All you need to knbow is in the application code that it is installed on this unit..

I got one which showing & describing clearly that block ...

Again check on the App code then you can come back here for better support...

You even dont describe what is the problem you facing with...

Cause of this fault can be that:
- GCV not following reference
-GCV position high error indication
-GCV failed to open.....

Any time!

You suffer from the same illness too many suffer from: That EVERY GE-design Frame nxxx heavy duty gas turbine is exactly like every other GE-design heavy duty gas turbine of the same Frame size. AND NOTHING COULD BE FURTHER FROM THE TRUTH.

We don't know what Frame size unit you are working on.

We don't know what version of Toolbox/ToolboxST is used on the unit at your site which is experiencing problems. We don't know if this is happening during starting, or loading, or unloading, or during combustion mode transfers--you haven't told us very much.

We NOW know what the problem might be--but you would have gotten a better answer sooner if you had told us what the issue(s) is(are).

We don't know if GCV4 is a hydraulically-actuated gas control valve or an electrically-actuated gas control valve--a VERY important distinction.

When the alarm text says "not following reference" it could mean a LOT of things. The GCVs (hydraulically-actuated) usually employ LVDTs (Linear Variable Differential Transducers) to provide position feedback to the Mark*. If the valve isn't moving to the reference position when commanded, then it's not following the reference. OR, if it's moving more than commanded to, then it's not following the reference.

There can be many reasons for hydraulically-operated GCVs not to move, including dirty oil and dirty hydraulic filters (there is usually a filter at the gas valve actuator which usually doesn't have a high differential pressure switch or even a d-p gauge) which usually doesn't get changed as regularly as it should. The electro-hydraulic servo-valve can also develop issues if the oil is not clean. On some units, GCV-4 isn't used regularly, and therefore doesn't get "exercised" as often as the other GCVs (I mention that because some wise arse at the site will always say, "Well--why didn't the OTHER GCVs have the same problems??!!??" (and if one has had the problem--especially because of poor quality oil--the others will to sooner rather than later).

Also, the hydraulic actuator (usually a single-acting piston) can also develop worn areas such that the valve doesn't move as it should, or the piston ring(s) can develop leaks. It can also be the case that the servo current polarity wasn't properly verified when the unit was commissioned (we don't know how old it is--because you haven't told us when the problem started), or when the servo was recently replaced. (Problems like this that start recently can often start after some maintenance was done that is not being considered as a possible cause for the "new" problem. Servo current polarity verification should be performed EVERY time a new or refurbished servo is installed and it rarely is. (By the way, it IS NOT necessary to "recalibrate" when a new or refurbished servo is installed--but it almost always is....)

Some of the newer GCVs being used on GE-design heavy duty gas turbines have no user-serviceable parts, and yet those parts can break (like the closing spring, or the valve stem seals can be scored, or the valve plug and/or seat can be damaged).
So, there can be many reasons for a GCV (or the IGVs) to not follow the reference.

And, only you can decide how to proceed troubleshooting the problem. ESPECIALLY if you don't want to share very much about the circumstances and background of the unit (age; version of Toolbox/ToolboxST software; when the problem is occurring; what has been done to troubleshoot the problem--and, most importantly, what the results were; etc.). All we can do is offer some of the possiblities based on the information provided. And since electrically-actuated gas control valves are relatively new, there's probably not much we can offer about them--and you haven't told us what kind of actuator is used on the valves which are having the problem(s).

Again, that's about as much as we can do for you.

It would be great if you would write back to let us know how the problem was resolved!

Best of luck, and blessed day!