GT Control Fundamentals
Transcript of GT Control Fundamentals
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Training on GT Controls
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Introduction to Control Philosophy
A Gas Turbine Consists of
1. Starting means2. Auxiliaries3. Compressor4. Combustion System5. Turbine 6. Exhaust7. Load
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Introduction to Control Philosophy
Control systemCommunicates with the turbine toMeasure, adjust the parameters
The Main Inputs areAir & Fueland the Outputs areLoad & Exhaust Gases.
It also protects the turbine from abnormal operations
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Gas Turbine Controls
1. Basic Control Parameters of GT
2. Minimum Gate Concept of
Six Control Loop
• Start up
• Speed/Load
• Temperature
• Acceleration
• Manual
• Shut down
Main
Auxiliary
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Simplified control schematic
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Example of Minimum FSR of Six Control Loops on HMI Screen
Min Value
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Detailed Control Schematic
We will use this as referenceas we go in detail of the course
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Startup Control
Start up control controls the amount of fuel to the GT from zero speed to Full Speed No Load
FSRSU is minimum of the six control loops
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Speed control schematic
• The Speed Control Loop ensures the correct speed as required by the system
• The Load Control Loop maintains the power out put. (The load control can be either Isochronous or Droop, depending on whether the system is connected to Grid or Isolated)
This serves both Speed & Load functions and so called Speed/Load Controller
FSRN is the minimum of Six Control Loops
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Speed Control Characteristics
Droop speed control is a proportional control,changing FSR in proportion to the difference betweenactual turbine speed and the speed reference (TNH & TNR)
Isochronous Controller is a closed loop controller that maintains the Turbine Speed to the reference speed by regulating FSR during the isolated operation.
Droop Control Curve
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Exhaust Temperature control
Temperature Controller ensures that the Turbine internals are protected from over heat and Optimum power is produced.
The firing temperature is difficult tomeasure and hence the Controller uses the exhaust thermocouplesas reference which is directly proportional to Firing Temperature
Tf = Tx (Pcd/Pa)k
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Exhaust/Firing Temperature Relation
The firing temperature remains constant even with increase in MW, FSR & CPR ratio with less exhaust temperatures
Curve comparing the load
at different ambient
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Temperature control scheme
FSRT is the minimum of the Six Control Loops
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Exhaust Temp. control set points
Exhaust temp control reference set point TTRXB calculated based on CPD
The back up exhaust temp reference is based on FSR in case of CPD measurement failure
TTKn_C
TTKn_I
FSR BIAS
CPD BIAS
TTKn_STTKn_M
TTKn_KIsothermal
Exh
aust
Tem
per
atu
reCPD FSR
Protection of Turbine internals and optimum power
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Acceleration control
Acceleration Control functions during sudden Load Changes and Start Up
TNH
0.35 %/sec
100%0%
0.10 %/sec
40% 50% 75% 95%
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Manual control
Manual Control Loop Can be used to limit fuel to prevent over firing and over riding active control
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Shut Down control
Shut down control loop reduces the fuel at a predetermined during shut down to reduce thermal stresses
FSRSD is the minimum of Six Control Loops
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IGV Control
IGV Control Loop
• Controls air fuel ratio
• Prevents Compressor
Pulsations
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IGV Control
Maintains higher Exhaust Temperature at partial loadsfor Combined Cycle Operation
IGV Schedule
IGV scheduling is requiredto ensure the protection fromPulsation/Stall by excessive opening at lower speeds/loads and negative pressures at partial loads by less opening
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IGV Control
Maintains higher Exhaust Temperature at partial loads for Combined Cycle Operation
IGV control reference
The exhaust temp. variesfor simple and combined cycle operations.IGV temperature control neverexceeds the base temperature control set point
Exh
aust
Tem
per
atu
reCPD
Isothermal
CPD BIASCPD BIASCPD BIAS
Base temp control set point
CC IGV temp control set point
SC control set point
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Electro Hydraulic Servo valve
Servo valve is the interface between the electrical and mechanical systems
Servo valve controls the direction and rate of motion of a hydraulic actuator based on the input current to the servo.
Servo valve contains three electrically isolated coils on the torque motor.
A null-bias spring positions the servo so that actuator goes to the fail safe position when ALL power and/or control signal is lost.
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Liquid Fuel Control Scheme
As the speed sensors in the FD send a signal to controller, it compares with demand signal and an error signal is created.
The amplifier in the controller will change the signal to drive the servo Valve of the Bypass valve.
Amplifier
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Liquid Fuel Control
The VSVO card receives the PR signals from 77FD – 1,2 &3 and Outputs Analog Signal, the fuel necessary to meet the demand.
The VSVO Card modulates Servo Valve based on FQROUT & FQ1
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Gas Fuel Control Scheme
Fuel Gas Control System consists of Stop ratio Valve, Gas Control Valve Controls
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Gas Stop Ratio Valve Scheme
• SRV is a dual function Valve, as a stop Valve and to hold desired P2 Pressure
• Control loop consists of both Pressure and Position Control Loops
• P2 is Controlled by pressure loop as a function of TNH with a gain & offset, the signal FPRG
• Position Loop takes feed back from Valve Position FSGR
The VSVO Card modulates Servo Valve based on FPRG, FPG & FSGR
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Gas Control Valve Scheme
The position of the gas control valve is proportional to FSR2 which represents called for gas fuel flow
The VSVO Card modulates Servo Valve based on FSROUT & FSG
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Fuel Splitter Scheme
• Transfer from one fuel to the other on command.
• Allow time for filling the lines with the type of fuel to which turbine operation is being transferred.
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IGV Control scheme
The Inlet Guide Vanes (IGVs) modulate during
• Acceleration of the gas turbine to rated speed • Loading and unloading • Deceleration of the gas turbine
The VSVO Card modulates Servo Valve based on CSRGV & CSGV
VSVO
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IGV Schedule
IGV modulation maintains
• Proper flows and pressures, and thus stresses, in the compressor• Maintains a minimum pressure drop across the fuel nozzles• High exhaust temperatures at low loads during combined cycle operation
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GT Protections
• GT is not allowed to start until permissives are set correctly
• GT Trips during operation if operating limits exceeded
Protection System ensures that GT is safe from dangerous operating conditions
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Duel Fuel Trip oil scheme
• The Trip Oil System is the primary interference between the master protection circuits and the fuel flow and VIGV position control devices