CSA, thanks again! you have validated my trend of thought.

Other concerns are gas quality, and the air/gas ratio for the fixed warm-up FSR.

Lastly..since fired starts and stops are concerns for asset managers. what would be a reasonable number in resolving this sort of problem?

 

David

I'm sorry but I don't understand the last question at all. Asset managers have to deal with the situation that results from the way the units are operated. That's sometimes dictated by some contract or other requirement.

Sure; asset managers would like to limit the number of fired starts and stops (but mostly trips!) but they have to work within the confines of the way the unit is being or has to be operated. If they feel operations could or should do things differently to save maintenance costs they have to "negotiate" with operations, accounting, and management.

There's nothing to be done in the Speedtronic to limit the number of fires starts and stops if that's what you're asking about. And tuning can and should be used to prevent loss of flame on start-up and shutdown.

It should be possible to determine a root cause (or causes) for the loss of flame during start-up. I have seen this happen many times when non-OEM fuel nozzles are installed in a machine. The purchasing manager saved some money (maybe a lot of money) but gave the controls department a headache and are never held accountable (no pun intended). If the fuel nozzles work with no problems, the purchasing department is a hero in the organization. If they have problems, well, the sales guy said they were exactly like the OEM parts and so they must be! The salesman said so.

 

Hello experts

sorry for the cut but i was out of site. i am back now and they are doing a the commissioning phase on the gas line (gas fuel) ....

actually there is a problem on the SRV actuator. the valve began to hummer just before fire and the rippling decreases little after flame it detected. but after speed began to rise, the turbine trip on LOSS OF FLAME.

i noticed that the SRV ref (it goes up to 100% gradually) not equal with the fsgr (lvdt fdk) during start up.

the starts done of course after cold calibration for the valve with suitable gain and null bias curr. (within 5% fdk_ERR)...

we changed the SRV three time and the same prob.
the hydraulic system is fine with pressure levels ,and GCV looks fine and smooth in work..

Any Ideas?

 

"...suitable gain and null bias curr...."

What are the gain and the null bias current values, exactly? If it's not possible to get less than a 5% error between actual, measured physical position (you are measuring actual physical position and comparing that to the reference when checking the accuracy of the calibration, right?) then something is seriously wrong with some configuration value or the servo or the polarity of the applied currents or the servo is not the proper servo for the actuator.

What kind of SRV and GCV are being used? Are they the combined SRV/GCV (two valves in one cast steel assembly, or ???)?

What SRV reference are you referring to? The SRV regulator controls pressure, the P2 pressure, between the SRV and the GCV. The typical signal name for the P2 pressure reference is FPRG. The feedback for the SRV regulator is usually signal name FPG2. When FPG2 is equal to FPRG (in other words, when the feedback is equal to the reference) then the valve is told NOT to change position. Only when the actual P2 pressure is not equal to the P2 pressure reference will the valve be told to move.

If the valve is being told to move, then the actual P2 pressure is not equal to the reference. If the servo current is rising to -100%, then it would seem there is NO P2 pressure feedback, or, there is no gas fuel supply pressure, causing the SRV to go to 100% trying to make the actual P2 pressure (FPG2) equal to the P2 pressure reference (FPRG).

The formula for calculating P2 pressure reference is:

FPRG = (TNH * FPKGNG) + FPKGNO

where FPKGNG and FPKGNO are the "gain" and "offset" Control Constant values.

If the SRV is going to 100% valve position, or even something above, say, 30% valve position during firing and warm-up and the earliest stages of acceleration then it's very likely the gas fuel supply pressure is not correct.

Or, there is some flow restriction in the gas fuel supply line. There should be a y-strainer upstream of the SRV to catch "rocks" and other large items before they go through the gas valves and fuel nozzles. It's very common for this to get plugged, and restrict flow and pressure. Some units have filters upstream of the y-strainer which can become blocked and cause excessive flow restrictions and a very high pressure drop.

Check the gas fuel supply pressure at every point from upstream of the SRV (y-strainer; filters; etc.) to try to determine what's causing a loss of flow/pressure drop.

As for the "hummer", well, that's probably caused by some incorrect configuration values. You haven't told us what kind of Speedtronic is in use at the site.

And, it doesn't seem this is the original poster asking this question.

Anyway, please provide ALL of the requested information to receive any further assistance.

 

Respected CSA has illustrated very well regarding the problem. The user is supposed to mention about Gas Turbine is it standard or with DLN Combustor.

But I would like to add one point that was suffered while commissioning GT Frame 6FA, Machine speed augmentation after 80% speed was very slow and did not self sustain.

On investigation we found GCV downstream witch-hat strainer clogged (welding rods, masking tape etc) were found. After getting strainer clean Machine successfully started.

Hope this will also helpful a little bit.

 

THANKX,

the controller is mark vie with frame 9E DLN turbine, the Gain is set to 1.6 and the null bias is calculated according to servo coil resisters was 3.

the supplied pressure was 25.3 bar and it decrease during the starts up within 7 psi ..

as for the stainer was clean, and the vertical filters got s a a lots of water, because the pipes didn't purged enough from water (after the pipe leak test and cleaning)..

we cleaned the filter and make a gas ventilation (20vs and 20ps opened to air) But still got the same issue.

 

Dear Ahmed

Please do mention how much speed goes and then problem starts?

FSR position, Gas fuel flow FQG-1, P1 value at that moment. Please do check the 20VG-1 behaviour/state as you know after leak test it should be in closed state. if any error in configuration it remains open. it may also cause pressure drop and that will lead to open VSR to wide range.

Hope this will be helpful.

 

Again thanks,

i was really good help from you all.
the problem was the supplied pressure and the incoming water with it. stabilizing p1 and purging the pipe was the trick.

 

also check 96FG2A/2B/2C they are are alike? If two are identical and third one is from different manufacturer that may also lead VSR hunting.

 

Ahmed,

Thanks for the feedback!

This is an excellent example of immediately jumping to the conclusion that a problem is being caused by the Speedtronic. Troubleshooting problems by starting with the assumption that the problem is in or is being caused by the Speedtronic is usually unproductive.

It's MUCH more productive to begin troubleshooting a problem by checking all the external parameters--in this case the gas fuel supply conditions--are as they should be. The Speedtronic is usually very good at controlling the things it can and does control, but when conditions outside of its control are not as they should be the Speedtronic can react in unexpected ways. Which, while it may appear the Speedtronic is not operating correctly once the real cause is determined then it becomes quite clear why it was behaving as it did.

It is recommended that if the Speedtronic servo gain and null bias currents were changed from original as-found values that they be returned to the original as-found values so as not to cause knock-on effects in the future as other operating parameters change.

Again, thanks for the feedback. It's what really makes the posts on the forum valuable for years to come.

 

We installed a Frame 6B GT in 1988 and in 2004 we upgraded our Mark IV to a Mark VI. After that time we seem to have many rocky starts. It would appear to me that after the warm up the acceleration control drives the gas valve too far closed and we loose fire in some of the cans (we have 4 flame scanners). The valve reopens and relights the cans and eventually we make it up to sync in and everything is fine until 18 months later when they shut it down for its maintenance.

I started looking into the control constants to compare what we had in to the specs. I realize the specs are a “starting” point and the field control engineer may have to tweak the numbers a bit. I have been reading the control specs, our manuals and this site to try and understand how the FSRMIN works during acceleration. What I thought I understood in my MAR IV logic was that it did a linear interpolation based on two points (FSKMINU2 and FSKMIND(4)) When I look in my Mark VI logic FSKMINU2 is a 4 point array. So now I’m confused.

Here are some of the “discrepancies” on the control specs<pre>
1988 2004 2004 2013
Mark IV Mark IV Mark VI MarkVI
Spec Found Spec Found

MINIMUM FSR
FSKMIND1 6.6 0.0 5.929 6.6
FSKMIND2 8.,2 8.2 7.366 8.2
FSKMIND3 9.8 0.0 8.800 9.8
FSKMIND4 11.3 0.0 10.6 11.8
FSKMINU2 11.0 0 4.0 4.0
4.0
0.0
0.0

Acceleration Reference during start up

* FSKACC2 25.6 25.6 10.0 10.0</pre>
• the algorithm looks a bit different. On the old Mark IV the error between TNHA and TNHAR was multiplied by 25.6 FSR/N (?) but on the drawing, the multiplication symbol (X in circle) has a -6 next to it. Not quite sure what that means. But in the Mark VI it is just a multiplication sign and the units were %/%/sec.

One other change that the control engineer made in 2004 was that he said our diesel (starting means) was running to fast. We used to crank at 20% turbine speed but now we are at 16% which is 14 HM. On our 2nd start up the other day (first one flamed out), we were having problems and he had them push on the diesel throttle to hold it at 20%. He also had the controls in the FIRE mode for about 10 minutes. He had all four cans and when they went to AUTO it made we still flamed out one can but the turbine held in and the fire came back as it accelerated on up to full speed.

Could someone explain how the minimum FSR works and see if they make any sense of our numbers.

Thanks

 

MWO,

There are a couple of different versions of FSRMIN and the "programming" used to control both start-up and shutdown. But you are on the right track. Sort of.

One of the things that happens is if acceleration is too fast during/after fire/warm-up then when warm-up is complete FSR will go to FSRMIN which may be too low to support maintaining flame in all the combustors.

You need to monitor TNHAR & TNHA during warm-up and acceleration. TNHA should follow TNHAR, but if TNHA is much greater than TNHAR then FSR will be reduced--possibly to FSRMIN--to reduce TNHA to mire closely match TNHAR.
If TNHA is much higher than TNHAR as T2WU approaches K2WU the first thing to try doing is cutting back a little on FSRSU_WU--but not so much that the flame goes out when fuel is cut back from firing. This is all part of the tuning--and sometimes it takes several starts to get it all right.

If that doesn't help reduce the actual acceleration during warm-up without losing flame, then you're going to have to play with the FSKMINDn values--NOT the FSKMINNn values.
Some application code only used two FSKMINDn values during acceleration; some used all four. The trick here is not to increase them by so much that it negatively affects shutdown--because the same Constants are used during shutdown! (Isn't GE great like that? NOT!) if you raise the MINDn values too much then it the unit might not decelerate below a certain speed because the FSRMIN is too high during shutdown--even though it needs to be higher during start-up....

There is yet another concern, too--and that is not to increase the MINDn values so much that the unit accelerates quicker than it should. In other words, the goal is to set a Minimum FSR high enough to prevent loss of flame after warm-up is complete but not so high that the actual acceleration (TNHA) is always higher than the acceleration reference (TNHAR). You just want to prevent loss of flame while FSR is being held at Minimum and TNHA is dropping to match TNHAR.

All while not negatively impacting shutdown or acceleration! And while maintaining flame.

Because of the way GE uses FSRMIN for shutdown and for Minimum FSR during acceleration the tuning can be very time-consuming.

But it should be possible to tune it so that you can maintain flame after warm-up without accelerating it too quickly and let it shut down properly, too. It may take some patience.

During acceleration, FSRMIN is supposed to be set to a value that prevents loss of flame, but sometimes that means acceleration is sometimes a little faster than desired after warm-up is complete, but not for too long.

Please write back to let us know how you fare.

 

CSA,
I appreciate the reply.

There is a general feeling among the operators and mechanical engineer that the blame is based on the diesel speed and it’s lack of ability to hold the speed constant. I assume they are generally built the same.

Our logic has two solenoids 20DA-1 and 20DA-2. When the diesel is warming up, both are de-energized. To get the turbine rolling, 20DA-2 energizes to ramp the diesel up towards full throttle . Once the diesel speed triggers the L14DC, 20DA-2 is de-energized allowing the speed of the diesel to drop. Once l14DC drops out the second solenoid 20DA-1 energizes to hold equal pressure on each side of the cylinder which drives the diesel throttle.

I guess as things heat up, the load on the diesel increases which results in the speed decaying. Prior to the upgrade in 2004, the firing speed was 20% as determined by the diesel logic. The minimum turbine speed was set at 16% as it is now. When the upgrade was made in 2004 to the Mark VI, the control engineer (who admittedly said he had never done a Frame 6) said (in his report) that it was too high should be between 16% and 18% and he lowered it.

In looking at the logic for the diesel I was surprised to find that although the Hold solenoid (20DA-1) was released at the end of the turbine warm up timer, The Acceleration solenoid (20DA-2) was energized two seconds after fire was detected if you are in AUTO or REMOTE.

Additionally whenever the Acceleration solenoid is energized, the Hold solenoid is de-energized. What this means is that the Diesel starts accelerating up after two seconds while the FSR stays at warm up for the full 60 second warm up time. Does this seem correct to you?

If the diesel is ramping up the turbine speed it seems like this could cause the acceleration control to have to initially react harder (driving the FSR down to the minimum fire position). I looked at the old Mark IV logic drawings and this is the way it was built back then also.

Any words of wisdom would be appreciated.

 

MWO,
Certainly a diesel starting means which is not being controlled correctly could be the cause of the problem. The Mark IV was not very good at controlling acceleration during starting, but the Mark VI is much, much better.

There was no clear reasoning for changing the speed level setpoint(s) during the upgrade; it is recommended the speed level setpoint(s) be returned to the previous value(s).

The sequencing you described is normal for starting; the unit is accelerated by the starting means during warm-up, even though the fuel is being held at warm-up value during the warm-up period.

But the fact remains: If the acceleration as the warm-up period expires is too high, the FSR will be cut back to FSRMIN, as calculated by the FSRMIN algorithm. If the calculated value of FSRMIN is too low to support flame then flame will be lost in one or more combustors--and will be evidenced by high exhaust temperature spreads and flickering flame detection or loss of flame until acceleration is reduced to near the acceleration reference, at which time FSR will increase and flame will be restored in those combustors in which it was lost.

So, even if the starting means speed is not stable if the actual acceleration is greater than the acceleration reference FSR will be reduced to the calculated value of FSRMIN--which, if it's too low, will result in flickering flame detection and/or loss of flame indication.

Again, there's no logical reasoning for changing the speed level setpoint(s) during the control system upgrade. The Mark IV was not very (bad, even) at limiting acceleration during start-up, while the Mark VI is MUCH better at doing so--and so acceleration can be problematic after warm-up, requiring adjustment of the MINDn Control Constant values.

Unfortunately, it's mostly a trial and error process which can try the patience of most plant managers/supervisors and operators.

Again, please write back to let us know how you proceed and what the results are.

 

Unfortunately the next opportunity will be in a year so I am trying to compile notes and make a plan while this start up is still fresh on the mind.

The one point that I’m still confused about is that looking at the Minimum FSR arrays for the start up, it appears to me that it is a linear calculation using two points FSKMINU2 @ 40% speed and FSKMIND(4) @ 85% speed. Since the FSKMIND(4) is used in the shutdown array, it would make more sense to me to adjust the slope by increasing the lower point FSKMINU2. This would have the greatest affect on the lower end where I am having the problem and not disturb the SD array.

Am I missing something?

Thanks again for all the help.

 

MWO,

I don't have a copy of Toolbox or a .m6b file for a gas turbine to review. To be specific, it would be necessary to see the .m6b file in use at your site. FSKMINU2 is not used on some applications, so, again--to be specific would require a review of the .m6b file in use at your site.

But, it would seem you are on the right track in analyzing the issue. Just make sure you are reviewing all of the permissives for all of the Control Constants to make sure they are in use in the application code, or not as the case may be.