Ok, I wrote it before, and I will write again
(Load 7 MW, and temp 371, angle 58 IGV temp control)
(Load 7.1 MW, temp 313, angle 57)

 

Yes; MSGFLD3 says IGV TEMP CONTROL, but that’s a bit of bad programming. In Simple Cycle mode the IGVs are held closed until the exhaust temperature reaches 700 deg F (if I recall correctly), which is approximately 371 deg C, and then they are modulated to hold that temp as the machine is loaded until they are Full Open. It’s “IGV Temp Control”—sort of, and it’s done to reduce dynamic pressure pulsations in the combustors at Part Load. It’s sort-of IGV Temp Control, but it’s not being done to maximize steam production and steam temperature, it’s being done to protect hot gas path parts. Once the IGVs are Full Open as the unit is loaded further the exhaust will again increase.

You said one unit’s exhaust temperature was 371 deg F. That’s probably this sort-of IGV Temp Control. And the IGVs on that unit are probably open further than the IGVs on the unit with the lower exhaust temperature. BUT YOU JUST WON’T PROVIDE THE DATA TO CONFIRM THAT FOR SOME REASON.

Over and out.

 

In my personal opinion if BOTH machines are running at the conditions you only recently fully stated then one of them needs maintenance and sooner rather than later. Without knowing any other conditions it’s hard to believe that both machines would be producing 7-7.1 MW at such different exhaust temperatures. Dirty inlet air filters, dirty IGVs, dirty axial compressor, high exhaust duct back-pressure—these are some of the things which can cause low power output.

I believe we have covered the issue of IGV Temp Control for the Simple Cycle application at your site. It’s purpose is to prevent or reduce dynamic pressure pulsations in the combustors during a range of Part Load operation (unlike IGV Exhaust Temperature Control which is used to maximize exhaust temperature at low loads (Part Load) to improve steam temperature and steam production). If I recall correctly the IGV Temperature Control that’s active on the machines at your site tries to maintain 700 deg F (approximately 371 deg C)—and that seems to coincide with the machine that has the IGVs open to 58.95 DGA and a 371 deg C exhaust temperature.

However, without a LOT more detailed information about both machines (maintenance histories, STARTs, TRIPs, hours of fired operation, etc.) there’s nothing more we can offer.