IGV temperature control

Dear All,

IGV temp. ctrl has been covered many times in this forum but I haven’t found the answer to a question that’s been running in my head for some time now.
We’ve got several 6FA at our plant. Electricity generation application, mainly at part load in a small grid. Exhaust to horizontal HRSG through a diverter damper for combined cycle operation or simple cycle operation. Liquid fuel, MNQ Combustors with water injection for NOx reduction and no IBH. 6FA.01 TMR Mark V and 6FA.03 TMR Mark VI.

All our units have command push buttons to switch IGV temperature control ON or OFF. After the units are started, we select IGV temperature ON or OFF depending on the configuration we are going to run the unit (combined cycle or simple cycle).

In our 6FA.01, IGV temperature control ON can only be switched on if the load is below 3.6 MW (or FSRT is in control) and IGV temperature control OFF can only be switched on if the load is below 9 MW (or the IGVs are fully open). When L4 falls, IGV temp. ctrl is latched to ON.
I ass-umed the reason for this small load window to change IGV temp. ctrl. mode was that when switching mode at higher loads (with the IGVs still regulating), IGVs would move quickly to their new position causing some type of combustion instability.

A few weeks ago, I noticed a difference between the CSP in our 6FA.01 and our 6FA.03. Whilst explaining IGV temp. ctrl. to a trainee in one of the 6FA.03 units, whilst on combined cycle mode, the OFF command push button was inadvertently pressed. The unit was at 15 MW and there was a mode change over. IGVs opened to their new reference (the IGVs moved from 58 DGA to 70 DGA). We pressed the ON command push button and the unit returned to its original configuration. No alarms where annunciated and the unit didn’t trip. Looking at the 6FA.03 CSP, we observed that there is no load permissive for switching modes as there is in the 6FA.01.

I’m trying to understand the reason why there is this difference between the control in our units and what could be the consequences (if any) of an IGV temp. ctrl. mode change over at a higher load.

Thanks a lot.
Just a philosophy change. No consequences; no potential damage. As machines get more "mature" (older) and the learning "curve" levels out, some of the initial worries cease to be worries.

It's just age. The age of the machines, in general.

And experience.

And a change in responsibility for the control schemes.

Nothing more and nothing less.

Probably. UNLESS there are major differences in the axial compressors and IGVs. Hardware-wise.
WOW. You are asking alot.

IGV control simply controls the mass air flow through the compressor.

I am not going into all of the details of IGV, machines with DLN, etc, etc. I do not even have the details of your plant to discuss.

I like to think of a cutting torch. Initially you set the torch to the perfect mixture of air and fuel to control the temp being exhausted to the HRSG.

IGV control OFF; you just pressed the O2 lever on your torch making a very hot flame.

The only real way to completely understand is READ those fine manuals that come with the machine. We call them the green books. Even since the MKI, the books have the info. Just can be hard to find.

Hopefully CSA will jump in a give those very detailed responses that I have come to enjoy.
CSA is trying desperately to give up this habit. (Seriously, folks.)

I just can't bear to see the kinds of lame responses that are being given to some of these threads.... Yes the documentation is the best place to start--but unfortunately GE documentation is also pretty lame at times, and takes some "reading between the lines."

And, I do have a fair amount of Mark V knowledge (gained through years of new unit start-ups and retrofits). So, I still kind of feel a little bit of responsiblity to respond to these questions that are Mark V-related.