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  • ModellingofSteamTurbineanditsGoverningSystem

    DrMSRMurty

  • GENERATORCONTROLS

  • Grid

    Reference

    ST : steam turbineG : generator

    SV : stop valve

    CV

    SVSteam

    Speed

    Power

    GOVERNINGSYSTEM G

    ST

    CV contr. valve valve

    Fig. 1 STEAM TURBINE GOVERNING SCHEME

  • SPEED

    +

    Valve

    Position

    SET

    POINT -

    Mechanical

    Power

    +GOVERNOR TURBINE ROTOR

    INERTIA

    Fig2GOVERNINGSYSTEMFUNCTIONALBLOCKDIAGRAM

  • GoverningControlsystem

    SpeedSensing :Mechanical(Flyballtype),Hydraulic(Pump),Electric(toothedWheelpickup)

    MWTransducerforPower Processing :Hydromechanical,Electrohydraulic,DigitalElectrohydraulic

    Amplification:Hydraulicamplifiersinvariousstages

    Actuation:HydraulicServomotor

  • TG Unit Operating Modes:Isolated : S Open : Speed changes when gov valve is adjustedInterconnected : S Closed or grid connected: Speed is unaffected

  • TGUnitOnGrid:LoadControl

    TGSpeed/Frequencydoesnoteffectgridfrequency

    Aftersynchronization,changeinvalveopeningcannotchangeTGunitspeedbutchangesonlyPowerOutput

    InfiniteInertiaBusGRID

  • ControlRequirements Startup: To control machine speed forproper synchronization

    Normal Operation: To Control MW and Toparticipate in the control of system frequency

    Emergency: Load Rejection/Circuit BreakerOpeningTo restore speed deviation quickly withoutmuch transient overspeed

  • Governingsystem:Technology

    MechanicalHydraulicControl(MHC) Electro HydraulicControl(EHC)Sensing,Processing,primaryamplificationusingelectroniccircuitry

    Transistorversion(BHEL/KWUSiemensIskamaticmodules)

    DigitalElectro HydraulicControl(DEHC)Microprocessorbased

  • Processing

    Decideshowvalvepositionshouldbechangedwhenspeedchanges

    Objective:Minimumupsetsinthesystem SpeedController,LoadController:structureandtuningdecidetransientperformance

    Droopcharacteristic(4%or5%):importantgoverningparameter

  • ElectronicControllerFeatures

    SeparationofSpeedControlandLoad(Power)Controlfunctionswithseparateprocessingphilosophy

    SpeedController:Proportional Derivativeaction:AnticipatoryControl

    LoadController:Proportional Integralaction InteractionwithATRS andTSE

  • SimpleSpeedgoverningsystem

    /Gate

    Command

    GateOil

    ServomotorSENSING

    PROCESSING AMPLIFICATIONANDACTUATION

    SETPOINT

  • Steam

    Actuation of Valve (Servomotor)

    Hydraulic Amplification

    Speed & MW

    PrimaryAmplification

    Sensing

    Processing

    Electro-hydraulicConverter

    ControlValve

    EH

    HYDRAULICPART

    ST

    G

    ELECTRONICPART

    Fig 3 ELECTRO HYDRAULIC GOVERNOR SCHEME

  • VALVEOPENINGCOMMAND

    Load

    Speed

    +

    +LoadRef.

    SpeedRef.

    SPEEDCONTROLLER

    (PDP)

    LOADCONTROLLER

    ( P I )

    SELECTIONLOGIC

    (MIN MAX)

    Fig 4 SPEED CONTROLLER AND LOAD CONTROLLER IN EHG

  • DroopCharacteristic

    SpeedChange

    TurbinePowerChange

    =(Load)

    ValveOpeningChange

    SteamFlowChange

    Load%

    SpeedOrFrequency

    104%

    100%

    0 50 100

    52Hz

    50Hz

  • Frequency(Hz)

    50

    524% Drop

    Load0% 50% 100%

    Fig 6 REGULATION OR DROOP CHARACTERSTIC

  • Time (Sec)

    Speed(%)

    Unstable

    Oscillatory (Hunting)

    Fig 7 TYPICAL SPEED HUNTING TRANSIENT

  • ValveOpening

    Dead band or insensitive zone

    Speed / frequency

    Fig. 8 DEAD BAND CHARACTERISTIC

  • STEAMTURBINESCHEMEWITHHPANDIPCONTROLS

    Reheater

    IPCV

    HPCVSteam

    Condenser

    LPTHP

    T

    IPT G

    R H

  • TransferFunctionofSteamVolume

    Steam Vessel

    Steam inflow Steam

    outflow

    Steam pressure

    1----------(1 + TV. s)

    Wi W o

  • Functionalblockdiagramofturbinegoverningsystem

  • TURBINECONTROLLER

    29Feed forward provision

    KSVSSpeed Controller: Proportional Derivative

    Load Controller : Proportional Integral

    Load

    Load Ref

    SpeedRef SPEED

    CONTROLLER

    LOADCONTROLLER

    SELECTIONLOGIC

    EH

    To Hyd.Amplifier

    speed

    Ks(1+VsTs.S)(1 + Ts . S)droop

    KPL + 1TILS

    KS

  • PI

    t

    Output(Y)

    t

    PDP

    K

    Output(Y)

    SpeedController LoadController

  • Parametersinfluencingtheperformance

    RotorInertia Droop Speed/LoadControllerparameters Deadband Valvecharacteristics IPTurbinecontrol Pressurecontrolmodes

  • GovernorRegulationorDroop

    4%Droop:4%SpeedChangewillcause100%changeinPowerOutput(Gain:25)

    Droopisnecessaryfori)Sharingofloadii)Ensuringclosedloopstability:Lowervalueofdroopincreasesgainandmakesthesystemoscillatory

  • GoverningSystemResponse

    Responsetimesareimportant:delayincorrectioncancausetransientspeedrisehighandtriptheturbine

    Stabilityofgoverningsystemdependsonprocessingalgorithm(PI,PID,PDPetc.,)andonsystemparameters&timeconstants

  • Performancespecifications:LoadRejection

    Rejectiontozeroloadfromanyload Speedshallbereturnedtothesetpointasmaybemodifiedbyspeeddrooporregulation

    Nomorethanoneunderspeeddeviationexceeding5%

    Nomorethanoneoverspeeddeviationexceeding5%afterinitialoverspeeddeviation

  • Performancespecifications:Sustainedconditions

    Steadystategoverningspeedband:Notmorethan0.3%(atnoloadoranyload).Alsocalledspeedstabilityindex.

    Steadystategoverningloadband:Notmorethan0.4%(at5%speeddroop)Alsocalledpowerstabilityindex.

  • StabilityIndex:Degreeofstability

    Judgedbythemagnitudeofsustainedoscillationsofspeedandpoweroutputfromtheturbinethatareproducedbythegovernorsystem

    Stabilityindexillustratestheregulatingperformanceforthegovernorandturbine

    GovernorDeadbandillustratestheperformanceforthegovernoralone

  • LoadRejection

    GoverningSystemPerformancecanbejudgedbyfullloadrejectionbehavior:TransientSpeedRise(TSR),hunting

    EmergencyGovernorshouldnotgetactivated Influencingparameters:RotorAccelerationTime(Ta),Droop,SpeedControllergains,Incrementaldroop

  • LOADREJECTIONRESPONSE

    Load

    100%

    Time(sec)

    t

    100%0%

    Speed(%)

    TSR(6 10%)

    5%Droop

  • 3FW

    SH1

    QDRUM

    WW

    BOILER

    SH2

    G

    Q

    150ata540C

    HTP

    IPT

    COND

    RH

    .

    .

    .

    FlueGas

    Fuel

    Air

    DESH

    InteractionwithBoilerControls

    GOVERNOR

    MasterPressureControl

    DrumLevelcontrol

    TemperatureControl

    Spray

  • ExtractionSteamPressure

    STEAM

    CONDENSER

    LPCVLOAD

    SPEED

    HPT

    LPT

    G

    GOV,SYSTEM

    HPCV

    TO PROCESS

    EXTRACTION TURBINE CONTROL SCHEME

  • StreamGenerators

    LP

    Process

    VHP HP MPPRDS

    Process ProcessProcess

    HRSGs

    UBs

    G

    TypicalSteamandPowerSystem

    Headers

    107/ 510 45/ 400 20/ 340 5.5/ 220

    Kg/Cm2 o C

    C

    G

    GAS TURBINE

    GSteam Turbine

  • SteamandPowersystemDynamics

    Steam System

    Power System

    Fuel System

    Upsets in one system can influence the other

  • ModellingandSimulation

  • Instantaneousresponse

    AssumesuddenLoadReductionandinstantaneouschangeingeneration

    1.0

    .8

    Powerp.u Load,PL

    Time(Sec.)

    GenerationPg

    Frequency

    Time(Sec.)

    50Hz

  • RotorInertia

    Atsteadystate:TurbineTorque(Pm)=LoadTorque((Pel)

    Duringtransient:Speed=((Pm Pel)/Ta)dt

    Ta=Accelerationtimeorinertiaconstant(functionofmomentofinertia)

    Typicalvalues:Ta=9 12sec

  • Acceleration/Deceleration

    me

    Pg

    Deviationareaisindicativeofacceleration/deceleration

    PL

  • PL me

    Pg

    DelayduetothecumulativeeffectsofGovernor,hydraulicpassages,turbine

    n or f

    t

    Frequency or SpeedvariationDue to the above :

    GovernorResponse

    SettlingSpeedhigher

  • Xp

    Hydraulicrelaystimeconstant

    Inflow(Qi) Xp

    Qi=volumetric

    displacementofoil

    =Ap.dxsm/dtKpXp=Apsxsm

    Xsm

    Xsm1

    Tsm.S Xp

    bLevergain

  • HPTURBINETIMECONSTSANT

    T4=Steammassinsideturbine

    MassflowthroughHPturbineKg/Sec207.4VolumexDensity=0.844(m3)(1/0.02337) =36.114

    T4=36.114/207.4=0.17Sec.

    VHPincludes: Volumeininletportionupto1st stage.

    allpipingconnections blading

    IPTurbine:0.27Sec

    LPTurbine:0.47Sec

    TReheaterr :10to20Sec.

  • NALCO

  • NALCO

  • GNFC Bharuch

  • GNFC Bharuch

  • GNFC Bharuch

  • GNFC Bharuch