Gas Turbine Interview QuestionsDescription complète
PKM-GT
Group Tech
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Gas turbine control system
Control of gas turbine is done by Startup control Acceleration control Speed control Temperature control Shut down control Manual control
How to determine operating condition
The sensors ,( detected turbine speed, exhaust thermocouple ,compressor discharge pressure,and other parameter)are used to determine the operating condition of the gas turbine
Fuel stroke reference (FSR)
FSR is the command signal for fuel flow Control of gas turbine is done by the lowest FSR(FSR SU, FSR ACC ,FSRN, FSRT,FSR SD,FSR MAN) The lowest FSR value of the six control loop is allowed to fuel control system
Simplify control schematic
Control shem. block diagram
Start up/Shut down sequence and control
Start up function objective Bring the gas turbine from zero speed to full speed safely by providing proper fuel to established flame and accelerate the turbine safely
Minimize the low cycle fatigue of the hot gas parts during the sequence
Speed detector
Speed is the important parameter during start up because the sequence of start up is the relation of speed
Turbine speed is measured by magnetic pick up Speed detector sent signal to Mark V to convert electrical signal to be the turbine speed in percent or rpm.
Speed converter
Speed relay
The speed relay that are used to control the sequence of start up L14HR Zero speed L14HM Minimum speed L14HA Acceleration speed L14HS Full speed
0.06 %
L14HR Zero Speed
0.31% 18% 19%
L14HP Spare speed signal
95% 90%
L14HF At field flashing speed
18% 15%
L14HM Minimum Firing Speed
50% 46%
L14HA Accelerating speed
96.4% 94.8% 60% 50% 8.4% 3.2%
L14HS Min operating speed
L14HC Auxiliary Cranking Speed Relay
L14HT Cool down Slow Roll Start Speed Relay
Start up control
Operate as an open loop control using preset level of the fuel command signal FSR(Zero , Fire ,Warm up,Accelerate,) FSR level are set as control constant and calculation in the Mark V
17.5%
14.4% 30.6%
0.05%/s 5%/s
1 sec
Start up FSR
Start up curve
Fire shut down
Fire shut down is an improvement over the former fuel shut off at L14HS drop out by maintaining flame down to lower speed to reduction the strain develop on hot gas path part
100 % FSRMAX -- Max Fuel Reference L83SDSET-- Preset FSRSD to Existing FSR L83SDMIN-- Set FSRSD to FSRMIN
FSRSD -- Shut down FSR Signal %
FSR -- Fuel Stroke Reference % FSRMIN -- FSR: Minimum % FSKSDn -- Shutdown FSR Ramp n L83JSDn -- Set FSRSD Ramp Rate to FSK SDn L83SDL-- FSRSD Lower Logic
L83SDR -- FSRSD Raise Logic FSRMIN-- FSR: Minimum % FSKSDB -- Shutdown FSR Ramp Dead band 0.1%
L83 SDL will be logic true in the case of below - L60SDM logic false when FSRSD-FSRMIN >0.1 % - L83RB logic true when Flame out >1 sec or Flame ON but TNH <30% - One can out(L28CAN)
L83JSD2 to 5 logic GT. Trip
FSRSD-FSRMIN >0.1 %
Flame ON TNH<30%
1 Can off
Speed control
The speed control system control the speed and load of the gas turbine to maintain speed at 100% at any load Speed control software will change FSR in proportion to the difference between TNH(turbine speed)and TNR(speed ref.) Turbine drive generator operating speed range normally from 95%-107% Start up reference speed is 100.3%
Speed droop
Droop speed control is the proportional control changing the FSR in proportion to the difference between actual turbine speed and turbine speed reference as the equation below (TNR-TNH)x Droop gain+FSRNL =FSRN
Droop control algorithm 100 %
10.5 1sec
14.7 %
Droop control curve
Synchronizing control
TNR for synchronizing is 100.3% to keep the generator faster than the grid If frequency has varied enough the speed matching circuit adjust TNR to maintain turbine speed 0.2 to 0.4 % faster than the grid
Turbine speed reference TNR
Speed control schematic
Auto synch logic
Synch permissive logic System line voltage 109% 86.5% Generator volts 109% 86.5% Line Frequency 50.5Hz 49.5Hz
Generator frequency 50.5Hz 49.5Hz
Synch speed matching permissive
Auto synch permissive logic
Temperature control
The temperature control system will limit fuel flow to gas turbine to maintain internal operating temperature within gas turbine limitation of turbine hot gas path parts. Firing temperature is the temperature exists at first stage nozzle. This temperature must be limited by control system
Firing temperature
It is impractical to measure temperature direct to the combustion chamber or at the turbine inlet So, the control system control the exhaust temperature instead. Firing temperature as a function of fuel flow (FSR) FSR temp. control curve are used as back up to primary CPD. Bias temp.
Exhaust temperature control
18 Chromel alumel TC are installed at exhaust plenum to sent signal to Mark V Exhaust temperature control soft ware 1.Temperature control command 2.Temp control bias calculation 3.Temp reference selection
Temperature control FSR.
Exhaust temp control command
Is the temperature control command (TTRXB)compare the exhaust temperature control set point(TTXM).The soft ware program converts the temperature error to fuel stroke reference signal FSRT
Temperature control bias
Firing temperature limit by linearized function of exhaust temperature and CPD backed up by linearized function of exhaust temperature and FSR
Isothermal
Compressor discharge pressure(CPD)
Exhaust temperature (TX)
Exhaust temperature (TX)
Temperature control Bias Isothermal
Fuel stroke reference(FSR)
Temperature control bias
Temperature control bias
GT. Operate by FG. or FO. If CPD bias >FSR bias Alarm will show GT.Operate by heavy oil(monitor nozzle plugging) if FSR bias >CPD bias alarm will show
CPD & FSR bias temp control
Temperature reference select program
For temperature reference select,three digital input signal are decode (L83JTN) to select one set of constant i.e. Base load open cycle select Base load combined cycle select Peak load select
Temperature reference select program
Fuel control system
Fuel control system will change fuel flow to the combustion in response to the fuel stroke reference signal(FSR) FSR1 call for liquid fuel flow FSR2 call for gas fuel flow FSR =
FSR1 + FSR2
Liquid fuel control system
Liquid fuel bypass servo valve
Liquid fuel control system
When liquid fuel is selected and start. The control system will check L4 logic(1). At minimum speed L20FLX(FO. trip valve) and L20CF(fuel oil clutch) will energized. When GT. Firing FSRSU will go to control turbine through fuel splitter and liquid fuel flow command FQROUT will demand to fuel oil by pass valve to control liquid fuel flow to combustion chamber.
FSR1V1 Fuel splitter Mixed Fuel Operation Completely on Liquid Fuel
Completely on Gas Fuel Fuel change permissive
3.3 %SP/s
Fuel Split Transfer Rate
Fraction of Liquid Fuel
Fraction of Liq Fuel Set point Command Increase Liquid Fuel Increase Gas Fuel Fuel Stroke Reference Fuel Splitter Liquid Fuel Purge Level
Fuel Splitter Gas Fuel Purge Level
Liquid Fuel Stroke Ref from Fuel Splitter 0.5 %
Gas Fuel Stroke Ref from Fuel Splitter 0.5 %
Liq Fuel Flow Reference Angle %
Liquid Fuel Stroke Ref from Fuel Splitter %
Liquid fuel bypass valve servo command[65FP-1]
Turbine Speed % Liquid Fuel Stop Valve Control Signal Master protective signal Calibration position reference % Calib selection command pass code Flow divider mag pickup speed Excessive Liq Fuel Startup Liq Fuel Bypass Valve Flow Detection Trouble Set point Liq fuel bypass valve servo current 30 % 10 sec
Liquid Fuel Flow High (trip ) 8.5 %
3%
Liq Fuel Bypass Valve Flow Detected Trouble Alarm
LF. Byp. Vlv. Servo Current Trouble Alarm
Master reset ALM171:'LIQUID FUEL CONTROL FAULT'
System check from flow divider and servo valve
Excessive flow on start up (trip GT. If excessive flow exist during warm up period) L60FFLH LVDT. Position feed back Bypass valve is not fully open when stop valve is close Loss of flow divider feed back
Fuel gas control system
Fuel gas flow is controlled by the gas speed ratio stop valve (SRV) and Gas control valve (GCV) SRV is designed to maintain a predetermined pressure(P2)at the inlet of gas control valve as a function of gas turbine speed GCV plug is intended to be proportional to FSR2 for fuel gas flow
GVC & SRV control block diagram FSRSU FSRSD FSRT FSRN
Min sel
FSR
Fuel Splitter
FSR2
GCV. Command
FSROUT
Gas Servo Command
DC mA
Servo valve 96GC
FG. Flow Control
Servo valve 90SR
FG. Press Control
FSRMAN
SRV. SRV. FPRGOUT Servo ComCommand mand
DC mA
GCV. Schematic diagram
Gas control valve out put
Gas Fuel Stroke Ref from Fuel Splitter
Gas Fuel Stop Valve Open Master protective signal Calibration selection command pass code
Calibration position reference %
GCV servo command [65GC-1] %
SRV. Schematic Turbine Speed
Master protective Gas Ratio Valve Open
SRV. Out put signal Stop/Speed Ratio Valve Shutdown Command Set point
-40 psi
Gas Ratio Valve Control Press Ref (psi) Fuel Gas Press Ratio Control Gain 3.5146 psi/% Fuel Gas Press Ratio Control Offset
Gas Ratio Valve Control Press Ref psi
-17.88 psi
Stop/speed ratio valve servo command [90SR-1] psi
Fuel gas control and monitor alarm
Excessive fuel flow during start up Loss of LVDT feed back on SRV and GCV
Servo current to SRV. detected prior to permissive to open Servo current to GCV. detected prior to permissive to open Inter valve pressure low
Gas Fuel Stroke Ref from Fuel Splitter % Position fdbck gas controlvalve [96GC-1] %
Gas control valve not following reference 3% 3 sec
5%
Gas control valve not following reference trip
5 sec
Position fdbck gas controlvalve [96GC-1] %
Gas control valve servo current %
-5 %
Gas Control Valve Position Feedback Fault
5%
Gas Control Valve Open Trouble Alarm
37.5 %
Gas Control Valve Servo Current Fault
Gas Fuel Stop Valve Open
3 sec
COMMAND PB Master reset
ALM133:'GAS CONTROL VALVE SERVO TROUBLE'
Position fdbck srv [96SR-1] % 33.3 %
-6.67 %
6.67 %
Startup Gas Fuel Stroke High
Stop/Ratio Valve Position FeedbackTrouble Alarm Lo
Stop/Ratio Valve Open Trouble Alarm
Speed ratio valve
servo current % 15 %
Gas Ratio Valve Open
Stop/Ratio Valve Servo Current Trouble Alarm
Interstage fuel gas press xmitter [96FG-2A] psi -5 psi
ALM134:'GAS FUEL INTERVALVE PRESSURE TROUBLE'
2 sec
COMMAND PB Master reset
ALM132:'GAS RATIO VALVE POSITION SERVO TROUBLE'
Dual fuel control
Gas turbine are designed to operate by both FG & FO. The control has provide the following feature Transfer from one fuel to another Allow time for filling the line Mix fuel operation
operation of liquid fuel nozzle purge when operating totally on Gas fuel.
Fuel splitter schematic
Fuel transfer
Mix Fuel operation
Limit on the fuel mixture are required to ensure Proper combustion Liquid fuel distribution Liquid fuel flow velocity Combustion ratio
Fuel transfer limit (For GE.9E)
Transfer(select one fuel)prior to startup Do not transfer fuel below 30 MW. Do not operate mix below 30% rated gas flow or 60% gas at 30MW.(to avoid nozzle pressure ratio dropping below 1.25 and possibly causing combustion chamber pulsation.)
Fuel transfer limit (For GE.9E)
Do not mixed below 10% rated liquid flow(to avoid excessive liquid fuel recalculation flow resulting in fuel over heating and possibly causing fuel oil pump damage.)
Mix fuel Allowable range curve Rated
MW NO
LOAD
MIXED OK
MIXED
No MIX
30 MW NO MIXED
0 100
30 70
60 40
90 10
100 % GAS % LIQ 0
Modulate Inlet Guide Vane
Protect compressor pulsation by modulate during the acceleration of gas turbine to rated speed.
IGV modulation maintain proper flow and pressure to combustion. Maintain high exhaust temperature at low load when combined cycle application.
Modulate IGV control scheme.
IGV. Control control reference (CSRGV) L83GVMAX
CSRGV
86 DGA
CPD.
(IGV CONTROL REFERENCE) IGV part Speed
TNH.
MIN SEL
57 DGA MAX SEL
CLOSE OPEN
IGV MAN
L83GVMAN TTRX L83GVSS 371 c 1120 c TTXM
MIN SEL
IGV TEMP CON TROL
X
+
CSRGVX
IGV. Control Algorithm from Mark V Temp Control and Manual Control Ref Airflow Control Reference %
IGV on Temperature Control
1 DGA/%
Stator 17 IGV Gain VIGV Temp Control Airflow Ref Offset
0 DGA
IGV Manual Control Permissive 57 DGA 57 DGA
IGV at Minimum Position
Permissive Inlet Guide Vane Ref IGV Part speed control 86 DGA
VIGV. Reference Angle (DGA)
CPRS. OFF Line washing IGV at Maximum Position
Calibration position reference % Calibration selection command pass code
HP Turbine Speed % VIGV Part Speed HP Corr Speed Offset % VIGV Part Speed HP Corr Speed Gain Open IGV Position VIGV Part Speed Ref Min Setpoint
Turbine Speed HP, Iso Corrected 77.320 %
6.786 86 DGA
34 DGA
DGA/% Part Speed VIGV Reference
IGV. Control control reference (CSRGV) L83GVMAX
CSRGV
86 DGA
CPD.
(IGV CONTROL REFERENCE) IGV part Speed
TNH.
MIN SEL
57 DGA MAX SEL
CLOSE OPEN
IGV MAN
L83GVMAN TTRX L83GVSS 371 c 1120 c TTXM
MIN SEL
IGV TEMP CON TROL
X
+
CSRGVX
From Where ?
CSRGVX TTXM TTRX CSKGVDB
2 deg F
X Min SEL
L83GVDB TTRXGVB
X
700 F 2048 F
CSRGVX
L83GVSS
X
TNGV CSKGVTPG CSKGVTC CSRGV L83GVMAN_CMD
2 deg F 4 sec
X
X
T
V = OUT 1+TS V
RESET OUT =V
IGV MAN
TTRX L83REC TTRXC TTRXR1 1.5 F/sec TTRXR2
-1 F/sec
TTRMINSEL
MED SEL
TTRX
X
X Z-1
IGV Temperature control (CSRGVX) Bias by FSR. , CPD. +X
FSR
X
42.707 %
Conner
+
X
L60TRF A A
Slope4.987 F/% 1140 deg F
TTRMINSEL
MIN SEL
ISO thermal
CPD
+X
X
+
X
8.058 prs_R
Conner
27.342 F/ prs
Slope L83JTN
L83JTN = Temperature select logic(by damper&fuel) N = 0 Operate open cycle mode on Gas fuel N = 1 Operate Combined cycle mode on Gas fuel N = 2 Operate open cycle on mode Liquid fuel N = 3 Operate Combined cycle mode on Liquid fuel For example show value of curve N= 1
IGV. Operation curve
IGV. Fault detection Position feedback IGV [96TV-1]
TCQA-REG-CUR IGV control servo current
DGA 31 DGA
IGV - Loss of Feedback Alarm
35 DGA
IGV - Vanes Open Alarm
% -30 %
IGV Control Permissive 5 sec
COMMAND PB Master reset
IGV - Servo Current Alarm - Neg. Saturation
IGV. Not following CSRGV. Position feedback IGV [96TV-1] DGA VIGV Reference Angle DGA 7.5 DGA
