Training On Gt Controls

Training on GT Controls

Introduction to Control Philosophy A Gas Turbine Consists of 1. 2. 3. 4. 5. 6. 7.

Starting means Auxiliaries Compressor Combustion System Turbine Exhaust Load

Introduction to Control Philosophy Control system Communicates with the turbine to Measure, adjust the parameters

The Main Inputs are Air & Fuel and the Outputs are Load & Exhaust Gases.

It also protects the turbine from abnormal operations

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

Simplified control schematic

Min Value

Example of Minimum FSR of Six Control Loops on HMI Screen

Detailed Control Schematic

We will use this as reference as we go in detail of the course

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

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

Speed Control Characteristics Droop speed control is a proportional control, changing FSR in proportion to the difference between actual 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

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 to measure and hence the Controller uses the exhaust thermocouples as reference which is directly proportional to Firing Temperature Tf = Tx (Pcd/Pa) k

Exhaust/Firing Temperature Relation

Curve comparing the load

at different ambient

The firing temperature remains constant even with increase in MW, FSR & CPR ratio with less exhaust temperatures

Temperature control scheme

FSRT is the minimum of the Six Control Loops

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_K Isothermal

TTKn_I TTKn_C

CPD FSR

Protection of Turbine internals and optimum power

Acceleration control

0.35 %/sec

0.10 %/sec 0%

40% 50% 75% 95% 100%

TNH Acceleration Control functions during sudden Load Changes and Start Up

Manual control

Manual Control Loop Can be used to limit fuel to prevent over firing and over riding active control

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

IGV Control IGV Control Loop • Controls air fuel ratio • Prevents Compressor

Pulsations

IGV Control

IGV scheduling is required to ensure the protection from Pulsation/Stall by excessive opening at lower speeds/loads and negative pressures at partial loads by less opening

IGV Schedule Maintains higher Exhaust Temperature at partial loadsfor Combined Cycle Operation

IGV Control Isothermal

The exhaust temp. varies for simple and combined cycle operations. IGV temperature control never exceeds the base temperature control set point

CPD

IGV control reference Maintains higher Exhaust Temperature at partial loads for Combined Cycle Operation

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.

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

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

Gas Fuel Control Scheme

Fuel Gas Control System consists of Stop ratio Valve, Gas Control Valve Controls

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

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

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.

IGV Control scheme VSVO

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

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

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

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