scheme for the SRV IS NOT a position control loop--it's a pressure control loop.

The P2 pressure transmitters have a three-way valve (sometimes each transmitter has it's own three-way valve) and the position of those valves is VERY important. There is usually NO indication on the valves or nearby, but the valves have a RUN position, an OFF position, and a VENT position. (The vent position is usually used by technicians for applying a test pressure when verifying the calibration of the transmitter(s).) It's very common for these valves to be put in the wrong position and cause problems, sometimes like this one.

Also, the P2 pressure transmitter feedback for all three transmitters should be as close to each other as possible. (I have read some of your prior threads and it appears the units at your site have Mark VI controllers (you indicated they are Mark VI--not Mark VIe) so the configuration of the P2 pressure transmitters is not certain, because GE changed the configuration during the early years of the Mark VI. But, still, the fact remains that the calibration of the P2 pressure transmitters should be nearly identical.)

Based on the information provided it sounds to me like something is amiss with the turbine shaft speed pick-ups/wiring, or the P2 pressure transmitter feedback (transmitter valve position; wiring; calibration). If the SRV is going open it's important to know what the P2 pressure reference is during firing and what the actual P2 pressure is when the SRV opens, and what happens to the P2 pressure feedback during the firing and "loss of flame" incident.

Based on the description above it's important to ALSO know what's happening to the GCV. The normal sequence of events for the gas valves during firing is that the 20VG-1 solenoid closes as the unit accelerates to firing speed (to close the vent between the SRV and the GCV(s)) and then when it's actually time to start the firing process the GCV (or GCV1) is opened to the firing position (for example, 20%) and then the SRV is opened to bring the P2 pressure up to the P2 pressure reference. Once flame is established the GCV (or GCV1) then closes slightly, for example to 18%, for the "warm-up" period (which is usually 1 minute. If I recall correctly, the Process Alarm LOSS OF FLAME TRIP will NOT be annunciated until after the warm-up period is complete, so it's really important for you to tell us if the alarm is annunciated or not, and to provide a complete list of alarms prior to and during the firing and "loss of flame." Including Diagnostic Alarms. (Record the Diagnostic Alarms existing BEFORE the START attempt, and then AFTER the START failure--and DO NOT let the operators click on DIAG ALM RESET before you record the Diag. Alarms AFTER the START failure!)

IF, after flame is established the GCV closes (fully closes, or closes nearly fully) for some reason, then the P2 pressure is going to increase (as the flow through the GCV decreases) and the SRV is going to close (possibly nearly fully closed) to reduce the P2 pressure.

The resistances of the servo soils are important, but since the servos are bipolar devices the polarity of the current from the Mark* applied to the coils is MOST important. (Negative servo current opens the SRV; positive servo current closes the SRV. All three processors should be applying the same polarity of current when the valve should be opened or closed--and it's a documented fact that the servo manufacturer, and servo refurbishers, do not always reconnect the servo coils exactly the same, hence the need to verify polarity (or rather, the effects of the polarity being applied). There are procedures for verifying the polarity which should be done ANY time a servo is replaced, and the process has been written about MANY times on Control.com. And, replacing a servo DOES NOT require "calibration" of the device; calibration ONLY affects the scaling of the LVDT feedback. AND, if a servo is replaced and the polarity of the servo current is NOT properly verified, then it's very likely that whatever problem caused the servo to be replaced will not be solved, so the time spent replacing the servo (and the lost generation/revenue) AND the cost of the new servo is wasted (except for the feeling it gives some people--which is like wetting yourself while wearing dark pants; it gives you a warm feeling but most other people don't notice).

If you didn't verify SRV servo current polarity, you should. Simply "stroking" the SRV DOES NOT verify servo current polarity, nor does it prove the SRV is working correctly.

You have Mark VI turbine controls, which means you have HMIs with Trender or Trend Recorder. This is very simply the MOST powerful--and easy to use--troubleshooting tool available to you. You should open the Trender/Trend Recorder and create a trend to record the following signals at a minimum:

TNH
TNH1
FPRG
fpg2a
fpg2b
fpg2c
FPG2 (if it exists)
fsrsr
fsrg
(Flame Detector #1 Intensity)
(Flame Detector #2 Intensity)
(Flame Detector #3 Intensity)
(Flame Detector #4 Intensity)
L4
L4T
L28FDA
L28FDB
L28FDC
L28FDD
TTXM
TTXSP1
TTXSP2
TTXSP3

(I don't recall at this writing what the signal names are for the flame detector intensities are, but they can be found using Toolbox. And, the signal names for the P2 pressure transmitter inputs may be different at your site; if so, substitute the correct signals. The same goes for the SRV position feedback (fsrsr) and GCV position feedback (fsrg).)

Run this trend during a START attempt (start it when the purge time ends) and you will have actionable data you can share with others to help you troubleshoot this problem. When the START attempt fails, stop the trend and SAVE THE FILE!!!

Another amazing feature of Trender/Trend Recorder is that it records alarms (YES!!!) permanently and stores the alarms with the data it recorded--which can be VERY helpful to others viewing the information.

Learn to use Trender/Trend Recorder. Practice using it by recording starts and shutdowns. You can use the data from good STARTs to troubleshoot failed or problematic STARTs. It is a VERY POWERFUL and under-used FREE resource (it is provided with the software on the HMI).

Wow CSA,
You're indeed something in this business and I'll have to pick my notepad and pen to take note then answer most of your questions.
Thank you so much.
We decided earlier to change the servo valve (MOOG) as well as its filter just as Cheedee suggested then tried starting up and it did actuate properly after firing.

Thanks so much for your help.

 

Sirtaurus12,

The SRV--because its purpose is to control P2 pressure and it will go to whatever position it needs to go to in order to make the actual P2 pressure equal to the P2 pressure reference--will not "snap" open (like the GCV does) during firing. If it did that, the P2 pressure would likely be too high very quickly, which would then cause the SRV to close (quickly) and set up a hunting (oscillating) condition. The gas fuel supply pressure should be somewhere around 20+ barg, so the pressure upstream of the SRV is "high" and the desired P2 pressure during STARTing is pretty low (2-3 barg, usually), and the GCV is only going to be approximately 20% open (as an example), so there won't be a lot of flow through the GCV initially. The SRV usually opens rather slowly during firing to increase the P2 pressure slowly (again, the upstream supply pressure is 20+ barg, and the P2 pressure reference is only about 2-3 barg, usually), so the SRV shouldn't have to open very much to raise the P2 pressure to 2-3 barg when the upstream supply pressure is 20+ barg and the GCV is only about 20% open or so.

Once flame is established, then FSR is cut back (meaning the GCV closes slightly, usually just a couple of percent) to reduce the fuel flow-rate to minimize the flame temperature inside the turbine (and the exhaust temperature spike). Sometimes when this happens, there is some flickering of the flame intensities and sometimes individual combustors lose flame (remember, only four of the combustors have flame detectors). And, after the 1 minute warm-up period (typically), the GCV begins to ramp open to increase the acceleration of the unit.

Sometimes, if the unit is accelerating during the warm-up period, the actual acceleration rate exceeds to acceleration rate reference, and when this happens sometimes the GCV is not opened at the end of the warm-up period, but it is closed--and closed too much, and this causes the flame to be lost. THIS usually results in a LOSS OF FLAME TRIP alarm and trip because it occurs AFTER the warm-up period is complete. This can usually be handled with some "tuning" but it's NOT all just Control Constants.

Anyway, I just read you replaced the SRV servo and all is well! (Thanks for feedback!!!) That's great news!! Servos usually fail because of dirty oil.... Oil cleanliness is critical to proper servo operation. Sometimes, some hydraulically-operated devices have filters upstream of the servos, called "last-chance filters" (because they are the last filter before the servo). Most servos also have small internal filters called "pencil filters" (because they are very thin and round) which can be removed, cleaned and replaced, or just replaced--but you need to know where the access is or you will screw up the null bias setting of the servo.

And, verifying servo current polarity is also VERY important when replacing a servo. "Calibrating" the device does NOTHING to the servo; it only affects LVDT feedback, so if nothing else was done to the device or the LVDTs when the servo is replaced, "calibrating" the device is a waste of time. It's MUCH more important to verify the servo current polarity (which requires the use of the calibration utility). Sure, the coil leads are individually colored, but I have seen brand new servos out of the box which had the right colors on each of the three coils--but on one or two of the coils the connections inside the servo were reversed, and that cause the polarity of the current being applied to the coil from the Mark* to be opposite of what it should be. Which can cause problems, especially if two coils are wired "backwards."

Anyway, congratulations! And, thanks again for the feedback.

 

Wow


Wow CSA,
You're indeed something in this business and I'll have to pick my notepad and pen to take note then answer most of your questions.
Thank you so much.
We decided earlier to change the servo valve (MOOG) as well as its filter just as Cheedee suggested then tried starting up and it did actuate properly after firing.

Thanks so much for your help.

CSA is on another level!!!! I and some colleagues have come to the conclusion that CSA might be an Andriod or at least 3 different people

 

Well, ..., I did stay at a Holiday Inn Express last night.

And, I do have Android phones.

And, I've been doing this for more than 35 years; I should have learned something in that time.

I'm just fortunate that I seem to be able to explain things to people (well, sometimes). I always try to remember what it was like when I started and I didn't know what (or where) a compressor bleed valve was (or did), and I was sent to Mark IV school without any mechanical or controls experience. I asked SO MANY questions the instructor told me I would NEVER make a good controls engineer or start-up engineer.

A colleague used to say, "It's not rocket science." It seems like it is in the beginning, and the tribal knowledge stuff makes it worse. Plus the lack of documentation from the OEM. I would write a book, but it would be scanned and made available on the World Wide Web in no time, so my time and effort would be for naught.

Thanks for the kind words, everyone.