The start–up control operates as an open loop control using preset levels of the fuel command signal FSR. The levels are: “ZERO”, “FIRE”, “WARM–UP”, “ACCELERATE” and “MAX”. The Control Specifications provide proper settings calculated for the fuel anticipated at the site. The FSR levels are set as Control Constants in the SPEEDTRONIC Mark VI start–up control. Start–up control FSR signals operate through the minimum value gate to ensure that other control functions can limit FSR as required.
The fuel command signals are generated by the SPEEDTRONIC control start–up software. In addition to the three active start–up levels, the software sets maximum and minimum FSR and provides for manual control of FSR. Clicking on the targets for “MAN FSR CONTROL” and “FSR GAG RAISE OR LOWER” allows manual adjustment of FSR setting between FSRMIN and FSRMAX.
While the turbine is at rest, electronic checks are made of the fuel system stop and control valves, the accessories, and the voltage supplies. At this time, “SHUTDOWN STATUS” will be displayed on the <HMI>. Activating the Master Operation Switch (L43) from “OFF” to an operating mode will activate the ready circuit. If all protective circuits and trip latches are reset, the “STARTUP STATUS” and “READY TO START” messages will be displayed, indicating that the turbine will accept a start signal. Clicking on the “START” Master Control Switch (L1S) and “EXECUTE” will introduce the start signal to the logic sequence.
The start signal energizes the Master Control and Protection circuit (the “L4” circuit) and starts the necessary auxiliary equipment. The “L4” circuit permits pressurization of the trip oil system. With the “L4” circuit permissive and starting clutch automatically engaged, the starting device starts turning. Startup status message “STARTING” will be displayed on the <HMI>. See point “A” on the Typical Start–up Curve Figure (5.4). The starting clutch is a positive tooth type overrunning clutch which is self–engaging in the breakaway mode and overruns whenever the turbine rotor exceeds the turning gear speed.
When the turbine „breaks away‟ the turning gear will rotate the turbine rotor from 5 to 7 rpm. As the static starter begins its sequence, and accelerates the rotor the starting clutch will automatically disengage the turning gear from the turbine rotor. The turbine speed relay L14HM indicates that the turbine is turning at the speed required for proper purging and ignition in the combustors. Gas fired units that have exhaust configurations which can trap gas leakage (i.e., boilers) have a purge timer, L2TV, which is initiated with the L14HM signal.
The purge time is set to allow three to four changes of air through the unit to ensure that any combustible mixture has been purged from the system. The starting means will hold speed until L2TV has completed its cycle. Units which do not have extensive exhaust systems may not have a purge timer, but rely on the starting cycle and natural draft to purge the system.
The L14HM signal or completion of the purge cycle (L2TVX) „enables‟ fuel flow, ignition, sets firing level FSR, and initiates the firing timer L2F. See point “B” on Figure (5.4). When the flame detector output signals indicate flame has been established in the combustors (L28FD), the warm–up timer L2W starts and the fuel command signal is reduced to the “WARM–UP” FSR level. The warm–up time is provided to minimize the thermal stresses of the hot gas path parts during the initial part of the start–up.
If flame is not established by the time the L2F timer times out, typically 60 seconds, fuel flow is halted. The unit can be given another start signal, but firing will be delayed by the L2TV timer to avoid fuel accumulation in successive attempts. This sequence occurs even on units not requiring initial L2TV purge. At the completion of the warm–up period (L2WX), the start–up control ramps FSR at a predetermined rate to the setting for “ACCELERATE LIMIT”. The start–up cycle has been designed to moderate the highest firing temperature produced during acceleration. This is done by programming a slow rise in FSR. See point “C” on Figure (5.4).
As fuel is increased, the turbine begins the acceleration phase of start–up. The clutch is held in as long as the turning gear provides torque to the gas turbine. When the turbine overruns the turning gear, the clutch will disengage, shutting down the turning gear. Speed relay L14HA indicates the turbine is accelerating.
start–up phase ends when the unit attains full–speed–no–load (see point “D” on Figure (5.4). FSR is then controlled by the speed loop and the auxiliary systems are automatically shut down. The start–up control software establishes the maximum allowable levels of FSR signals during start–up. As stated before, other control circuits are able to reduce and modulate FSR to perform their control functions. In the acceleration phase of the start–up, FSR control usually passes to acceleration control, which monitors the rate of rotor acceleration. It is possible, but not normal, to reach the temperature control limit. The <HMI> display will show which parameter is limiting or controlling FSR.
The fuel command signals are generated by the SPEEDTRONIC control start–up software. In addition to the three active start–up levels, the software sets maximum and minimum FSR and provides for manual control of FSR. Clicking on the targets for “MAN FSR CONTROL” and “FSR GAG RAISE OR LOWER” allows manual adjustment of FSR setting between FSRMIN and FSRMAX.
While the turbine is at rest, electronic checks are made of the fuel system stop and control valves, the accessories, and the voltage supplies. At this time, “SHUTDOWN STATUS” will be displayed on the <HMI>. Activating the Master Operation Switch (L43) from “OFF” to an operating mode will activate the ready circuit. If all protective circuits and trip latches are reset, the “STARTUP STATUS” and “READY TO START” messages will be displayed, indicating that the turbine will accept a start signal. Clicking on the “START” Master Control Switch (L1S) and “EXECUTE” will introduce the start signal to the logic sequence.
The start signal energizes the Master Control and Protection circuit (the “L4” circuit) and starts the necessary auxiliary equipment. The “L4” circuit permits pressurization of the trip oil system. With the “L4” circuit permissive and starting clutch automatically engaged, the starting device starts turning. Startup status message “STARTING” will be displayed on the <HMI>. See point “A” on the Typical Start–up Curve Figure (5.4). The starting clutch is a positive tooth type overrunning clutch which is self–engaging in the breakaway mode and overruns whenever the turbine rotor exceeds the turning gear speed.
When the turbine „breaks away‟ the turning gear will rotate the turbine rotor from 5 to 7 rpm. As the static starter begins its sequence, and accelerates the rotor the starting clutch will automatically disengage the turning gear from the turbine rotor. The turbine speed relay L14HM indicates that the turbine is turning at the speed required for proper purging and ignition in the combustors. Gas fired units that have exhaust configurations which can trap gas leakage (i.e., boilers) have a purge timer, L2TV, which is initiated with the L14HM signal.
The purge time is set to allow three to four changes of air through the unit to ensure that any combustible mixture has been purged from the system. The starting means will hold speed until L2TV has completed its cycle. Units which do not have extensive exhaust systems may not have a purge timer, but rely on the starting cycle and natural draft to purge the system.
The L14HM signal or completion of the purge cycle (L2TVX) „enables‟ fuel flow, ignition, sets firing level FSR, and initiates the firing timer L2F. See point “B” on Figure (5.4). When the flame detector output signals indicate flame has been established in the combustors (L28FD), the warm–up timer L2W starts and the fuel command signal is reduced to the “WARM–UP” FSR level. The warm–up time is provided to minimize the thermal stresses of the hot gas path parts during the initial part of the start–up.
If flame is not established by the time the L2F timer times out, typically 60 seconds, fuel flow is halted. The unit can be given another start signal, but firing will be delayed by the L2TV timer to avoid fuel accumulation in successive attempts. This sequence occurs even on units not requiring initial L2TV purge. At the completion of the warm–up period (L2WX), the start–up control ramps FSR at a predetermined rate to the setting for “ACCELERATE LIMIT”. The start–up cycle has been designed to moderate the highest firing temperature produced during acceleration. This is done by programming a slow rise in FSR. See point “C” on Figure (5.4).
As fuel is increased, the turbine begins the acceleration phase of start–up. The clutch is held in as long as the turning gear provides torque to the gas turbine. When the turbine overruns the turning gear, the clutch will disengage, shutting down the turning gear. Speed relay L14HA indicates the turbine is accelerating.
start–up phase ends when the unit attains full–speed–no–load (see point “D” on Figure (5.4). FSR is then controlled by the speed loop and the auxiliary systems are automatically shut down. The start–up control software establishes the maximum allowable levels of FSR signals during start–up. As stated before, other control circuits are able to reduce and modulate FSR to perform their control functions. In the acceleration phase of the start–up, FSR control usually passes to acceleration control, which monitors the rate of rotor acceleration. It is possible, but not normal, to reach the temperature control limit. The <HMI> display will show which parameter is limiting or controlling FSR.
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