FSR Manual Control GE Frame 7E


If the GTG unit have load restriction (for any reason), then the Operator takes Unit control in FSR MANUAL mode and keep unit at fixed MW below the restricted value (MW), until the problem fixed.

1. Does frequency excursion have any impact on GTG operation at fixed MW in FSR Manual mode operation?

2. If yes, what are the possible impacts?

3. How long can we keep the unit on FSR manual mode? Is there any guidance OEM provided for FSR Manual mode operation?

4. Please also clarify the use of FSR manual mode (In general)

Thank you


It's important to understand precisely how the unit is being operated in "MANUAL FSR" control at your site to be able to answer your question.

Please explain precisely how the operator "...takes Unit control in FSR MANUAL mode..." Is the operator using the FSR "GAG" function on the FSR display of the operator interface?

Or is the operator just using the RAISE- and LOWER SPEED/LOAD buttons to control the load until such time as Pre-Selected Load Control can be re-enabled?

I'm presuming the normal mode of operation is to use Pre-Selected Load Control (which is NOT the way a unit should be operated if it experiences grid frequency disturbances, anyway).

So, please provide the details of what the operator does to place the unit in "MANUAL FSR" control and how the operator loads/unloads the unit to achieve a desired output while on "MANUAL FSR" control. And then how the operator releases "MANUAL FSR" control.
Still we didn’t apply the manual FSR. May be the question makes different.
The unit has load restrictions and we need to apply the manual FSR but we never did it. So we need to know
When do we need to apply?
As per our understanding that when the unit on FSR manual it won’t respond to the frequency during the excursion and It will be on the fixed MW?

Hope the issue is clear now.

I apologize for adding to the confusion.

1) Do you now primarily operate the unit using Pre-Selected Load Control when there is no need for curtailment?

2) When curtailment is necessary, are you proposing to use the RAISE- & LOWER SPEED/LOAD buttons to reduce and maintain load, referring to this method of controlling load as ”Manual FSR” control? If not, please explain what you are referring to as ”Manual FSR” control?

The reason I am being so particular about this is because there is something formally called ”Manual FSR” in Mark* heavy duty gas turbine control systems. It's NOT something operators typically use; it's primarily used for troubleshooting or emergency situations.

I believe what you are referring to as ”Manual FSR” control is Droop Speed Control. Using (clicking on) the RAISE- or LOWER SPEED/LOAD buttons >>does<< change FSR, but it does so by changing the Turbine Speed Reference which changes the error between the Turbine Speed Reference and the actual turbine speed which affects FSR.

Pre-Selected Load Control is an added outer loop to Droop Speed Control, which compares the Pre-Selected Load Reference to the actual load and then changes the Turbine Speed Reference to ultimately change FSR (by again changing the error between the Turbine Speed Reference and the actual turbine speed).

SO MANY people firmly believe that a GE-design heavy duty gas turbine is to be NORMALLY operated at all times when loaded using Pre-Selected Load Control. NOT!!!

Your questions about grid frequency and ”Manual FSR” control imply that the unit is somehow being controlled better or somehow more protected when it's on Pre-Selected Load Control. And that the unit is unprotected and in some kind of danger when not being operated using Pre-Selected Load Control.


Full stop. Period.

Pre-Selected Load Control enabled during grid frequency excursions is bad for the turbine and load coupling--but it's worse for the grid! Because the turbine and generator are doing the exact opposite of what they are supposed to do during grid frequency disturbances which only makes the disturbance worse, for everbody.

Most operators, their supervisors and many Plant Managers believe that during a grid frequency disturbance the unit(s) at their site should not have load fluctuations (some even believe the frequency of the unit(s) at their site should not change, either). That belief is completely unfounded and reflects a deep misunderstanding of Droop Speed Control and basic AC (Alternating Current) power systems and generation.

Many grids now are forbidding the use of Pre-Selected Load Control, saying the unit(s) must be operated in ”Free Governor Mode”--which is what I believe you are referring to as ”Manual FSR” control.

The topic of Droop Speed Control has been covered many, Many, MANY times before on control.com.

Again: There is a function in Mark* heavy duty gas turbine control systems called ”Manual FSR” but it's intended as a troubleshooting or emergency operating method; most operators and many Instrumentation & Control technicians don't even know it exists. It WOULD NOT be a good idea to use it during normal operation whether or not there was some kind of load restriction or curtailment.

Pre-Selected Load Control was never intended to be a full-time, normal operating mode. If it had been it would have operated differently than it does (and it should have operated differently than it does to prevent its use as a normal operating mode). Many grid operations companies and governments are forbidding its use without modification to allow proper response to grid frequency disturbances.

Hope this answers your questions, and it would still be great if you could describe precisely what you mean by”Manual FSR” control. Because I don't believe the real Manual FSR control is what you really mean--and if it is, well, don't use it for what you're intending. You'll be sorry you did.
Dear kindly see below feedback on your questions.

My feedback
  1. 1. Do you now primarily operate the unit using Pre-Selected Load Control when there is no need for curtailment?
    Answer: NO, we operate the unit most time by either speed /load or exhaust temperature control mode.
  2. 2. When curtailment is necessary, are you proposing to use the RAISE- & LOWER SPEED/LOAD buttons to reduce and maintain load, referring to this method of controlling load as ”Manual FSR” control? If not, please explain what you are referring to as ”Manual FSR” control?
Answer: For Manual FSR ,We have two target buttons as FSR-GAG PRE-SET & FSR-GAG SET-POINT in the sub menu (Fuel Control) of User Define Display menu.please see the attached snapshot. FSR manual control is an open loop fuel control used to suppress the fuel stroke reference in the FSR minimum select gate algorithm. The FSR set point is preset at FSRMAX, out of the way. The FSRMAN below FSRMAX alarms indicating that the FSRMAN is not at the maximum value. The set point may be adjusted with the following two methods: set point, or the preset button, which sets FSRMAN equal to FSR.

So, our question remain same as specified in the first post.FSR-1.png

Answer: No. ”Manual FSR” control IS NOT the proper way to restrict load. The word ”gag” in this context means to limit by reducing or ”clamping.” In other words, if FSR is 59.6% and you reduce it to 48% using ”Manual FSR” control you are suppressing FSR and preventing it from being 59.6%. Droop Speed Control or exhaust temperature control would be trying to maintain 59.6% FSR but ”Manual FSR” control would be preventing it from being 59.6%.

If there was a grid frequency decrease and the unit was previously operating in Droop Speed Control at Part Load before ”Manual FSR” control was applied the Mark* would be trying to increase FSR to support grid stability--but ”Manual FSR” control would prevent that from happening.

As I previously wrote, ”Manual FSR” control is only intended for troubleshooting purposes--never for normal operation. For example if the grid frequency was stable but the unit load was unstable and constantly increasing and decreasing and increasing and decreasing by 3 MW (for a total swing of 6 MW) and you wanted to troubleshoot the problem to determine if the instability was caused by the Gas Control Valve actuator/servo or the Stop/Ratio Valve actuator servo or gas fuel pressure instability one might use FSR control to temporarily reduce FSR to try to stop the instability. If the instability didn't stop or wasn't reduced then the problem is most likely the Gas Control Valve actuator or servo. But if the load instability was stopped or significantly reduced by gagging FSR with “Manual FSR” control but the P2 pressure was still unstable or the gas fuel supply pressure was still unstable then the problem is most likely the gas fuel supply pressure or the Stop/Ratio Valve control or the SRV actuator/servo. ”Manual FSR” is simply a way of trying to stabilize fuel flow to understand what the cause of unstable fuel control valve operation might be.

”Manual FSR” control could also be used on the liquid fuel control valve to try to determine the cause of load instability (either the liquid fuel control valve or liquid fuel supply pressure instability, for example).

”Manual FSR” control was never intended to be used for reducing fuel flow to reduce load even for just a few minutes and certainly not for an hour or more, especially if the grid the unit is synchronized to is subject to frequency excursions, particularly low grid frequency when generators are supposed to increase power output to support grid stability but FSR is being gagged using ”Manual FSR” control.

Just use the LOWER SPEED/LOAD button on reduce load when there is restriction or curtailment--that way if there is a grid frequency disturbance the Mark* can respond appropriately.

Will using ”Manual FSR” control hurt or damage the unit in any way? No. But using it for simple load reduction as you are proposing is an improper use of ”Manual FSR” control.

In more than 30 years of turbine control work I can have not used ”Manual FSR” control more than twice, and both times it was only for a brief period of a couple of minutes or less and both times it was not useful in discovering what the cause of load instabilities were. It's intended to be used as an electronic method of limiting or clamping or gagging the Gas Control Valve or liquid fuel control valve for short periods of time for troubleshooting. Imagine having a physical clamping device you could apply to the fuel control valve and use it to reduce fuel flow and/or keep the valve from opening more than a certain amount. That's what ”Manual FSR” control is for.

I believe when the engineers who were designing the first digital, microprocessor-based Mark* turbine control system realized some of the possibilities of the system they got a little too excited and added this feature. I have only used it twice myself, and have only heard of it being used by someone else once. If you had a physical fuel control valve clamping device how often do you think you would use it? :unsure:

Hope this helps! Thank you for clarifying what you were asking about. Many people invent names for things, some of which are already in existence but seldom used--or just don't exist. This is a technical forum and we should be certain we are all talking about and discussing the same things.
Thanks for your kind and detailed reply.

Let me explain our entire scenario.

We have many GTG units connected with the grid.

If one of the unit have restriction (mechanical, electrical etc. example Lube oil cooler problem), we cannot increase load beyond certain MW. If the grid frequency decreased, speed droop control will try to increase unit load, so unit might trip on lube oil temperature high.

In order to avoid unit trip in such situation, until we fix the Lube oil cooler problem, we need to fix the unit load at safe MW value.

This unit, we do not want it to response to any frequency excursion. While other GT units available to respond to the frequency disturbance.

If we do not restrict the sick unit by the manual FSR at desired load, we might lose this unit, which further impact on the grid frequency stability. We need to perform load restriction on temporary basis until the problem being resolved. We will also, inform and coordinate restriction with load dispatch center. Our grid code allow us to put the unit on load restriction in coordination with load dispatch center.

We thought FSR manual option might be best fit to meet our requirement in such special situation.

If you can suggest any alternative method to achieve safe unit load restrictions, such that unit shall not respond to any frequency excursion during such event.

I would appreciate if you could share with me the FSR manual operation procedure

best regards..........

This is becoming quite ... painful. The details come in dribs and drabs.

When Manual FSR control is used it only prevents the fuel control valve from increasing the fuel flow-rate. If something causes the fuel demand to decrease below the Manual FSR "gag" (setpoint), then the fuel will decrease.

When grid frequency decreases, EVERY SINGLE GENERATOR AND ITS PRIME MOVER SYNCHRONIZED TOGETHER ON THE SAME GRID WILL CHANGE SPEED. FULL STOP. PERIOD. No way to prevent that from ocurring. None. Zero. Zilch. Nada. Niente. Nope.

It's been my experience that in many parts of the world where grid frequency disturbances are common that the grid frequency tends to decrease and then cycle up and down. Many times the grid frequency increases above the rated grid frequency, and often it drops well below rated grid frequency.

Let's say the unit was operating at 75% of rated load (Part Load), and had a L.O. Cooler problem. And, let's say the unit was not on Pre-Selected Load Control but was stable at 75% of rated load (which it should be if the grid frequency were stable). Now, let's say the Operations Department, in conjunction with the Maintenance Department, decided the load should be reduced to 40% of rate load while the issue with the L.O. Cooler was being resolved. And, let's say the decision (a poor one) was made to use Manual FSR control to limit FSR to reduce fuel flow to reduce load to approximately 40% of rated load. So, the Manual FSR Control setpoint was reduced in steps until the load reached approximately 40% and the managers were all happy and work on the L.O. Cooler issue could begin.

Now, let's say that shortly after the load reduction and work on the L.O. Cooler had begun, and the grid "decided" to become unstable. A sizable drop in frequency, let's say 0.2 Hz occurred for a short period (approximately 20 seconds or so), and then the grid frequency began to oscillate--increasing then decreasing, in a somewhat periodic fashion (if plotted it might look like a sine waveform, or maybe a saw-tooth waveform), and the magnitudes of the "peaks and valleys" of the oscillations started to get a little worse, and the grid frequency actually went above rated regularly--not much, just by 0.1 Hz or so, but it still exceeded rated, which the bottoms of the negative dips went to about 0.3 Hz. And, the oscillations were now occurring much more randomly, so the waveforms were not very uniform-looking.

EVERY GENERATOR (AND ITS PRIME MOVER) SYNCHRONIZED TO THAT GRID AT THAT TIME IS GOING TO BE EXPERIENCING THE SAME CHANGES IN FREQUENCY. The units which are NOT at Base Load (are operating at Part Load, on Droop Speed Control) will be experiencing both changes in frequency AND changes in load. As the frequency goes down, the load will increase, and as the frequency goes up the load will decrease.

The unit which has been "restricted" using Manual FSR control will ALSO be experiencing frequency deviations--of the same magnitude and period as the other machine. The difference will be that instead of load increasing when the frequency decreases the load will basically remain the same, BUT when the frequency increases above rated the power output of the unit restricted by Manual FSR control will decrease. And this will occur every time the grid frequency increases above rated for as long as the grid frequency is unstable and oscillating, or even if the grid frequency is just higher than normal and not oscillating very much (it does happen, but not very often in most areas of the world prone to grid frequency problems).

So, you're saying to yourself now, "We don't care if the load decreases a little or a lot; we just don't want it go increase above our artificial limit." Manual FSR might be okay--for this purpose. Though it's not the intended purpose.

As for a procedure, I don't recognize the snippet you posted. I think you input an FSR setpoint (difficult to say exactly what load corresponds to a particular FSR; it's different for every unit), and the select "MANUAL FSR." What should happen is two things: A Process Alarm to say MANUAL FSR is not at the maximum limit (FSKMAX). And, the FSR should start ramping down to the setpoint that was entered. If it was me, I would enter a Manual FSR setpoint that was 3- or 4 FSR greater than the current FSR and then enable MANUAL FSR, watching to see if it ramped down relatively slowly (instead of jumping down to the new value). That way, you would know, in the future, how fast it ramps down--if it ramps down. And, then once you know the behaviour you could know how much to lower the FSR to prevent a sudden decrease in FSR. Again, without knowing a LOT about how the fuel control valve LVDTs are calibrated (and/or the liquid fuel flow divider feedback is calibrated) it's impossible to say what FSR corresponds to what load for your particular unit. That will be a trial-and-error situation--you will have to make small adjustments to the Manual FSR setpoint to see the effect on load.

Again, this is not the intended purpose for Manual FSR control, but it might work for you if you understand the way it works. It WILL NOT maintain speed (frequency) in the event of a grid frequency disturbance (NOTHING can do that!!!) and it will not prevent grid frequency disturbances from reducing the load below the value for Manual FSR. But, if you want to prevent the load from increasing above some amount, this might suffice.

Hope this helps!