Hello again.
Basically, I work at a petrochemical site which has two 25MW Hitachi H25 Gas Turbines (GT 1 & 2), one Alstom Tornado Gas Turbine of 4MW and a Steam Turbine (STG) of 15MW. We are not connected to any grid and we operate in island mode. GT-2 is normally running on Isoch mode maintaining system frequency at 50 Hz, while all other generators are on droop mode. However, it is to be noted that both GT-1 & GT-2 generators are of same capacity.
Before the event, all the generators were in service. GT-1 was running at 19.6MW, GT-2 at 21.6 MW (Iso), Tornado at 4MW and STG at 10MW. We initiated the shutdown of tornado turbine due to maintenance after creating margin in GT-2 and bringing it down to 17MW. However, due to some fault, Tornado tripped and suddenly there was an additional 4MW load on the system. Ideally, GT-2 should have taken the entire load and nothing should have happened, but what happened in reality was that both GT-1 and GT-2 took equal load i.e. 2MW each. GT-1 load went to 21.6MW, and it tripped on exhaust temperature. At that time IGVs were 78% open. GT-2 (Iso) went up to 19.6MW after which its speed started to decrease. Exhaust temperatures also began to rise and finally GT-2 generator breaker also tripped on under frequency. IGVs of GT-2 were only 68% open when it tripped. The load on GT-2 was 20.6MW at that instant. This resulted in site total power outage and an emergency situation. The tripping time of both GTs is virtually the same only separated by milliseconds with GT-1 believed to have tripped first. The time difference between Tornado tripping and both GTs tripping is 15 seconds.
In all this scenario, I am unable to understand following:
1) GT-2 was on Iso and running at 17MW. Why didn't it take the additional 4MW load entirely since it had enough margin?
2) Why didn't GT-2 IGVs respond on additional load and rise in exhaust temperature. During all this scenario, they only went from 62% to 68%?
3) Both GTs were running fine at 20MW and 21MW before respectively, but when sudden load came, both gave away. Why?
4) GT-1 tripped on exhaust temperature but tripping of GT-2 is very queer. There was enough margin in IGVs when frequency began to decrease which should have catered the additional load?
The event and alarm list can be found at the following link for additional info. Any sort of help would be greatly appreciated.
https://drive.google.com/open?id=1DLPulAapA7H06hfzZr-M2R6wxWbjFXSv
https://drive.google.com/open?id=1bqfD9wq8f1lSXE8h1ZciVpYEbbIC6DuW
Basically, I work at a petrochemical site which has two 25MW Hitachi H25 Gas Turbines (GT 1 & 2), one Alstom Tornado Gas Turbine of 4MW and a Steam Turbine (STG) of 15MW. We are not connected to any grid and we operate in island mode. GT-2 is normally running on Isoch mode maintaining system frequency at 50 Hz, while all other generators are on droop mode. However, it is to be noted that both GT-1 & GT-2 generators are of same capacity.
Before the event, all the generators were in service. GT-1 was running at 19.6MW, GT-2 at 21.6 MW (Iso), Tornado at 4MW and STG at 10MW. We initiated the shutdown of tornado turbine due to maintenance after creating margin in GT-2 and bringing it down to 17MW. However, due to some fault, Tornado tripped and suddenly there was an additional 4MW load on the system. Ideally, GT-2 should have taken the entire load and nothing should have happened, but what happened in reality was that both GT-1 and GT-2 took equal load i.e. 2MW each. GT-1 load went to 21.6MW, and it tripped on exhaust temperature. At that time IGVs were 78% open. GT-2 (Iso) went up to 19.6MW after which its speed started to decrease. Exhaust temperatures also began to rise and finally GT-2 generator breaker also tripped on under frequency. IGVs of GT-2 were only 68% open when it tripped. The load on GT-2 was 20.6MW at that instant. This resulted in site total power outage and an emergency situation. The tripping time of both GTs is virtually the same only separated by milliseconds with GT-1 believed to have tripped first. The time difference between Tornado tripping and both GTs tripping is 15 seconds.
In all this scenario, I am unable to understand following:
1) GT-2 was on Iso and running at 17MW. Why didn't it take the additional 4MW load entirely since it had enough margin?
2) Why didn't GT-2 IGVs respond on additional load and rise in exhaust temperature. During all this scenario, they only went from 62% to 68%?
3) Both GTs were running fine at 20MW and 21MW before respectively, but when sudden load came, both gave away. Why?
4) GT-1 tripped on exhaust temperature but tripping of GT-2 is very queer. There was enough margin in IGVs when frequency began to decrease which should have catered the additional load?
The event and alarm list can be found at the following link for additional info. Any sort of help would be greatly appreciated.
https://drive.google.com/open?id=1DLPulAapA7H06hfzZr-M2R6wxWbjFXSv
https://drive.google.com/open?id=1bqfD9wq8f1lSXE8h1ZciVpYEbbIC6DuW