Model_Steam_Turbine_Gov_System.pdf

7/29/2019 Model_Steam_Turbine_Gov_System.pdf

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ModellingofSteamTurbineand

itsGoverningSystem

DrMSRMurty


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GENERATORCONTROLS


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Grid

Reference

ST : steamturbine

G : generator

SV : stop valve

CV

SV

Steam

Speed

Power

GOVERNINGSYSTEM

GST

CV contr. valve

valve

Fig. 1 STEAM TURBINE GOVERNING SCHEME


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S

P

E

E

D

+

Valve

Position

SET

POINT

-

Mechanical

Power

+GOVERNOR TURBINE ROTOR

INERTIA

Fig2GOVERNINGSYSTEMFUNCTIONALBLOCKDIAGRAM


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GoverningControlsystem

SpeedSensing :Mechanical(Flyballtype),Hydraulic(Pump),Electric(toothed Wheelpickup)

MWTransducerforPower

Processing :Hydromechanical,Electrohydraulic,DigitalElectrohydraulic

Amplification:Hydraulicamplifiersinvariousstages

Actuation:HydraulicServomotor


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TG Unit Operating Modes:Isolated : S Open : Speed changes when gov valve is adjusted

Interconnected : S Closed or grid connected: Speed is unaffected


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TGUnitOnGrid:LoadControl

TGSpeed/Frequency

doesnoteffectgridfrequency

Aftersynchronization,

changeinvalveopeningcannotchangeTGunit

speedbutchangesonly

PowerOutput

InfiniteInertiaBusGRID


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ControlRequirementsStartup: 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 without

much transient overspeed


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Governingsystem:Technology

MechanicalHydraulicControl(MHC)

Electro HydraulicControl(EHC)

Sensing,Processing,primaryamplification

usingelectroniccircuitryTransistorversion(BHEL/KWUSiemens

Iskamaticmodules)

DigitalElectro HydraulicControl(DEHC)

Microprocessorbased


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Processing

Decideshowvalvepositionshouldbechanged

when speedchanges

Objective:Minimumupsetsinthesystem

SpeedController,LoadController:structureandtuningdecidetransientperformance

Droopcharacteristic(4%or5%):important

governingparameter


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ElectronicControllerFeatures

SeparationofSpeedControlandLoad(Power)

Controlfunctionswithseparateprocessingphilosophy

SpeedController:Proportional Derivative

action:AnticipatoryControl

LoadController:Proportional Integralaction

InteractionwithATRS andTSE


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SimpleSpeedgoverningsystem

/Gate

Command

Gate

Oil

ServomotorSENSING

PROCESSINGAMPLIFICATIONANDACTUATION

SETPOINT


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Steam

Actuation of Valve(Servomotor)

HydraulicAmplification

Speed&MW

PrimaryAmplification

Sensing

Processing

Electro-hydraulicConverter

ControlValve

EH

HYDRAULICPART

ST

G

ELECTR

ONICPART

Fig 3 ELECTRO HYDRAULIC GOVERNOR SCHEME


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VALVEOPENINGCOMMAND

Load

Speed

+

+

Load

Ref.

SpeedRef.

SPEEDCONTROLLER

(PDP)

LOAD

CONTROLLER( P I )

SELECTIONLOGIC

(MIN MAX)

Fig 4 SPEED CONTROLLER AND LOAD CONTROLLER IN EHG


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DroopCharacteristic

Speed

Change

Turbine

Power

Change

=(Load)

Valve

Opening

Change

SteamFlow

Change

Load%

SpeedOr

Frequency

104%

100%

0 50 100

52Hz

50Hz


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Frequency(Hz)

50

52

4% Drop

Load0% 50% 100%

Fig 6 REGULATION OR DROOP CHARACTERSTIC


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Time

(Sec)

Speed(%)

Unstable

Oscillatory(Hunting)

Fig 7 TYPICAL SPEED HUNTING TRANSIENT


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ValveOpening

Dead band or insensitivezone

Speed /

frequency

Fig. 8 DEAD BAND

CHARACTERISTIC


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STEAMTURBINESCHEMEWITHHPANDIPCONTROLS

Reheate

r

IPCV

HPCVSteam

Condenser

LPTHPT IP

TG

R H


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TransferFunctionofSteamVolumeSteamVessel

Steaminflow Steam

outflow

Steampressure

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

Wi W o


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Functionalblockdiagramofturbinegoverningsystem


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TURBINECONTROLLER

29

Feed 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


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PI

t

Output

(Y)

t

PDP

K

Output

(Y)

SpeedController LoadController


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Parametersinfluencingtheperformance

RotorInertia

Droop

Speed/LoadController parameters

Deadband Valvecharacteristics

IPTurbinecontrol

Pressurecontrolmodes


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GovernorRegulationorDroop

4%Droop:4%SpeedChangewillcause100

%changeinPowerOutput(Gain:25) Droopisnecessaryfor

i)Sharingofloadii)Ensuringclosedloopstability:Lowervalueof

droopincreasesgainandmakesthesystem

oscillatory


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GoverningSystemResponse

Responsetimesareimportant:delayin

correctioncancausetransientspeedrisehighandtriptheturbine

Stabilityofgoverningsystemdependsonprocessingalgorithm(PI,PID,PDPetc.,)and

onsystemparameters&timeconstants


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Performancespecifications:LoadRejection

Rejectiontozeroloadfromanyload

Speedshallbereturnedtothesetpointasmaybemodifiedbyspeeddrooporregulation

Nomorethanoneunderspeeddeviation

exceeding5%

Nomorethanoneoverspeeddeviationexceeding5%afterinitialoverspeed

deviation


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Performancespecifications:Sustained

conditions

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

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

powerstabilityindex.


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StabilityIndex:Degreeofstability

Judgedbythemagnitudeofsustained

oscillationsofspeedandpoweroutputfromtheturbinethatareproducedbythegovernor

system

Stabilityindexillustratestheregulatingperformanceforthegovernorandturbine

GovernorDeadbandillustratestheperformanceforthegovernoralone


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LoadRejection

GoverningSystemPerformancecanbejudged

byfullloadrejectionbehavior:TransientSpeedRise(TSR),hunting

EmergencyGovernorshouldnotgetactivated

Influencingparameters:RotorAccelerationTime(Ta),Droop,SpeedControllergains,

Incrementaldroop


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LOADREJECTIONRESPONSELoad

100%

Time(sec)

t

100%

0%

Speed(%)

TSR

(6 10%)

5%Droop


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3

FW

SH1

Q

DRUM

WW

BOILER

SH2

G

Q

150ata540C

H

T

P

IP

T

COND

RH

.

.

.

Flue

Gas

Fuel

Air

DESH

Interaction withBoilerControls

GOVERNOR

MasterPressureControl

DrumLevelcontrol

Temperature

Control

Spray


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Extraction

SteamPressure

STEAM

CONDENSER

LPCV

LOAD

SPEED

HPT

LPT

G

GOV,

SYSTEM

HPCV

TO PROCESS

EXTRACTION TURBINE CONTROL SCHEME


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StreamGenerators

LP

Process

VHP HP MPPRDS

Process ProcessProcess

HRSGs

UBs

G

TypicalSteamandPowerSystemHeaders

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

Kg/Cm2 o C

C

G

GAS TURBINE

G

SteamTurbine


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SteamandPowersystemDynamics

Steam

System

Power

System

Fuel

System

Upsets in one system can influence the other


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ModellingandSimulation


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Instantaneous response AssumesuddenLoadReductionandinstantaneouschangein

generation

1.0

.8

Power

p.u Load,PL

Time(Sec.)

GenerationPg

Frequency

Time(Sec.)

50Hz


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RotorInertia

Atsteadystate:

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

Speed= ((Pm Pel)/Ta)dt

Ta=Accelerationtimeorinertiaconstant(functionofmomentofinertia)

Typicalvalues:Ta=9 12sec


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Acceleration/Deceleration

me

Pg

Deviationareaisindicativeof

acceleration/deceleration

PL


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PL me

Pg

DelayduetothecumulativeeffectsofGovernor,hydraulicpassages,turbine

n or f

t

Frequency or Speed

variation

Due to the above :

GovernorResponse

SettlingSpeedhigher


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Xp

Hydraulicrelaystimeconstant

Inflow(Qi) Xp

Qi=volumetric

displacementofoil

=Ap.dxsm/dt

KpXp=Apsxsm

Xsm

Xsm1

Tsm.S

Xp

bLevergain

HP TURBINE TIME CONSTSANT


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HPTURBINETIMECONSTSANT

T4 = Steammassinsideturbine

MassflowthroughHPturbine Kg/Sec207.4

VolumexDensity

=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.


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NALCO


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NALCO


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GNFC Bharuch


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GNFC Bharuch


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GNFC Bharuch


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GNFC Bharuch


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Date post:	14-Apr-2018
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Model_Steam_Turbine_Gov_System.pdf

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