It is about the "standard droop speed control" and how it can be affected by the FPRG or a bad calibration of the gas valves...etc.
Compared to the CONSTANT SETTABLE DROOP SPEED/LOAD CONTROL, The STANDARD DROOP/SPEED CONTROL has "no FSR value feedback" in its regulation loop. This mode of governor control changes FSR in proportion to speed error (droop) directly under the following equation:
FSRN = FSKRN1 + FSKRN2(TNR - TNH)
where FSKRN1 is the Initially set full speed no load fuel reference as calculated, and FSKRN2 is the ratio of percent change in fuel flow reference to percent change in speed/load reference.
OK! at full speed no load TNR-TNH would be equal to 0. and the FSRN value would be equal to FSKRN1, initially caclulated by the OEM for a particular fuel flow rate. And this value is the opening command of the GCV, so for this particular fuel flow rate it depends on the fuel heating value! also of the P2 pressure refrence FPRG!
Lets have an example: suppose FSKRN1 = 30%, when the machine finishes its start-up sequence normally the TNH (HP shaft speed) would be equal to TNR(turbine speed reference). The FSRN = FSKRN1 = 30%, as the machine was firstly commissioned for sure at this stage everything would be stable, because the 30% value was enough to make the machine stable at FSNL 100% speed, for example with an FPRG (gas ration valve control pressure reference) = 13bar.
Lets suppose we have a problem with the P2 pressure either the FPRG constant value or the SRV valve or even the P2 transmitter. This problem causes the P2 pressure to be 10bar when the machine at FSNL. So when the machine reaches FSNL and FSRN = 30% > we won't be having enough energy to make it stable, and TNH would to tend to drop. When it drops, TNR-TNH would be higher than 0 which will make FSRN higher than 30% to reach the FSNL speed again. We will be having a non stable state of the machine fluctuating at FSNL
Myself I'm having a problem with this mode and how it is vulnerable to any misbehave from the gas valves or P2 transmitter, the P2 set point (FPRG), and even a problem with the fuel injectors because we do not have an FSR feedback value in the loop.
NOTE 1: This enquiry is the same for the base load GCV opening value, at base load. And if the droop value is 4%, so TNR-TNH = 4% and 4% * FSKRN2 + FSKRN1 = FSRN, so there is no FSR Feedback value in the loop, at any load point we will be having an particular opening command of the GCV NO MORE!
NOTE 2: i am comparing this regulation loop to all other load regulation loops for single or double shafts where the FSR feedback value is always present. So we will be adding a certain value the actual FSR until we reach the load reference. So the for a certain load point we won't be having a particular pre-calculated value of FSRN which will make the system control adapt the FSRN value to the present conditions and parameters.
example: load output = 100MW, FPR2 = 12bar, FSRN = 40 %
if the the P2 drops for whatever the reason we will be having - load output = 100MW, FPR2 = 9bar, FSRN = 60 %
So the control system rises the FSRN value to maintain the load output.
Compared to the CONSTANT SETTABLE DROOP SPEED/LOAD CONTROL, The STANDARD DROOP/SPEED CONTROL has "no FSR value feedback" in its regulation loop. This mode of governor control changes FSR in proportion to speed error (droop) directly under the following equation:
FSRN = FSKRN1 + FSKRN2(TNR - TNH)
where FSKRN1 is the Initially set full speed no load fuel reference as calculated, and FSKRN2 is the ratio of percent change in fuel flow reference to percent change in speed/load reference.
OK! at full speed no load TNR-TNH would be equal to 0. and the FSRN value would be equal to FSKRN1, initially caclulated by the OEM for a particular fuel flow rate. And this value is the opening command of the GCV, so for this particular fuel flow rate it depends on the fuel heating value! also of the P2 pressure refrence FPRG!
Lets have an example: suppose FSKRN1 = 30%, when the machine finishes its start-up sequence normally the TNH (HP shaft speed) would be equal to TNR(turbine speed reference). The FSRN = FSKRN1 = 30%, as the machine was firstly commissioned for sure at this stage everything would be stable, because the 30% value was enough to make the machine stable at FSNL 100% speed, for example with an FPRG (gas ration valve control pressure reference) = 13bar.
Lets suppose we have a problem with the P2 pressure either the FPRG constant value or the SRV valve or even the P2 transmitter. This problem causes the P2 pressure to be 10bar when the machine at FSNL. So when the machine reaches FSNL and FSRN = 30% > we won't be having enough energy to make it stable, and TNH would to tend to drop. When it drops, TNR-TNH would be higher than 0 which will make FSRN higher than 30% to reach the FSNL speed again. We will be having a non stable state of the machine fluctuating at FSNL
Myself I'm having a problem with this mode and how it is vulnerable to any misbehave from the gas valves or P2 transmitter, the P2 set point (FPRG), and even a problem with the fuel injectors because we do not have an FSR feedback value in the loop.
NOTE 1: This enquiry is the same for the base load GCV opening value, at base load. And if the droop value is 4%, so TNR-TNH = 4% and 4% * FSKRN2 + FSKRN1 = FSRN, so there is no FSR Feedback value in the loop, at any load point we will be having an particular opening command of the GCV NO MORE!
NOTE 2: i am comparing this regulation loop to all other load regulation loops for single or double shafts where the FSR feedback value is always present. So we will be adding a certain value the actual FSR until we reach the load reference. So the for a certain load point we won't be having a particular pre-calculated value of FSRN which will make the system control adapt the FSRN value to the present conditions and parameters.
example: load output = 100MW, FPR2 = 12bar, FSRN = 40 %
if the the P2 drops for whatever the reason we will be having - load output = 100MW, FPR2 = 9bar, FSRN = 60 %
So the control system rises the FSRN value to maintain the load output.