Gas Turbine Control System1 - Nema

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Gas Turbine Control System

Speedtronic Mark IV

Kawas Gas Power ProjectNTPC Limited


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GAS TURBINE CONTROL SYSTEMS

Gas Station GT Control System

Auriya MIDAS 8000 (MHI)

Anta Procontrol-P (ABB)

Jhanor Procontrol-P (ABB)

Dadri Teleperm-ME (Siemens)

Faridabad Teleperm-XP (Siemens)

Kawas Mark-IV (GE)

Kayamkulam Mark- V (GE)


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CONTROL SYSTEM WORKS ?


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CONTROL SYSTEM FUNCTIONS

Monitoring (Supervisory) :Provides measurement of all the process parameters likePressure, position of valves , temp. , flow etc. It also providesalarms to the operator when required.

Control (CLCS) :Controls the process parameters to achieve the desiredoutput while keeping the equipments operating underdesigned limitations.

Interlock/ Sequencing/Protection (OLCS) :Ensures safe and automated start-up logic. All the equipments

do have certain limitations for operating parameters. If itcrosses the limits, the system should trip / stop to preventany damages.


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CONTROL SYSTEM SIGNALS

Information and commands are transmitted in form ofelectrical signals. There are two types of electrical signals

Analog signalsAnalog electrical signals have continuous values. They

convey process information within a defined range. Normalindustry standards are 4-20 mA current or voltage signals.These signals are employed in a CLCS.

They follow arithmetic algebra for calculation of results.

Logic SignalsLogic signal are discrete values normally a 0 or 1. In

electrical terms it can be attributed to presence or absence ofvoltage. These signals are employed in an OLCS. Booleanalgebra is applicable for logic signal.


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GT Instrumentation

Servo- valves (analog) and solenoids (logic)

Speed Sensors (analog)

LVDTs (analog) and Limit switches (logic)

Spark plug (logic) and flame detectors (logic)

Pressure transmitters (analog) and Pressure Switches(logic)

Actuators (analog and logic)

Thermocouples (analog) and temperature switches (logic)

Level switches (logic) Fire sensors (logic) and Leak detectors (logic)

Vibration sensors (logic)


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GT CONTROL SYSTEM AT KAWAS

Control system used for Gas Turbines at Kawas isSPEEDTRONICS MARK IV. This system was developed byM/s GE, USA in 1982.

The mark IV system is based on TMR control philosophy.INTEL 8086 & 80286 microprocessor based controllers( microcomputers ) perform calculations required for thecontrol , protection & sequencing of the gas turbine.

For governing of the turbine electro-hydraulic technologyis used.


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CONTROL PHILOSOPHY

The main concept behind three redundant (TMR)controllers is for two-third voting concept.

The design of each computer contains circuitry to achievefail safe condition.

On loss of power or when Trip condition occurs, itremoves power from the coil.


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SPEEDTRONIC HARDWARE

The SPEEDTRONIC panel comprises of following components.

Three redundant controllers < R >, < S >, & < T >.These controllers are exactly identical in hardware &software.

One communicator < C >.

Signal processing/conditioning I/O modules

Operator interface/Communication modules

Relays

Power distribution module and power supplies


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< R > < S > < T > CONTROLLERS

Perform sequencing of auxiliaries to allow fullyautomated startup, shutdown, and cool down.

Control of liquid, gas, or both fuels as per therequirements ofStart-up and shutdown conditions.Speed or load control under part-load conditions.Temperature control under base load conditions.

Inlet guide vanes and water injection control.

Turbine protection against adverse operating situations.


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C- COMMUNICATOR

Monitors the healthiness of the voting controllers< R >, < S > & < T > and initiates an audio visual alarmwhen there is disagreement between any controlparameter / logic signal in , & .

Provides User-interface like CRT, Printer & Inputcommands.

It contains diagnostic software, interface with logic andanalog input & provides RS 232 link for remote interface.


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LOGIC INPUTS

All the critical logic inputs from field are wired to ContactInput Module (CIM ) 1 or 2, where this signal is paralleledto the three optical isolators & fed to separate digital inputcards in the < R >, < S > & < T > controllers.Communicator < C > feed these informations to the CRT.

Logic i/p which are not critical, are fed to communicator< C > through CIM 3 to 6 after optical isolation.

Optical isolation : A semiconductor device consisting of

an LED & a phototransistor in close proximity. Currentthrough the LED causes an internal light emission thatforces current to flow in the phototransistor.


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LOGIC OUTPUTS

2 out of 3 ( 2/3 ) logic voting for output signal isperformed by Relay Driver Module (RDM).Here fail safelogic is implemented, means no power will result in safecondition.

Non voted logic outputs are available through .


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ANALOG INPUTS

In Gas turbine control system all the analog inputs like,LVDT, pressure, vibration etc are fed to analog input ,output modules, AIO 1,2 & 3.

For temperature measurement TCM modules are used.There is one module each for , & controllersand two modules for communicator < C >.


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ANALOG OUTPUTS

There are two types of analog outputs

DC milliamp current from controllers,, & toservo valves for functions such as liquid/gas fuel flow

control and IGV control. If any controller fail remainingtwo will be able to drive the servo valve.

4-20 mA and 0-10V DC analog outputs are also available.


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BRIEF DESCRIPTION OF HARDWARE

The cards used in Mark-IV Speedtronic control systemare as follows:

HAFA: 16 Analogue and 32 Digital input cards. HAIC: 16 analogue input and [OPM] interface. HCMC: RS232 interface HCVA: Analogue output card (2) HIOD: 32 Digital I/O Board HPRB: 4 pulse rate input, HMPK: Microprocessor Card.

HVDB: Video Driver Board, interface with CRT HXPD: CPU expander,PROM,16 digital I/O,8 interrupt NTCF: 14 thermocouple input per card NVCD: 6 vibration input per card


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BRIEF DESCRIPTION OF HARDWARE

HSAA: Servo-amplifier,2 LVDT/servo channel per card.It is a interface between turbine control system andhydraulic actuator that positions the valve.

Contact Input Module (CIM): 16 voting input connectedto R/S/T and 32 nonvoting input to C.

Analogue I/O module: It is used for remote analogueinterface and passive filtering

Thermocouple input module (TCM): TCM.R/S/T provides14 voting input to R/S/T. TCM.C1/C2/C3 gives 14nonvoting input to C.First input provides cold junction reference.


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FUEL STROKE REFERENCE (FSR)

FSRis a fuel demand signal calculated by the controlsystem to regulate the amount of fuel injection in theturbine. Independent FSR values are calculated for thefollowing controls.

1. Start up Control (FSRSU)2. Acceleration Control (FSRACC)3. Speed/Load Control (FSRN)4. Temperature Control (FSRT)

All these FSR values are compared and the minimum value ispassed to the fuel control valves.


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START - UP + ACCELERATION CONTROL

This is an open loopcontroller whichincreases the

FSR , as theturbine start-upsequence passesthroughpre- assigned statesof Firing, Warm-up

and acceleration.


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PART LOAD OPERATION

During part load Gas Turbine is controlled by Speed/Loadcontrol algorithm.

FSRN=(TNR-TNH)*Droop gain+ FSR FSNL

where

TNR- Speed Reference.Rate of change 0.4 or 0.8 % N/min

TNH- Actual SpeedFSNL FSR-14.5 %Droop Gain- 10.5 %/%N


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BASE LOAD OPERATION

At base load the turbine control shifts to temperature controlalgorithm where

FSRT (TTRX-TTXM)

Where

TTRX Exhaust Temperature Control Reference

TTXM Actual Exhaust Temperature


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EXHAUST TEMPERATURE REF. (TTRX) CALCULATION

593 593 593

585.752

578.202

570.652

563.102

555.552

548.002

540.452536.677

520

530

540

550560

570

580

590

600

5 6 7 8 9 10 11CPD

ExhaustTem

p.

Referenc

Isothermal Limit Exhaust Temp. Reference


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FUEL SPLITTER

FSR1 = FX1 * FSR (liquid fuel)

FSR2= [100 FX1] * FSR (Gas Fuel)

FX1= Fraction of Liquid Fuel [Range 0 100%]

FX1=0% Means Total Gas Fuel.

FX1=100% Means Total Liquid Fuel.

Rate of change of FX1 i.e. ramp rate = FXK1 =1.6%/Sec (1 Minute for fuel changeover)


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Auto Fuel Change-over conditions

UNIT RUNNING ON GAS FUEL

Gas pressure low (17.5 Bar BeforeStop Ratio Valve).

Transfer to HSD

VA 13-1,2 inter valve gas pressureHigh (>3 Bar, Time delay 40 Sec)

Transfer to HSD, if notS/D after 45 Sec.

UNIT RUNNING ON HSD

HSD tank level low (2.0 Meters). Transfer to NGL/ARN


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Auto Fuel Change-over conditions

UNIT RUNNING ON NAPHTHA FUEL

Naphtha fuel pressure low -


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Tripping vs Normal Shutdown

TrippingAs soon as a tripping condition is detected, L4 i.e MasterProtective logic signal gets dropped leading to immediateclosing of the fuel valves and hence fast deceleration of the

turbine.

Normal shutdownIn case of a normal shutdown order/condition, TNR (FSR)value decreases gradually to unload the unit till generatorbreaker opens at reverse power.

FSR decreases further as per FSRMIN and fuel is totally cut offat the blow-out speed of 35%.


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INLET GUIDE VANE

The guide vanes are installed at inlet to the compressor.They are used to direct and control the air flow to the firststage of the axial flow compressor.

Variable compressor inlet guide vanes provide protectionagainst compressor pulsation during turbine start - up andshut down.

It facilitates proper exhaust temperature for combined cycleoperation during partial loading of Gas Turbine.

This variable inlet guide vane actuator is an hydraulicallyactuated assembly having a closed feed back control loop , tocontrol the guide vanes angle.


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IGV TEMPERATURE CONTROL

Variable compressor Inlet Guide Vanes modulate to maintainhigh exhaust temperature during part load for combinedcycle operation.

Initially during normal start-up the IGV is full closed, i.e.

34 Deg. as proper temp corrected speed is reached IGV willopen to a preset value, i.e.54 DEG, mini & remain at thisposition, until exhaust temp. condition asks for more opening

If IGV temperature control is OFF, it starts opening from54 deg. To 84 deg at approximately 25 MW.

If IGV temperature control is ON, up to 81 % load itremains 54 deg. , after that it is full open.


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SERVO VALVE DRIVER SYSTEM

The gas turbine fuel control system will change fuel flow tothe combustors in response to FSR.

The servo system controls the fuel flow rate by means ofan electro - hydraulic servo valve which ports highpressure hydraulic oil to either side of piston of anactuator as per signal. It is used to open & modulate or toclose fuel passage in the fuel circuit.

Thus servo valve is the interface between the electrical

control system & the mechanical system. It converts anelectrical signal to hydraulic output ( movement ).


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Thank You


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Gas Turbine Control System1 - Nema

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