No; the OEM's control philosophy and general programming practice does NOT allow operators to open the IGVs above the calculated reference.
There is usually an IGV display on the HMI, and there is sometimes (not always) a couple of buttons/targets which will allow an operator to <i>decrease</i> IGV angle to something less than the calculated reference angle, but not to increase the IGV angle to something more than the calculated reference angle. This is to protect the axial compressor.
Many GE-design heavy duty gas turbines with conventional (diffusion flame) combustors (that is, units without DLN combustion systems) also have the ability to enable or disable IGV Exhaust Temperature Control via buttons/targets on the IGV display. Enabling IGV Exhaust Temperature Control causes the turbine control system to keep the IGVs closed as much as possible during Part Load operation (loads less than Base Load) in order to maximize exhaust temperature, which is helpful when producing steam with the gas turbine exhaust. Disabling IGV Exhaust Temperature Control causes the turbine control system to allow the IGVs to follow their normal "schedule" (programming) and this results in lower exhaust temperatures at Part Load.
If you could explain what you are trying to accomplish--and a little more about the machine at your site (combustion system; fuel; exhaust configuration; etc.) we might be able to provide some more information.
Hope this helps!
By the way, there is more than ten years' worth of GE-design turbine control system and heavy duty gas turbine-related topics and information available on control.com. If you're using the desktop PC version of control.com, the 'Search' field is cleverly hidden at the far right of the Menu bar at the top of every control.com webpage. If you're using the mobile version of control.com, you need to tap on 'Control.com' on the Menu bar at the top of the page and then tap on 'Search.'
Using the Search feature of control.com is probably not like using your preferred World Wide Web search engine. You should use the Search 'Help' the first couple of times you use 'Search' to get the best results. Welcome to control.com!
<b>Moderator's Note:</b> just putting +IVG in the search box will not get you much. You need to add more to it. Click on the <b>?</b> next to the search box to get correct syntax and ideas on how to format your search.