when unit in online, igv angle wont pass 62; machine load is restricted. turbine was shut down and an igv filter and servo replaced, lvdt calibrated, and igv driven to full reference.

however when unit is restarted, igv unable to drive beyond 57 degrees. even though speedtronic reference is saturated at -52 on r, s and t core. any ideas as to what would change when unit is online that would prevent igv from driving to 86?

<b>Moderator's note:</b> this message had no punctuation or words capitalized. Punctuation is my best guess.

 

This thread on control.com had several reasonable ideas:

http://www.control.com/thread/1347524777#1349169156

 

<b>When did this problem begin?</b>

After a maintenance outage?

After a unit trip from load?

It would certainly seem that something is amiss with the actuator. If the IGVs can be "stroked" open and closed (to perform an LVDT calibration) when there is no air flow through the unit (when it's at rest and not spinning at rated speed), then it would seem that something is changing when air is flowing through the IGVs when the unit is at rated speed.

If this is an older Frame 6 with the IGV actuator at the 6 o'clock position under the bellmouth (in a very difficult position to get to), then it could be that the hold-down bolts for the stationary portion of the actuator are broken or worn. I have seen this and diagnosed this problem more than once (broken hold-down bolts; elongated bolt holes; etc.).

Another problem may be that one or more of the gears on one or more of the IGV "axles" is loose or broken? Have you physically gone into the inlet/bellmouth area and checked that all the IGVs are being held in the closed position (when they are supposed to be closed) and all of them move to the open position (when they are supposed to be open)? Have you tried moving every single IGV by hand to be sure they are not loose?

Again, I think you need to inspect the IGV actuator and hold-down bolts and make sure that nothing is preventing the actuator from moving when there is air flow through the inlet (when the unit is at rated speed). The fact that the servo current is at negative saturation says that the Speedtronic is trying to move the IGVs to the reference angle, but something is not allowing the physical movement.

Please write back to let us know what you find.

 

Andrew,

" turbine was shut down and an igv filter and servo replaced, lvdt calibrated,"

Since you can move IGV when it was not running. Then problem won't be with servo valve and servo line filter.

Have you measure IGV angle with protector? if yes are they matching with the display?

Please verify your calibration.

Take care
G.Rajesh

 

problem begun after load was lowered to minimum load.

we have since used an hydraulic jack to force the igv to the correct position and now waiting on an outage to further investigate what has caused the restriction.

regards

 

If the hydraulic is left in place to keep the IGVs open and the turbine trips and the IGVs can't close that could cause axial compressor damage.

Please write back to let us know what you ultimately find!

 

It seems to me that mechanical linkage issue as described by CSA Check each mechanical linkage/assembly. What was done during outage? It seems to me that no maintenance has been carried out on it.

Good luck.