Dear all.
Iam asking about the sequence of shutdown of a f5 or f6 GE units during accelaration like 3000 rpm . Is the unit continue in startup process until reach FSNL then return to shutdown procedure or it take shutdown after stop command directly . Or there is a time delay ?
And what is the different between fired fired shutdown and normal shutdown ?
Tkanks alot.

 

@enigmad,

Very confusing description of your requests for information.

During a START, the unit speed cannot be manually changed or interrupted by an operator until the unit reaches FSNL. Most Mark* turbine control systems on the majority of Frame 5 and Frame 6 GE-design heavy duty single-shaft gas turbines driving generators are in START mode until the generator breaker closes (either automatically or manually).

Once the generator breaker closes, the majority of machines are then operating in Droop Speed Control (or some method of "load-sharing Isochronous speed control for a very few machines) until the operator or some condition initiates an automatic STOP. Once the generator breaker opens as soon as the machine speed decreases below 94.5% speed the machine CANNOT be re-started, nor can the speed of the machine be controlled by an operator. Since most Frame 5 & Frame 6 machines have a jaw clutch between the starting means and the turbine shaft they must go to zero speed before the clutch can be re-engaged without damaging the jaw clutch teeth. (Many newer machines have a SSS clutch which will allow the machine to be restarted as the speed decreases below approximately 100 RPM or so.)

Shutdown and fired shutdown often refer to the same sequence of ramping down the fuel flow to decelerate the machine while maintaining flame in the combustors down to a "safe" point at which the fuel can be completely stopped, and then the machine coasts down to COOLDOWN ON mode.

Initiating a STOP (either manually from the operator interface or by the control system after detection of some serious condition that doesn't require tripping the machine (which is stopping the fuel flow while the machine is still burning fuel)) puts the machine in the STOP mode of operation. It is not in STOP at any other time. If an operator initiates a STOP command while the machine is producing power at rated speed (the generator breaker is closed), the STOP sequence starts reducing the turbine speed reference which will in turn cause the fuel to be reduced (even though the machine speed WILL NOT actually change when synchronized to a well-regulated electrical grid/system!) which will cause the load (MW) to decrease. On the majority of GE machines, the load will actually go negative (meaning the machine is drawing amperes from the grid it is synchronized to--called "reverse power") and after a short time of reverse power the generator breaker will be tripped (opened), at which point the machine goes on a preprogrammed ramp-down of fuel to decrease speed while maintaining flame in the combustors so as to reduce the thermal stress on the machine as it is being shut down (this is the "fired" part of "fired shutdown").

During a START, the machine is in START mode as it goes through the purge sequence and then firing and warming-up and then accelerating until the torque assist from the starting means is no longer required and the machine can accelerate solely based on increasing fuel flow-rate up to FSNL. It is still in START mode until the generator breaker closes--at which point it usually goes (actually remains in) Droop Speed Control as the machine is loaded until it reaches Base (or Peak) Load.

If a machine is operating at Base (or Peak) Load, meaning CPD- or CPR-biased exhaust temperature control, and an operator initiates a STOP from the operator interface, the Mark* begins decreasing the turbine speed reference--but because the machine is operating on CPD- or CPR-biased exhaust temperature control and NOT Droop Speed Control the load will not actually change until FSRN drops below FSRT (FSRN is Speed Control FSR, and FSRT is exhaust temperature control FSR--when the machine is operating on CPD- or CPR-biased exhaust temperature control FSRN is increased slightly above FSRT so that the two FSR control modes won't fight each other for control of the fuel, so it takes some time, sometimes a minute or so, before load actually starts decreasing as FSRN drops below FSRT).

Good questions--I hope I answered them. Difficult to do without pictures and graphs and drawings and pencil & paper, but the above is what I think you were asking about. If you need clarifications (there is a very big difference between needing clarification and doubt!!) we are here to try to provide clarifications.

Tchau.

 

@enigmad,

Very confusing description of your requests for information.

During a START, the unit speed cannot be manually changed or interrupted by an operator until the unit reaches FSNL. Most Mark* turbine control systems on the majority of Frame 5 and Frame 6 GE-design heavy duty single-shaft gas turbines driving generators are in START mode until the generator breaker closes (either automatically or manually).

Once the generator breaker closes, the majority of machines are then operating in Droop Speed Control (or some method of "load-sharing Isochronous speed control for a very few machines) until the operator or some condition initiates an automatic STOP. Once the generator breaker opens as soon as the machine speed decreases below 94.5% speed the machine CANNOT be re-started, nor can the speed of the machine be controlled by an operator. Since most Frame 5 & Frame 6 machines have a jaw clutch between the starting means and the turbine shaft they must go to zero speed before the clutch can be re-engaged without damaging the jaw clutch teeth. (Many newer machines have a SSS clutch which will allow the machine to be restarted as the speed decreases below approximately 100 RPM or so.)

Shutdown and fired shutdown often refer to the same sequence of ramping down the fuel flow to decelerate the machine while maintaining flame in the combustors down to a "safe" point at which the fuel can be completely stopped, and then the machine coasts down to COOLDOWN ON mode.

Initiating a STOP (either manually from the operator interface or by the control system after detection of some serious condition that doesn't require tripping the machine (which is stopping the fuel flow while the machine is still burning fuel)) puts the machine in the STOP mode of operation. It is not in STOP at any other time. If an operator initiates a STOP command while the machine is producing power at rated speed (the generator breaker is closed), the STOP sequence starts reducing the turbine speed reference which will in turn cause the fuel to be reduced (even though the machine speed WILL NOT actually change when synchronized to a well-regulated electrical grid/system!) which will cause the load (MW) to decrease. On the majority of GE machines, the load will actually go negative (meaning the machine is drawing amperes from the grid it is synchronized to--called "reverse power") and after a short time of reverse power the generator breaker will be tripped (opened), at which point the machine goes on a preprogrammed ramp-down of fuel to decrease speed while maintaining flame in the combustors so as to reduce the thermal stress on the machine as it is being shut down (this is the "fired" part of "fired shutdown").

During a START, the machine is in START mode as it goes through the purge sequence and then firing and warming-up and then accelerating until the torque assist from the starting means is no longer required and the machine can accelerate solely based on increasing fuel flow-rate up to FSNL. It is still in START mode until the generator breaker closes--at which point it usually goes (actually remains in) Droop Speed Control as the machine is loaded until it reaches Base (or Peak) Load.

If a machine is operating at Base (or Peak) Load, meaning CPD- or CPR-biased exhaust temperature control, and an operator initiates a STOP from the operator interface, the Mark* begins decreasing the turbine speed reference--but because the machine is operating on CPD- or CPR-biased exhaust temperature control and NOT Droop Speed Control the load will not actually change until FSRN drops below FSRT (FSRN is Speed Control FSR, and FSRT is exhaust temperature control FSR--when the machine is operating on CPD- or CPR-biased exhaust temperature control FSRN is increased slightly above FSRT so that the two FSR control modes won't fight each other for control of the fuel, so it takes some time, sometimes a minute or so, before load actually starts decreasing as FSRN drops below FSRT).

Good questions--I hope I answered them. Difficult to do without pictures and graphs and drawings and pencil & paper, but the above is what I think you were asking about. If you need clarifications (there is a very big difference between needing clarification and doubt!!) we are here to try to provide clarifications.

Tchau.

Dear .
My quastion was during the startup sequence and the speed reach 3000 rpm and for vibration increasing reason the operator push stop command , did the unit change its sequence to shutdown sequence ?
Or continue till it reaches FSNL ?