IGV / Gas Control Valve Issue


Thread Starter

Dan Griffin


Operating a frame 7EA with the Mark IV control system. While loading the unit, the <S> processor indicates several diagnostic alarms once the IGV angle increases beyond the 57 degree position. The diagnostic alarms are voting mismatch <S>, CSRGV, FSRN, FSRN, FSROUT, FSRACC, FSRS1, FSR2. The LVDT feedback position and voltages look good across all 3 processors, but the reference CSRGV and FSR2 are affected by the issue that is being experienced.

When selecting temperature control off at or near base load, all diagnostic alarms will eventually clear, but once reselected, the list of diagnostics reoccurs and the same conditions exist.

With <R> and <T> controllers indicate the IGV's in temp control and are approximately 77 degrees(CSRGV) and FSR2 indicates 66%, the <S> indicates 84.0 degrees for CSRGV and the GCV reference FSR2 indicates 0.5%.

Looking for any troubleshooting advice.
<b>From the information provided</b> (and I'm not exactly clear on the whole problem/sequence of events here), it would appear that <S> is calculating a completely different IGV reference position (CSRGV, Control Stroke-Reference, Guide Vane). From what you're saying, it appears the IGV LVDT feedback for <S> is fine (we don't know if <S> is reading one of the LVDTs or the high-selected value of the two; that is shown on the Speedtronic elementary, presuming the hardware ("Berg") jumpers are shown in the actual positions).

Are there other Diagnostic Alarms that are active before the ones you listed are annunciated?

Does the unit have an HRSG on the exhaust? Is that why you are using IGV Temperature Control?

What is the reason for switching IGV Temp Control on and off--just for troubleshooting purposes?

The last thing to know about "IGV Temp Control" messages on GE-design heavy duty gas turbines is that even when IGV Temp Control <b>is NOT</b> enabled and active that when TTXM reaches a certain value (sorry; I can't remember if it's 700 Deg F or 900 Deg F) the IGVs are modulated by the Mark IV to maintain that temperature until they are fully open as the machine is loaded, and the display will indicate "IGV Temp Control" during this time. This is done to reduce combustion pulsations during loading, and is done automatically by the Mark IV even if operator-selected IGV Temp Control is not selected and active. (Isn't GE wonderful some times?)

So, it's not clear if you are operating the unit with IGV Temp Control Active at lower loads to maximize exhaust temperature, or if you are seeing the effects of maintaining exhaust temp during normal loading with operator-selected "IGV Temp Control" inactive.

You will need to find the algorithm in the Mark IV Speedtronic elementary that writes to CSRGV and then work backwards from there to find which of the various references is the least (CSRGV is the output of a MIN SELECT function with several inputs) in <S> and that will help you determine what the root cause of the problem is.

Please write back to let us know what you find or if you need more assistance.

Thanks for your response. I wanted to share what was found after further troubleshooting. I set up the Data page 16 with a list of points that are associated with the algorithm involving CSRGV. Upon review of the data with the turbine online with IGV temp control selected on, TTXM for the <S> processor was found to be 20 degrees F greater than the TTRX (Temp control reference). I then looked at the 18 exhaust thermocouples and determined which ones were associated with each of the 3 processors. It was found that 4 out of the 6 TC's for the <S> processor had abnormally higher readings. The turbine has recently returned to service after a major overhaul and elevated exhaust spreads have been noted since the overhaul. The turbine is scheduled to have a new set of fuel nozzles installed this weekend to correct the exhaust spread issue. I will post an update when the turbine is returned back to service.

Thanks again.
Dan Griffin,

Thanks for the feedback. This is one of the few "faults" of the Mark IV. In the first implementation of TMR each processor had dedicated exhaust thermocouples and did not know what the other processors believed the average exhaust temperature was. (This was solved in the Mark V and later Speedtronic control systems.) The <C> processor is where the exhaust temperature spread (from all the exhaust T/Cs) is accomplished, and in later versions of Mark IV there was some "convergence" of the TTXM value done through <C>, if I recall correctly.

Please let us know how things progress.