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CMC

(COORDINATED MASTER

CONTROL)

RS Rajput

Supdt.(C&I)

NTPC Ltd Korba August 2nd, 2012 Simulator, Korba

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Coordinated Master Control system is an ultimate or

highest level of automation of the power plant.

CMC ensures proper coordination between boiler and

turbine in order to attain enhanced unit level response, while

maintaining the outputs of boiler, turbine and all major plant

auxiliaries within safe operating limits.

When operated in coordinated mode, most of the

important control loops responds to the central command

(Unit Master).A coordinated control system develops control signals

simultaneously for the regulation of the boiler's firing rate and

for the positioning of the turbine control valve.

COORDINATED MASTER CONTROL

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How changes in boilers

firing rate or turbine

control valve position

affects the throughput of the

power plant.

Fundamentals:

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Fundamentals:

If a step change is given in the turbine valve, this results in the

transient change in load and steady state change in pressure.

Whereas step change in the firing rate of boiler, results into a

permanent steady state change in both load and pressure

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Permanent change in MW output can be

obtained only by changing the boiler firing

rate

whereas change in turbine valve positionwill result in only momentary change in MW

but permanent change in throttle pressure.

It means that..

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If parallel step change in both turbine control valve andboiler firing rate results in overshoots/undershoots in

throttle pressure and MW curves.

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The load reflects the initial change by the opening of

the turbine valve but immediately starts to decay as

the pressure decays until the effect of increased fueland air is felt within the boiler.

But in such case, if turbine valve lift is delayed by

an amount equal to process delay in generationof steam pressure in the boiler (delay caused by

coal feeders, pulverisers and Boiler Inertia), this

will result into a constant throttle pressure

without any decay. And there will not be anyovershoots/undershoots in MW or throttle pressure

curves.

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CMC in action

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Turbines control valves are fast responding components

and Boiler is having transport lag and Thermal inertia and

hence delayed respond with variation in command.

Turbine will be able to meet MW demand or main steam

pressure set point quickly by positioning its control valves.

But Turbine will be able to maintain only one unit

parameter MW or main steam pressure.The other has to becontrolled by the Boiler.

Conclusion

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The above philosophy has been utilized in the

development of the CMC. CMC basically tries to ensureproper coordination between the slow Boiler and fast acting

turbine control valves.

It ensures that there isnt mismatch between boiler

steam generation and electric load generated by turbine-

generator for long durations.

Depending upon how CMC forms coordination between

boiler and turbine, there are following four modes of

operation:-

1. Boiler Follow Mode2. Turbine Follow Mode

3. Co-ordinated Mode

4. Runback

CMC

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1) CMC: Basically to control internal parameters of

unit like (1) M S Pressure, (2) Load. Also to coordinatesensitive turbine and slow response of boiler auxiliaries,

Good for grid and Unit stability. Both Boiler and Turbine

controls are ON Auto.

2) BFM: Boiler follows turbine. Turbine on Loadcontroller & Boiler is ON Auto, controls pressure with BLI

as feed forward. MW demands are met by Turbine and less

importance to unit stability.

3) TFM: Turbine follows Boiler. Boiler Master onmanual control. Pressure control. Turbine maintains pressure

by varying MSCV ,Unit load depends on steam output from

boiler Best for unit stability

CMC: Definitions

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04) RUNBACK mode:

Boiler controls give command in proportion to unit capability.

TurbinePressure Control.

05) BOILER MASTER:

Basically a pressure controller

FEED FORWARD SIGNAL

GNI OUTPUT - CMCBLI - B.F.M

PRTD - T.F.M

GET BYPASSED - in R/B

F/F Pr. Set point Actual pressure

Boiler Master

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06) G N I :

Control tracking generator orset point control module. Generates

increase/decrease rate.

Target to GNI:

CMC : Load dispatch center or unit- master

[frequency corrected]

BFM : Boiler demand (BM O/P)

TFM : Actual Load.

R/B : Unit capability

07) UNIT CAPABILITY:

Capability to produce MW at that instant, UC signal depends on

the number of auxiliaries in service and their contribution is

expressed as MW signal, which is the max. they can support.

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08) FGMO:

Free Governing mode of operation Introduces critical externalparameter i.e. grid frequency to our control system.

To ensure stability of grid it is necessary to have frequency

regulation in CMC/EHC. But frequency is network parameter,which can not be controlled by few units in the network. Totaldisturbance in network will be passed on to the units havingregulation by the many units do not have regulation.

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BOILER FOLLOW MODE

1. Turbine on load controllimit pressure.

2. Boiler master on Auto, controls throttle steam Pressure

with steam flow as feed forward. Varying fuel I/P (firing

rate) into the furnace.

In this mode boiler has to supply the steam for

whatever load has been set from Turbine desk. In this way

if the throttle steam reaches a limit (10 kg below the set

throttle steam Pr.) limit Pr. Engaged condition comesand load would be scarified to maintain/restore the

throttle steam Pr.

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Boiler follow mode gives more stability to the grid as

MW demand are met by turbine quickly and lesser

importance to unit stability, because the action by

Turbine will be disturbing main stream pressure.

Advantage of boiler follow mode:

It provides maximum stability to network

the storage capacity of the boiler is meaningfully used &

the resulting changes are corrected by the fuel flow.

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MW SET

PT.

G

MW F

T

+ - PR.B

FUEL

FIRING

DEVICE

+ -

U

PID PI

F

P

-

BOILER FOLLOW MODE

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SELECTION OF BOILER FOLLOW MODE ( BFM)

1. Put air control on auto (at least one FD fan)

2. Put feeders speed control on auto after varying fuelmaster(FM) output and making feeder speed controller errorzero.

3. Vary Blr. Master O/P so that FM error becomes zero. Then putFM on auto.

4. Make throttle pr. Set point and actual pr. Difference zero.

5. Put BM on auto.

If unit in turbine follow or coordinated mode change over toboiler follow occurs under following condition :-

turbine goes to manual because of any reason or operatoraction

PrCMC - PrLim > 60MW

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TURBINE FOLLOW MODE: -

1. Boiler manually controlled

2. Turbine master On Auto -controls throttle steam Pre. (With

steam flow as feed forward) by varying load.

In T.F.M Pr. Controller comes into picture and the throttle

Steam Pressure varies the opening of MSCV to maintain the

set throttle steam Pre.

TFM gives maximum stability to unit operations with slow

response to grid requirements by initiating combustion

controls first and turbine valves positioning after steam

production.

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MW SET

PT.

PI

G

NF

T

+PR.

SET PT.

B

PI

FUEL

FIRING

DEVICE+

-

-

-P

TURBINE FOLLOW MODE

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SELECTION OF TURBINE FOLLOW MODE ( TFM)

1. Boiler master on manual.

2. Throttle pressure deviation zero.

3. Turbine in auto.4. Press. Turbine flow push button along with manual release on

CMC desk and turbine goes to initial pressure mode fromLMT mode by itself.

5. Now load set point can be changed by varying the boiler

master manually.

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CMC controls the Unit, treating boiler and turbine as a unit. Its

aim is to generate desired MW O/P through coordinateregulation of boiler I/P & O/P (turbine I/P). Turbine must not

increase load without taking firing /boiler inertia in consideration.

CMC coordinates sensitive turbine & slow response boiler&

Auxiliaries.

IN CMC Boiler master is on Auto

Turbine is on Auto

Unit master - Receiving load demand from

ALDC or Manually from desk.

CMC sets the MW set point which will be pursued by boilermaster by taking throttle pressure error as final trimming input

signal.

CMC

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Turbine will control the MW by taking MW error as input.

Th.pr. error will not be effecting the the MW till it is

beyond limits.

Boiler master will change the air & fuel to provide the

desired steam. The response will be slow, compared to

turbine response. This mode of operation gives maximum

stability to the units with optimum response taking boiler &

turbine as a unit.

CMC contd..

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In CMC, turbine maintains the load and boiler maintains the

throttle pressure.

On change in unit load demand / MW set point or Steam

Pressure set point, first boiler firing changed for building up

the desired energy level in the form of steam pressure and

then signal is forwarded to the turbine for change of desiredload.

For coordinated mode both boiler and turbine should be

in auto.

This mode of operation provides facilities of Frequencyinfluence, Runback, increase block, decrease block, run

up and run down.

CMC contd..

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Runback Mode:

On tripping of any of the unit auxiliaries, the unit capability of

generating full load is reduced and unit stability is threatened.

In orderto enhance the stability of unit on tripping of the

auxiliaries, Run Back Action is initiated to maintain the critical

parameters within safe limits, until the tripped equipment or its

standby is brought back into operation.In Runback condition boiler load setpoint is reduced to Unit

capability and hence unit load. And turbine is forced to initial

pressure control mode (turbine will try to maintain steam

pressure exactly at its setpoint).

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CMC: Modes summary

CO ORDINATED MASTER CONTROL 200MW

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CO-ORDINATED MASTER CONTROL: 200MW

CO ORDINATED MASTER BLOCK DIAGRAM

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CO-ORDINATED MASTER BLOCK DIAGRAM

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COORDINATED MASTER CONTROL BOILER MASTER

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COORDINATED MASTER CONTROL LOAD DEMAND

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FIRING RATE CONTROL FUEL FLOW

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FIRING RATE CONTROL AIR FLOW

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COORDINATED MASTER CONTROL RUN BACK

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Pressure Correction in CMC

Under normal operating conditions including small load (pressure)

variation boiler and turbine are controlled independently as per set point from

GNI. Any unbalance in power generation and power consumption due tofrequency variation in FGMO , throttle pressure may increase or decrease

which may cause dangerous condition in the boiler.

If DP (Set throttle pre.- Actual throttle pre.) variation goes below set

point ( - ve pressure deviation) , boiler storage capacity is used. However, any

large variation in throttle pressure shall restrict the Turbine output till the

Boiler has produced the additional output to match the increased demand.

Similarly in case of +ve pressure deviation turbine output will increase.

MW

2 Kg

- DP

15MW

1 Kg

15MW

1 Kg2 Kg

+ DP

Note:-

THROTTLE PRESSURE (DP) correctionstarts at +/- 1Kg and acts upto +/- 2Kg.It will add or subtract +/- 15 MW to theGNI output, thereby generatingpressure corrected GNI output to EHC.

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+

+

-

Max

nMin

P

Th.Pre.

Set.Pre

F/F

Pre. Correction

Adder

Adder

O/p

K F

Min

Unit

Master

GNI

M

AX

M

I

N

Boiler master

PI+D

Delay

Frequency connected

GNI O/P

Frequency & Pr.Connected GNI O/P to EHC

P

+

-

--

+

+

Air master Fuel

master

FREQUENCY INFULENCE ON CMC

1.5 %

MW

2992

301210

MW

20

MW

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COORDINATED MASTER CONTROL LOGIC DIAGRAM

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X Y PA

BP

P

Y1

Y2

Y2Y1

28.6%85.7%

3X1.01

X001 XM03 XP01 PT3 X001

CV

CORRECTED

COAL FLOW

A

B

TOTAL OIL FLOW

MW GENERATED

XP01

TOTAL COAL FLOW

-

++

-

+ +

B/M O/P AIR

MIN

FUEL MASTER

A B J

CV Correction loop manipulates the coal

flow measurement signal by increasing or

decreasing it, to show less coal is going

when coal quality is bad and more whencoal is good the effect is limited to 85% to

100% of actual coal flow

CV CORRECTION

LOOP

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O2 Correction -

A section station and a setter for oxygen set point are

provided to achieve the desired excess air. If variable O2 set

point (SP) is selected, set point is generated by a function

generator which is a function of max ( air flow SP and total air

flow). In other mode SP is set from UCB. O2 in flue gas iscompared with this SP and error is fed to PI controller, output

of which is limited between 0.8 and 1.2% of total air flow.

O2 Correction loop manipulates the total airflow measurement

by increasing or decreasing O2 master to show less air/more air

is flowing. This influence is limited to 30% of the total air flow

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SELECTION OF CMC

1. Put air control on auto (at least one FD fan)

2. Put feeders speed control on auto after varying fuelmaster(FM) output and making feeder speed controller errorzero.

3. Vary Blr. Master O/P so that FM error becomes zero. Then putFM on auto.

4. Make throttle pr. Set point and actual pr. Difference zero.5. Put BM on auto.

6. Increase /decrease unit master output so that it becomesequal to actual load. (wait unit load set value and loadvalue matches as shown in the CMC panel digitalindicator).

7. Form TG desk put turbine control on auto.

8. Press coordinated push button along with manual releaseon CMC desk.

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CMC summary: recap..

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