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IGV Opening
IGV stuck in 56 degree position

Dear All;

This morning, we have faced to one issue regarding gas turbine frame 5, control system MARK VI.

The turbine is loaded with 15 MGWATT, and IGV stuck in 56 degree position, we have two alarms coming in alarms page.


I don't now the issue is with servo valve or LVDT or IGV mechanical Stuck.

Kindly, if any had already same issue, can share with me his experience.


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Looks like you are in big trouble here as you obviously have no idea how your system works. Do you have GE manuals?

You have 2 Alarms " IGV position Servo Fault" This means that there is a fault with the Servo. "IGV not Following" The IGVs are not following the Control Setpoint (probably because of a faulty servo).

You do need to read a bit and try to understand how your system operates then trouble-shoot, that's how you learn.

If you don't have documents, drop me an email to and I'll send you something.

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As per your alarms, I am suspecting issue could be with the servo valve. spool inside the valve may get stuck so CSGV is not following the CSRGV which is relating to the second alarm.

Usually, if the mode is in simple cycle, once TTXM reaches CSKGVSSR (usually 700 deg F) for frame 5, iGV opening command will be 84 DEG. take a plot of csgv, ttxm, csrgv, cagv. should change as per the difference of CSGV & CSRGV. check for any leak across the hydraulic oil leaks across the double acting piston cylinder.

CSVG is voted value of output of each PCAA packs.

Sorry, there is a correction. It's not CSVG.
CAVG is the o/p current from each packs. When there diff exist b/w CSVG, CSRGC, CAFV will change..

The value we are seeing in the toolbox is the voted values of all three packs.

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>Sorry, there is a correction. It's not CSVG.
>CAVG is the o/p current from each packs.

The original poster said the unit used a Mark VI turbine control system. Mark VI turbine control system do no use I/O Packs--Mark VIe turbine control system use I/O Packs. Mark VI would use VSVO I/O cards to provide the current to the TSVO terminal boards.

The signal name of the IGV servo output current value would likely still be CAGV, or, cagv.

The first alarm listed by the original poster likely indicates the Mark VI is trying to change the IGV position by putting out "excessive" servo current. That indicates the servo is not capable of getting sufficient hydraulic flow to the IGV actuator to move the IGVs. That might be because of a problem with the servo valve (which would most likely be caused by dirty oil), or a problem with the IGV actuator or a problem with the IGV control rack or a problem with one or more IGV bushings. All of these would be mechanical problems (with the exception of a servo unable to flow sufficient hydraulic fluid).

The second alarm is probably related to the failure of the IGVs to actually move to the required position. Which would occur if the servo was dirty, or the IGV actuator had a problem, or the IGV rack and/or bushings had a problem or problems.

Depending on the age of the GE-design Frame 5 heavy duty gas turbine, the IGV actuator may be mounted under the floor of the inlet duct, beneath the compressor bellmouth in a very difficult-to-access place. Again, depending on the age of the unit it is possible the IGV actuator has some very worn components, or the mounting bolts of the IGV actuator have become loose and/or broken. The Heim joints of the actuator may have lots of looseness, or the turnbuckle may have broken loose.

But, presuming the servo current polarity of the outputs to the IGV servo were verified and the currents are all working together to create the torque in the servo to try to direct hydraulic fluid to the actuator to move the IGVs,

First thing to do is check the Servo currents. That's going to tell you pretty well what is going on.