The unit is frame 5 with Mark V control systems.

The unit was running for more than 18 hours with 8MW load after GCV/SRV maintenance and recalibration. this morning we did shutdown for oil leak. And during the start up at the FSNL the speed continue to increase till overspeed trip. at the same time I used the Manual FSR control to bring down the speed and to avoid the over frequency trip.

I can see the speed goes up to 5346 rpm,

We did the SRV & GCV calibration yesterday and the unit was started two times without any problems. today we did the P2 pressure transmitter calibration check only and the problem started. customer is asking to recalibrate the P2 transmitters which I don’t agree on

Looking forward for your assistance

 

First question has got to be where was the TNR? At FSLn was the FSR on Speed Control, if not, what was controlling FSR?. Did you have any SRV or GCV diagnostics? Any more info would be helpful Where was the P2 pressure during this speed increase, was it on the set-point?

 

> ....the speed continue to increase till overspeed trip. at the same time I used
> the Manual FSR control to bring down the speed and to avoid the over frequency [sic] trip.

It's not clear if the unit tripped on overspeed (it wouldn't trip on over-frequency if the generator breaker were open) or not.

What Process- and Diagnostic Alarms were annunciated when the inability to maintain FSNL occurred?

You said the SRV and GCV were "out for maintenance". What was done to them? Was the hydraulic actuator replaced? Were the valve disassembled and new or refurbished parts used in reassembly? Were new shaft seals installed? Were the servo-valves replaced?

It would seem that if you were able to use Manual FSR to limit the GCV opening that the GCV was not sticking and was able to be controlled by the Mark V. Did you try using the LOWER SPD/LOAD target to try to reduce speed? If so, did it work?

The real mystery is: Why didn't the Mark V close the GCV to maintain FSNL? You were able to do so with Manual FSR, so why didn't the Mark V do it?

If the SRV was not able to control P2 pressure--for whatever reason--then it would seem that the Mark V should see the excess fuel flow through the GCV and close the GCV to reduce speed.

The only thing I can think of is if the unit uses the "pure" or "straight" Droop Speed Control which has a single value for FSNL FSR: FSKRN1, if I recall correctly. You would need to look at the CSP to see if the unit uses Droop Speed Control or Constant Settable Droop Speed Control, because the Control Constant FSKRN1 will exist and it will have a default value even if the unit DOESN'T use straight Droop Speed Control (it's that "Max Case" thing; isn't that fun? NOT!).

And, if the unit uses straight Droop Speed Control (FSRN=[(TNR-TNH)*FSKRN2]+FSKRN1) then if the P2 pressure were too high then the speed might not be properly controlled. The rate of speed increase would be a function of how much higher the actual P2 pressure was versus the P2 pressure reference.

MANY times when gas valve maintenance is done, the P2 pressure sensing valves are NOT put in the proper position before the unit is started. Also, if there is a three-way valve used for the pressure sensing line to the transmitter, with the "branch" going to an atmospheric vent, many times after calibration these valves are not put in the proper position, also.

If it was necessary to make a "large" adjustment in the calibration(s) of the P2 pressure transmitter(s), then I would say the calibration is suspect. They don't usually drift a lot, so if a "large" change was necessary (which should be listed on the calibration data sheet, where the as-found condition(s) and the as-left condition(s) should BOTH be recorded) then it would seem something was amiss with the calibration procedure, or the tubing/valving.

My money (if we were betting) would be in improper valving/tubing after the "calibration." It costs nothing to ensure the valving and tubing is in the right position. Next would be P2 pressure transmitter calibration, and then only if "large" changes were made during "calibration."

All of the above is only true if the unit as the "straight", "classical" Droop Speed Control. If the unit uses Constant Settable Droop Speed Control, then the Mark V should have been able to automatically close the GCV to maintain FSNL even if the P2 pressure wasn't correct.

One other thing which might have happened or be happening is that 20VG-1 isn't seating properly. This happens occasionally, but not very often, and a leaking 20GV-1 can cause improper P2 pressure. Regardless of which version of Droop Speed Control is in use.

If the unit wasn't on Droop Speed Control when it reached 100% speed (and that would likely have a Process Alarm to alert the operator to the condition, but since the unit didn't trip most operators just ignore alarms--they're just nuisances, anyway, right?) then it wouldn't necessarily be controlling speed. But, you didn't tell us what alarms were annunciated or active at the time of the event.

Lastly, this is a good of example of a mindset to use "forcing" to solve every problem. Did you try using LOWER SPD/LOAD to reduce the GCV position (by lowering TNR), or did you just rush to the FSR Control Screen and use Manual FSR to limit GCV position? This is very typical, but not a good example for operators/technicians. Manual FSR is "forcing" the GCV to be something less than it would otherwise be, and "forcing" things is not always the proper answer, and not always the proper example.

But, one does what one "has" to do, right?

 

Thanks for ur feedback....will follow ur instructions and update u shortly....

Here is my comments;
The unit started on Auto mode and on Droop governor mode and tripped on over frequency with generator breaker open, the first alarm came was the OVERFREUENCY RELAY.

THE first action take is lower the speed by local manual lower which is not responding even the Raise not responding, then tried to change from Droop governor control to Isoc. Without any respond. Finally was the Manual FSR. NO DIGNOSTIC ALARM RELATED TO SPEED CONTROL OR SPEED PICKUP OR SRV\GCV SERVO CURRENT OR FEEDBACK.

The two trip alarms were: OVERFREQENCY RELAY FOR 52G TRIP AND GENERATOR LOCKOUT RELAY-FULL SPEED NO LOAD.

Both SRV&GCV valve were refurbished, all the internal parts changed and the actuators and the LVDTs except the Servo valves. The gab was sited to 0.50mm.

FPG2 in the pre vote data are matching but it looks like high than the normal, its 218PSI at FSNL before start increasing the speed and its 226 at 103.7% of speed.

FPG2 AND FPRGOUT ARE MATCHING!

One more thing FSR manual control works for Shutdown too up to 20% of speed flame out which is not working by the Normal shutdown the unit ramp down and stays at 91.47% NOT GOING DOWN then trips by SD time out (K94XZ)

 

It's very interesting that the unit would trip on overfrequency when the generator breaker was open. Just questioning "out loud," why would it matter if the frequency was higher than rated when the generator breaker was open? The unit isn't supplying any load (unless the unit is a "black start" unit.?.?.?) so the frequency shouldn't be a problem.

FPRG = (TNH * FPKGNG) + FPGNO

The formula says, the reference is a function of speed--which is what the Speed/Ratio Valve does, secondarily: control P2 pressure as a function of speed. When speed is increasing, so will the P2 pressure reference. So, that's kind of to be expected.

You say the unit doesn't go on fired shutdown. I think this may be the crux of your problem. It sounds like Minimum FSR is set WAY TOO HIGH and is affecting FSNL FSR as well as Shutdown FSR.

You need to monitor FSRMIN and FSRN and FSRSD (the latter during a shutdown after the generator breaker opens). I think you will find that the FSRMIN array Control Constants are set too high, and that's causing the problems you are seeing. Changing the gas valve components has probably caused a change in the amount of gas flowing for a given GCV position and that is requiring a review of the FSRMIN array values.

FSRMIN was probably a borderline issue before the gas valves were refurbished. Now that they've been refurbished and the flow-rates through the valves have changed (for whatever reason--non-spec internals, or slightly different internals, or a large difference in GCV calibration values before the valve refurbishment and after the valve refurbishment) the problem has finally "come to light."

DO NOT change the speed level Control Constants! They are usually set at something like 40% and 70% and 80% and 90% or something like that. But those values (FSKMINNn, I think--I don't have a Control Specification or an .m6b file to look at at this writing) SHOULD NEVER BE CHANGED!

It's the other values, FSKMINDn, I think (I may have them reversed; sorry if I do!) that need to be lowered. That will help with the fired shutdown and will also probably help with the FSNL FSR as well.

Decreasing the FSR values of the FSRMIN array may result in an excessive deceleration during a fired shutdown, and even a loss of flame before 20% speed. So, be aware that changing them by too much may also have an undesired effect.

Also, if the unit has a requirement to maintain flame on load rejection, reducing the FSRMIN values by too much may result in a loss of flame on load rejection....

Please write back to let us know what you find--especially with respect to FSRMIN versus FSRN at FSNL, and FSRMIN vs. FSRSD during shutdown!

 

The formula below has a typographical error; sorry for any confusion.

>FPRG = (TNH * FPKGNG) + FPGNO

It should read:

FPRG = (TNH * FPKGNG) + FP<b>K</b>GNO

 

Thanks CSA for your support...

The unit started after tunning the above mentioned constanat two times this afternoon with no trouble with 2MW test load. Smooth firing and start up FSNL setting was 100.3%-5120Rpm- 60 Hertz.
And the Shut down ramp was smooth up to 17.08% speed-872Rpm for 7min time (Flame out setting).<pre>
These are the final setting:
FSKMIND1 7.88 %
FSKMIND2 9.85 %
FSKMIND3 11.80 %
FSKMIND4 14.45 %
FSRMINU2 14.04 %</pre>

 

Teetto TA,

You are most welcome--and thanks for the feedback!

I'm not quite sure I understand why it was necessary to change FSKMINU2.... Can you explain?

 

Mr.CSA,

I am facing the same problem with GE MS5001 turbine made by N.P.with control MK6 and MK6e. MK6e is working as safety instrumented system.

unit was running normally till we got a trip because of loss of flame. We checked every thing and finally we found that 20FG1 solenoid valve is not working. After replacing 20FG1 unit was running normally then we did normal shutdown to the unit because we did not need to load it.

two days later we started the turbine but we got a problem with FSNL speed which was about 5350 RPM.

we checked the P2 probe and transmitters but nothing was wrong with them. next day we start the turbine and got over speed trip with about 5457 RPM and the SRV opening was about 55% which is too high. can you help me please because I am alone and I am the only control engineer at this site.

Thanks for help

 

Ghaith,

Have you checked the same Control Constants as recommended above? What are the present values of those Control Constants?

What happened to the original poster was that the GCV wouldn't close to limit speed to 100% (FSNL). Since the SRV P2 pressure reference is a function of turbine speed, as the speed increases so will the P2 pressure reference--and the actual P2 pressure. Even if the GCV is being held at a constant position, as the actual P2 pressure increases the flow through the GCV will increase. As the flow increases, the speed will increase. As the speed increases, the P2 pressure reference will increase. Left unchecked, the increasing speed will cause the P2 pressure to keep increasing which will cause the speed to keep increasing.

The problem is most likely not the SRV--it's the Control Constants that set the minimum stroke position for the GCV. If the minimum GCV stroke position is too high, and the GCV can't close to limit speed, then exactly what you are experiencing is going to happen.

Unfortunately, without a LOT more data it's going to be very difficult to help you quickly. You would need to provide all of the values of the Control Constant arrays that set the Minimum FSR position (because it's a calculated value under normal conditions, with a hard minimum setpoint under other conditions).

Having said all of the above, it's difficult to understand why this problem started after the unit had been running without any problems. It would seem that someone had made some changes during the original troubleshooting and forgot to reset the values.?.?.? Or, someone attempted to "re-calibrate" the SRV and/or the GCV LVDTs.?.?.? Or someone replaced a servo-valve on the GCV or SRV.?.?.?

Lastly, you didn't provide any information about the servo currents during the overspeed condition. Were they "higher" (more negative) than normal, indicating a sticking SRV servo, or a sticking GCV servo? While not likely, it could be that two or more problems have combined at relatively the same time to cause the issues you are seeing.

 

Mr. CSA

Thanks for your help

today I downloaded another software to the control system which I took from the HMI about 3 months ago when the unit was running normally.

now, There is no over speed on the turbine but the lower and raise buttons are not affecting on the turbine speed , Also I have a difference between the speed reference and the actual speed ,

What I did is trying to lower the speed from GCP but also lowering was not possible

The values for the control constants is as follow:

FSKMIND1 10.5
FSRMIND2 13.1
FSRMIND3 15.2
FSRMIND4 18.2

FSRMINU2 17.6

These values are the same as the other unit which is working normally

 

Ghaith,

Mark VI dynamically assigns signal names to memory locations, which can lead to the kind of problem you are experiencing with downloading "old" software.

I still highly recommend you get someone knowledgeable to site to help with the problem(s) you are experiencing. There is more to this story than we know, and someone on site can get the whole story and help with resolving the problem.

I wish I could have been more help, but the problem definition has now changed. As such, it's very difficult to understand what has happened, what is happening, what has been done and what has not been done.

GE HMIs and Mark VI/VIe (even Mark V) are very "touchy" systems that have be very carefully matched in order for everything to work properly. If you downloaded some older software to the Mark VI, but didn't update the hmb file and CIMPLICITY Project, then you can very well experience the problems you are seeing. But, <b>that's only from the information provided,</b> and I have a strong feeling there is more information than is being provided.

Unfortunately, there is no checklist of how to make the two systems (HMI and Speedtronic Mark panels--because they are two different systems that have to work together to control, protect and monitor a turbine and its driven device and auxiliaries) work together. Worse, the steps change depending on which versions of CIMPLICITY, Toolbox, TCI and other applications and programs. Worse still, if you have multi-unit HMIs for more than one Speedtronic panel at site, then things can get very complicated very quickly.

Please have someone knowledgeable come to site to assist with the problems you are experiencing. It will be money well spent.

 

Mr.csa ,

Thanks for your help. the problem had been solved. when I thought about turn the power off for both MK6 and MK6e for about two hours then power up both controller and every thing is going fine now and unit is loaded with 15MW.

Thanks for your support again

 

Ghaith,

Thanks for the feedback!