On a process plant having 8 GTG's. Exporting power to GRID a grid 100MW, plant load is 110 MW. Out of 8 two machines are running on droop mode rest are in ECS auto. My question is droop machines MVAr increase to 100% of machine running load i.e 25MW and 25MVAr this was reduced locally by a control system. This was happened never in 4 years. Kindly explain why this happen.
If I had a nickel (5 cents US; $0.05) for every time I've heard, "It's NEVER done THAT before! Why did it do THAT??!?!" I would be a very rich man, VERY rich. Obscenely rich.
Based on the information provided, it's impossible to try to even guess as to what might have happened. Was there some issue with the grid voltage, and/or frequency?
Was there some upset in the process plant (large motors/load suddenly tripping off, or all starting at once)?
We don't know what controls the VArs (power factor) across the tie with the utility--or who. It could be a local control (you mentioned "ECS"), or it could be the utility has some means of controlling voltage/VArs/pf. We don't know how the ECS works, or how it's programmed to work.
We don't know the units are connected to the bus that is connected to the utility.
There's just too many unknowns to be able to say anything at all.
Sorry; I wish the response could have been more helpful.