Actual IGV angle not same as both reference and feedback.

Dear everyone,

Our Gas Turbine, frame 6b with Mark VI control was shutdown normally 2 days ago.

Mechanical requested we open the IGV to carry out maintenance work.

The IGV was opened and was okay, but when we closed it after their inspection, the physical angle was more than the reference and the feedback, kindly assist.

Reference Feedback Actual
34 33.6 43
56 55.6 63
87 86.4 out of range.

88Hq and 88Qa were Power down but the physical igv is still 43degree.

I have read some thread on IGV but could not get what I wanted.

Thank you great people if thus forum, waiting patients for the solution.
Dayo, calibration of the feedback of the IGV's requires using a protractor to measure the actual angle of the blades, and a person who knows how to read a protractor and properly align it to the IGV blade. Its not something I can explain here.

Refer to your GE O+M manuals to understand that there are several different limits for the IGV and its associated hardware. There is a "hard" stop for minimum and maximum angle where the IGV ring stops hard on the case of compressor inlet casing. Secondly there is a maximum travel of the IGV hydraulic actuator that should bottom out before the IGV ring contacts the case for min and max. Adjustment of the "Dogbone" during commissioning sets these limits.

Typically the IGV regulator is put in manual and commanded to a value of zero%. This should force the IGV servo to port oil to actuator and close the IGV's until the hydraulic actuator reaches its closed limit. The IGV angle should be measured. Then in manual command the IGV's to 100% and measure the actual angle of the IGV blades. Understand that when commanded to zero, that the IGV actuator won't reach zero, but some value around ~32 deg, and same for 100% it should read something like ~87 deg angle. These actual minimum and maximum measured values are what should be in the regulator settings for MinPos and MaxPos.

In your case here I ask who was doing the measuring?
Have they done this before? If not who did it before and did they know what they were doing?
For the IGV feedback to have an error of more than 10 deg angle means to me:
The person who did the original calibration did something wrong.
The person reading the protractor does not know how to read it properly.
Something mechanically changed with the actuator/dogbone/IGV ring.
I do appreciate,

"""In your case here I ask who was doing the measuring?---
Have they done this before? ----If not who did it before and did they know what they were doing?"""

The IGV was commissioned 16years ago and has been operating fine (though we have rectified so many faults since then) but We have never experienced a situation where IGV physical is 43 degrees and both the reference and feedback are on 34 degrees and 33.6 degrees respectively.

In our case, feedback corresponds with reference but feedback did not corresponds with physical ( about 10 degrees difference).

When closing the IGV after physical inspection, no work was done yet, just physical inspection the igv moved from 86 degrees to 33 degrees and went up to 43 and did not go below that. That was when it was re- stroked and we got the values in the initial post sent.
Reference ----34 Feedback--- 33.6 Actual,‐------' 43

Feedback ----55.6
Physical--- ---'----63

Physical--------out of range.

Hydraulic oil and Lube Oil were powered off and IGV physical is still on 43 degrees.

""""For the IGV feedback to have an error of more than 10 deg angle means to me:
Something mechanically changed with the actuator/dogbone/IGV ring.""""

How can this physical difference be corrected? What and what should be done.

Thank you so much for your time and still waiting patiently.
Dayo, I would suggest that the system needs to be inspected. Something mechanically seems to have changed that needs to be inspected. It is possible that the "Dogbone" as it is called, the turnbuckle that links the IGV actuator to the IGV ring, has moved or its adjustment has changed. Without being onsite it is difficult to make specific recommendations. Can you provide pictures of the IGV actuator, IGV dogbone link, IGV position inidicator?

You are right.
The problem was actually the IGV position indicator.

It was discovered that the IGV lock pin was not in it position and both the washer and bolt that were holding the pointer in position were also worn out which probably led to a shift in igv position indicator (the pointer) and got stucked at 43degrees when IGV is actually in closed position (34 degrees I.e minimum IGV opening).

Pic. 1: IGV stroking values before and after adjustments
Pic 2: IGV Position pointer before adjustment
Pic 3: IGV Position pointer after adjustment

Thank you so much for your time.


Dayo, thank you for the feedback and glad you were able to find the issue. I will recommend that whenever the IGV angle is being checked it is best to do so in the inlet using a protractor to verify the actual angle of the IGV's. The pointer is a great indicator for general angle, but I would not trust that for an actual calibration verification. But glad it was just a pointer issue. Hopefully this helps someone in the future and you are smarter than yesterday.