During shutdown because of inlet air temperature thermocouple failure (2 of 4), the gas turbine compressor went into surge accompanied with high exhaust temperatures (>800 c) and high bearing vibrations and loud bang. The turbine trips because of low compressor discharge. The surge protection pressure transmitters at the air inlet plenum gave no action.
Can any one explain?
How do you define a surge when the surge protection is not triggered? Our f class has 3 dp switches for the surge. Loosing the 2v4 will trigger the gt protection if i am not mistaken.
I am not familiar with H class GT, but maybe information below will help you.
As I remember, the surge protection on f and e classes GT is implemented in failsafe protection circuit (relay protection block - schloesser) and have a release condition - turbine speed is more than 42 Hz. Protection trips by 2v3 dp switches. It means, that during startup and shutdown, when speed less than 42 Hz surge protection is not working.
Also I think, that temperature failure is not the cause of surge. Why do you that inlet temperature thermocouple failure influence on surge? You could try to find out what happens with combustion chamber in this unstable mode of work. It's look like a humming, that have influence on increasing of bearings vibration. Could you show some trends from control system? How change the position of blow-off valves, IGV during the shutdown?