S
SURYA
Makster,
i have gone through the Trip logs and my analysis also matching with your analysis.
GT-1 is almost near to base load and both GT'S are running in droop mode.Demand after tripping of 3rd unit 4MW the additional demand which needs to be shared by other 2 GT's as they are in droop mode.
Both GT's are shared the load upon trip ,however as there is no frequency control mechanism so system frequency reduced and units ( droop mode) were trying to compensate this by increasing FSR.
Exhaust temperature raised due to frequency drop & FSR increase due to droop error. GT-1 is running near to base load so FSR temperature control hit and unit started unloading and in turn entire unit frequency start reducing further because GT2 also not able to maintain the required additional demand as this also hit the FSRT limit and therefore this disturbance went into closed loop so units are tripped on under frequency.
This will happen when additional demand due to other unit trip/unloading is not able to achieve other units and no frequency control .
i think usually external loads ( usually which are not important to process ) will cut off either from GRP or load dispatch control system in order to safe the plant.
i also observed that IGV was not opened immediately (4to 5sec delay) after load sharing from 60% in GT2 . look into this whether it is due to lag in logic or re- calibration required.
i have gone through the Trip logs and my analysis also matching with your analysis.
GT-1 is almost near to base load and both GT'S are running in droop mode.Demand after tripping of 3rd unit 4MW the additional demand which needs to be shared by other 2 GT's as they are in droop mode.
Both GT's are shared the load upon trip ,however as there is no frequency control mechanism so system frequency reduced and units ( droop mode) were trying to compensate this by increasing FSR.
Exhaust temperature raised due to frequency drop & FSR increase due to droop error. GT-1 is running near to base load so FSR temperature control hit and unit started unloading and in turn entire unit frequency start reducing further because GT2 also not able to maintain the required additional demand as this also hit the FSRT limit and therefore this disturbance went into closed loop so units are tripped on under frequency.
This will happen when additional demand due to other unit trip/unloading is not able to achieve other units and no frequency control .
i think usually external loads ( usually which are not important to process ) will cut off either from GRP or load dispatch control system in order to safe the plant.
i also observed that IGV was not opened immediately (4to 5sec delay) after load sharing from 60% in GT2 . look into this whether it is due to lag in logic or re- calibration required.