FREE GOVERNOR MODE OF OPERATION(FGMO)FORSTEAM TURBINES

ORGANISATION OF PRESENTATIONWhat is FGMO ?IEGC guidelinesFacilities available in KWU design sets of BHELProblems in implementation of FGMOModifications carried in control schemeConclusion

FREE GOVERNOR MODE OPERATION (FGMO)It means that the governor is free to govern as per its regulation/droop characteristicsThere are no constraints imposed on it like - Valve kept wide open - frequency influence switched off - dead band for frequency influence - delibrate time delays

OBJECTIVE OF FREE GOVERNOR MODE OF OPERATION To arrest transient swings in grid frequencyTo maintain national grid frequency within IEGC band of 49 to 50.5 HzFree governor operation allows the machine to load or unload depending upon whether frequency is lower than or more than the reference frequencyVariation in grid frequency can be minimized by putting all the generating stations on free governor mode of operation

STEADY STATE SPEED REGULATION (DROOP)IT IS THE CHANGE IN STEADY STATE SPEEDEXPRESSED IN % OF RATED SPEED, WHEN THE OUTPUT OF THE TURBINE IS GRADUALLY REDUCED FROM RATED POWER DOWN TO ZERO POWER WITH IDENTICAL SETTINGS OF ALL ELEMENTS OF THE SPEED GOVERNING SYSTEM

DROOP CHARACTERISTICS30003150Droop = (3150-3000) /3000 *100 = 5%

Chart1

3150

3120

3090

3060

3030

3000

0

5% droop

Load %

Speed (rpm)

Sheet1

% droopMW/hz

8125

freq5%8%

0315050

20312050

40309043.75

60306037.5

80303031.25

100300025

18.75

12.5

6.25

75

-6.25

-12.5

-18.75

-25

-31.25

-37.5

-43.75

-50

-50

-50

Sheet1

00

315050

312050

309043.75

306037.5

303031.25

300025

018.75

12.5

6.25

75

-6.25

-12.5

-18.75

-25

-31.25

-37.5

-43.75

-50

5% droop

8% droop

freq

influence

characteristics with different droops

Sheet2

Sheet3

EXAMPLE OF NORTHERN GRIDTotal installed capacity= 28000 MWNormally available power (approx.) = 17000 MWPeak load demand in a day (approx.) = 19000 MW

Hence total shortfall in a day = 2000 MW (approx. 10%)Therefore, variation in grid frequency should not be more than 0.25 Hz (=0.1*2.5Hz). But in actual the variation in frequency is of the order of 1-1.5 Hz.

ASSUMPTION :- DROOP = 5 %

THIS MEANS THATGovernors are operating in locked conditionTo enforce grid discipline, CERC issues guidelines for implementation of FGMO

INDIAN ELECTRICITY GRID CODE (IEGC)SECTION 6.2 (E) ALL GENERATING UNITS, WHICH ARE SYNCHRONISED WITH THE GRID, IRRESPECTIVE OF THEIR OWNERSHIP, TYPE AND SIZE, SHALL HAVE THEIR GOVERNORS IN NORMAL OPERATION AT ALL TIMES. IF ANY GENERATING UNIT OF OVER FIFTY (50) MW SIZE (10 MW FOR NORTH EASTERN REGION) IS REQUIRED TO BE OPERATED WITHOUT ITS GOVERNOR IN NORMAL OPERATION, THE RLDC SHALL BE IMMEDIATELY ADVISED ABOUT THE REASON AND DURATION OF SUCH OPERATION. ALL GOVERNOR SHALL HAVE A DROOP OF BETWEEN 3% AND 6%

INDIAN ELECTRICITY GRID CODE BHEL sets meet the requirement of droop

LMW Turbine - 4% Siemens Turbine - 2.5% to 8% in EHC mode 5% in Hydraulic mode

INDIAN ELECTRICITY GRID CODE (IEGC)SECTION 6.2 (F) FACILITIES AVAILABLE WITHIN LOAD LIMITERS, AUTOMATIC TURBINE RUN UP SYSTEM, TURBINE SUPERVISORY CONTROL, CO-ORDINATED CONTROL SYSTEM ETC. SHALL NOT BE USED TO SUPPRESS THE NORMAL GOVERNOR ACTION IN ANY MANNER. NO DEAD BAND AND / OR TIME DELAYS SHALL BE DELIBERATELY INTRODUCED.

INDIAN ELECTRICITY GRID CODE (IEGC)SECTION 6.2 (G) ALL GENERATING UNITS, OPERATING AT / UP TO 100% OF THEIR MAXIMUM CONTINOUS RATING (MCR) SHALL NORMALLY BE CAPABLE OF (AND SHALL NOT IN ANY WAY BE PREVENTED FROM) INSTANTANEOUSLY PICKING UP FIVE PERCENT (%) EXTRA LOAD FOR ATLEAST FIVE (5) MINUTES OR WITHIN TECHNICAL LIMITS PRESCRIBED BY THE MANUFACTURER WHEN FREQUENCY FALLS DUE TO SYSTEM CONTNGENCY.

INDIAN ELECTRICITY GRID CODE (IEGC)SECTION 6.2 (H) THE RECOMMENDED RATE FOR CHANGING THE GOVERNOR SETTING, I.E. SUPPLEMENTARY CONTROL FOR INCREASING OR DECREASING THE OUTPUT (GENERATION LEVEL) FOR ALL GENERATING UNITS, IRRESPECTIVE OF THEIR TYPE AND SIZE, WOULD BE ONE (1.0) PERCENT PER MINUTE OR AS PER MANUFACURERS LIMITS. HOWEVER, IF FREQUENCY FALL BELOW 49.5 Hz, ALL PARTY LOADED GENERATING UNITS SHALL PICKUP ADDITIONAL LOAD AT FASTER RATE, ACCORDING TO THEIR CAPABILITY

REALISATION OF DROOP CHARACTERISTICSIn hydraulic control mode these are inherent in the governing system (as the system acts to control speed)In electrical controller, these are built-up through frequency influence on load setpoint (as the system acts to control load)

CHARACTERISTICS OF FREQUENCY INFLUENCEDroop = 4 %Droop = 8 %485250Frequency (in Hz)+50 %- 50 %Load4951

TSE INFLUENCELOADGRADIENTFREQUENCYINFLUENCECORRECTED LOAD SETPTFREQUENCY INFLUENCE SCHEME(ORIGINAL)++50 HzF-ACT.LOAD SETPOINT

TSE INFLUENCELOADGRADIENTFREQUENCYINFLUENCECORRECTED LOAD SETPTFREQUENCY INFLUENCE SCHEME(ORIGINAL)++500MWFREQ. = 50Hz0 MW500MW500MWFREQ. = 49.875HzLOAD CHANGE = 5% i.e. 25MW+25 MW525MWLOAD SETPOINT

Under FGMO, there is a lot of load cycling and corresponding fatigue in equipmentParametric variations are beyond allowable limits , leading to unsafe operation.Utilities find it very difficult to implement supplementary control manuallyBoiler is the weak link, it does not have the necessary reserves and there is an inherent delayDIFFICULTIES FACED BY UTILITIESNTPC, AGENCO, MSEB PRESENTED THE FOLLOWING VIEWS

STEERING COMMITTEA high level committee set up by CEA to examine the issueView points of Utilities, OEMs, PGCIL and CERC heard by the committeeAfter deliberations, certain actions were suggested to BHEL and NTPC to address the issues raised by utilities

To develop a control scheme with floating frequency as the frequency can vary between 49 to 50.5 Hz. The scheme should also automate the process of supplementary control i.e. Load change after 5 minutesThe modified control scheme to be tested at simulatorTo suggest suitable changes in the existing control logic of EHC and CMC for safeguarding the boiler, turbine, generator from the effect of rapid changes in frequencyRECOMMENDATIONS BY COMMITTEE

MODIFIED CONTROL SCHEME OBJECTIVESReference frequency shall be floating between 49.0 to 50.5 Hz, depending on operating frequency For any frequency change, load change shall be immediate and limited to +/-5%.Load change is to be sustained for approx. 5 minutes. If frequency varies during this period, corrective action to be taken againContd.

OBJECTIVESLoad shall be brought back to the setpoint in a ramped fashion after five minutesFor frequency < 49.0 and >50.5 Hz , load change to be as per droop characteristics and limited to +/- 10%

MODIFIED SCHEME

First scheme developed by BHEL and tested at Simhadri simulator at Corporate R&D on 17/07/2004Step and ramp change in load were simulatedParameter variations were within allowable limitsIt met the set objectives. However, certain changes were suggested Results were presented to NTPC/ CEA/ PGCIL etc. In 4th and 5th committee meetings. 5th meet was held at HardwarIt was suggested by Chairman that the scheme be tested at Simhadri site by BHEL & NTPC

Floating Frequency SetpointFactFrefPFdev

TSE INFLUENCELOADGRADIENTFREQUENCYINFLUENCELOAD SETPOINTCORRECTED LOAD SETPTFREQUENCY INFLUENCE SCHEME(PROPOSED)++F-ACT.F-PREVF+-+5%(49-50.5)TO CCF-ACT 50.5FREF=49/ 50.5F+-+10%TO CCCC- COMBUSTION CONTROL

BLOCK DIAGRAM - CONTROL SCHEME

SIMHADRI SITE TRIALSScheme was further fine-tuned before and during field trialsDead band of 0.03Hz was introducedTrend curves were plottedThese were analyzed and parametric variations were deduced

SUMMARY OF TEST RESULTSREVISED FGMO SCHEMEApprox. 45 load cycles in a day for SR frequency+ 15 Deg C variationM.S. TEMP+ 10 Deg C variation H.R. TEMPNearing Alarm ValuesRH METALTEMPSTHROTTLEPRESSURE5 kg/sq.cm variationsLOAD Turbine metal temperatures hardly undergo any change for this load variationWith full thermal reserve, the max. load increase is 3 %

CONCLUSIONModified scheme has been accepted by CEA and NTPC Final report of the committee has been released directing utilities to implement FGMOScheme to be implemented by utilities for KWU design setsUtilities have to place order on BHEL for this workAs of now, LMZ design sets to be put in FGMO (without any modification) and controlled manually

Broad features of Scheme implemented at NasikThe scheme with following basic features was implemented in unit 4 (210 MW LMZ m/c) at NasikLoad and Turbine inlet Pr changes with frequency variation. Pressure correction through pulse command to speeder gear motor to restore load when rate of pressure variation is more than 0.2 Kscm/min Pressure correction through continuos command when pressure variation is more than 2 KscmNo changes in fuel firing.

A team led by Member, CERC visited Nasik and was satisfied with the response of the scheme

MS. Pr. > (SET POINT + 2)

S

SPEEDER GEARRAISE COMMAND8 SEC.

MS. Pr. > (SET POINT - 2)

LOOP IN AUTO

RTHIS RELATES TO THE CASE OF FREQUENCY RISELOOP IN AUTO

SCHEME IMPLEMENTED IN NASIK (MSEB)

SCHEME IMPLEMENTED IN NASIK (MSEB)

MS. Pr. > (SET POINT - 2)

S

SPEEDER GEARLOWER COMMAND

8 SEC.

MS. Pr. > (SET POINT + 2)

LOOP IN AUTO

R

THIS RELATES TO THE CASE OF FREQUENCY FALL

LOOP IN AUTO

*