CMC (COORDINATED MASTER CONTROL)

CMC ensure proper coordination between Auxiliaries, boiler and turbine to attain efficient and safe running of the plant. In thermal power units the turbines are fast responding components& boilers are having transport lag & thermal inertia Hence delayedly respond with variation in command. Turbine will be able to control the load or th.pre. quickly by changing the position of control valves. The other parameter are to be controlled by boiler master. The mode of operating the units as follows. (1) CMC coordinated mode (2) BOILER follow mode- Boiler follow turbine (3) Turbine follow mode- Turbine follow Boiler (constant Pr. Mode) (4) RUNBACK MODE.

Definitions:

1)

CMC:

Basically to control internal parameters of unit like (1) M S Pressure, (2) Load. Also to coordinate sensitive turbine and slow response of boiler auxiliaries, Good for network and Unit stability. Both Boiler and Turbine control ON Auto. 2) BFM:

Boiler follow turbine. Turbine on Load control- Boiler ON Autocontrol pressure with BLI as feed forward. MW demands are met by Turbine firstly and lesser importance to unit stability. 3) TFM:

Turbine follow Boiler. Boiler Master on manual control. Pressure control. Turbine maintains pressure by varying MSCV ,Unit load depends on steam output from boiler Best for unit stability

RUNBACK MODE. under runback conditions the firing for the boiler must be reduced to preset values, as close as possible to the tolerable limits. Therefore the swings of firing rate caused by the action of the PID controller must be avoided. As consequence of this condition the system has to switched to pure feed forward to control where the firing rate set point is directly proportional to load capability signal. To avoid any mismatch between steam production of the boiler and the turbine load turbine has to be switched to initial pressure control.

04)

RUNBACK:

In R/B mode boiler controls give command in proportion to unit capability. Turbine Pre. Control. R/B mode sets in automatically. 05) BOILER MASTER: Basically a pressure controller F/F Pre. Set point Actual pressure +

BMFEED FORWARD SIGNAL GNI OUTPUT - CMC BLI - B.F.M PRTD - T.F.M GET BYPASSED - R/B

06) G N I : Control tracking generator or set Generates increase/decrease rate. Target to GNI: CMC : Load dispatch center or unit- master [frequency corrected] BFM TFM R/B : Boiler demand (BM O/P) : Actual Load. : Unit capability. point control module.

07) UNIT CAPABILITY: Capability to produce MW at that instant, W.C signal depends on the number of auxiliaries in service and their contribution is expressed as MW signal, which they can support.

08) FGMO: Free Governing mode of operation Intro duce critical external parameter i.e. freq. of network to our control system. To ensure stability of network or grid it is necessary to have frequency regulation in CMC/EHC. But frequency is network parameter, which cannot be controlled by few units in the network. Total disturbance in network will be passed on to the units having regulation by the many units do not have regulation. 09) CMC TABLEMode Boiler controlsThrottle Pressure Pressure MW & Pressure [Manual at KORBA] Produces steam as per unit capability

Input Turbine controlsMW To Boiler

ControlsPressure error Pressure error Pressure error UNIT Capability Signal

Feed ForwardSteam Flow [BLI] MW error GNI O/P PRTD Turbine load set point BM Bypassed

Input To turbine controlMW error (Load controller active) MW error (Load controller active) Pressure error

BFM CMC

MW Throttle- pressure (Pressure controller active) Throttle- pressure (Pressure controller active)

TFM

RUN BACK

Pressure error

BOILER FOLLOW MODE1. Turbine on load control 2. Boiler master on Auto-controls throttle steam Pressure with steam flow as feed forward. Varying fuel I/P (firing rate) in 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 comes and load would be scarified to maintain/restore the throttle steam Pr.

BOILER FOLLOW MODE

P

+B

-

PR.

PIDFUEL FIRING DEVICE

PI

T

G MW F F

+MW SET PT.

-

U

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 fuel master(FM) output and making feeder speed controller error zero. 3. Vary Blr. Master O/P so that FM error becomes zero. Then put FM 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 to boiler follow occurs under following condition :turbine goes to manual because of any reason or operator action Pr CMC - Pr Lim > 60MW

TURBINE FOLLOW MODE: 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 Pre. Varies the opening of MSCV to maintain the set throttle steam Pre.

TURBINE FOLLOW MODE

PR. SET PT.

P

B

+PI

MW SET PT.FUEL FIRING DEVICE

T

G N

+PI

-

F

-

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 from LMT mode by itself. 5. Now load set point can be changed by varying the boiler master manually.

Unit Target Load

+

+

Freq. Deviation correction Boiler Turbine

CMC LOOP basicRunback

Min

Logic Unit Load Capability Load Rate (Set) Permissive Load Rate form turbine stress evaluator (ESE)

Min Tracking integrator

Guidance load signal

+PID

+Boiler Controller Throttle Pr. error

PR.CORRECTION CKT.

+P

TURBINE CONT.

-

+Pressure Set Signal PI Turbine Controller

Steam PR. BOILER GEN MW

CMC controls the plant treating boiler and turbine as a unit. It aims is to generate desired MW O/P through coordinate regulation of boiler I/P & O/P (turbine I/P). Turbine must not increase load without taking firing /boiler inertia in consideration. CMC coordinate sensitive turbine & slow response boiler & Auxiliaries. IN CMC Boiler master on Auto Turbine master on Auto Unit master - Receiving load demand from ALDC or Manually from desk. In cmc sets the MW set point which will be pursued by boiler master by taking throttle pressure error as final trimming input signal. Turbine will control the MW by taking mw error as input. Th.pre. 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 respond will be slow when compared to turbine response. So it may be reemphasized that this mode of operation gives maximum stability to the units with optimum response taking boiler & turbine as a unit. Pressure correction curve is basically a bridge between the slow boiler & fast responding turbine control. Performance of CMC largely depends on the proper tuning of the curve. Tuning of the curve varies with boiler & fuel .

Pressure Correction in CMCUnder 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 to frequency 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 Note: Note:THROTTLE PRESSURE (DP) correction starts at +/- 1Kg and acts upto +/- 2Kg. It will add or subtract +/- 15 MW to the GNI output, thereby generating pressure corrected GNI output to EHC.

15MW 2 Kg - DP 15MW 1 Kg 1 Kg 2 Kg + DP

FREQUENCY INFULENCE ON CMCK FMin Unit Master Max Min n M I N 1.5 % O/p + +

GNI P+ --

Frequency & Pr. Connected GNI O/P to EHC

Adder

Pre. CorrectionM A X

+ +Adder

DelayFrequency connected GNI O/P Th.Pre. Set.Pre

P

MW

F/F Boiler master PI+D 3012

10 MW

3992

20 MW

Air master master

Fuel

Frequency influence LDCUnit Master M I N

M A X

+ + -

P

Turbine load limiter CM C TFM BFM

UNIT CapabilityM I N Target of unit M I N

UNIT load rate

LOAD UNIT

MAX

MAX MIN

UNIT COORDINATER GNI

TSE upper margin

Runback limitM A X M I N

MIN LIMITING BLOCK

Actual MW Boiler demand

TFM

+P

+ D action Del ayBLI BFM Set.Pre Th.Pre

TSE lower margin PR (CMC set Pt to turbine)

BFM

+ PCMC

P

F(x)

PULV A -J PA FAN A PA FAN BM I N

PRTD

F/D TFM

Capability + Runback in action

+

+

-

Boiler master PI+D

load

CMC LOOP ST#II KORBA

Air master master

Fuel

Max

Min

Load Setter

Max / Min. Limiter TSE Influence

EHC

+

+

(Load

f)

+ +

Load Reference

+ +

GNILoad

+25MW 0. 2HZ 0. 125 HZ 40MW

+ + Delay Throttle Pressure Set. +

M I N

+

Freq

Load Limiter Pressure Correction Frequency Unloading Characteristic

Load controlle r

+ +

Actual Pressure Frequency Influence ON

Boiler Master

CMC LOOP

TOTAL COAL FLOW

28.6% 85.7% BTOTAL OIL FLOW X001 XM03Y1

XP01Y2

X

Y

P

+

PT3 A B 3X1.01

X001

A

P

+MW GENERATED

Y2 Y1

B/M O/P

AIR

+XP01

+PMIN

CV CORRECTED COAL FLOW

FUEL MASTER

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 when coal is good the effect is limited to 85% to 100% of actual coal flow

CV CORRECTION LOOPA B J

TOTAL FUEL FLOW

BOILER DEMAND

Max

XN01XN01

AIR MASTER LOOPMax PIRL

TOTAL AIR FLOW

P

XP01

HK7715D Y W

RS04 OXYGEN MASTER

Ui 80%+ +

20% Ua = Ui E

(E = 0..1)

XM02

XN01

Max XN01TOTAL AIR FLOWMIN AIR FLOW

AIR MASTER

+

AIR FLOW DEMAND

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 [Presently]

FDA

FDB

O2 TRIM -

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 is compared 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.

SELECTION OF CMC 1. Put air control on auto (at least one FD fan) 2. Put feeders speed control on auto after varying fuel master(FM) output and making feeder speed controller error zero. 3. Vary Blr. Master O/P so that FM error becomes zero. Then put FM 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 becomes equal to actual load. (wait unit load set value and load value matches as shown in the CMC panel digital indicator). 7. Form TG desk put turbine control on auto. 8. Press coordinated push button along with manual release on CMC desk.

FEED RATE

CURVE GENERATOR Generator UCB Set Point

Max Mill PA Flow

+Controller

-

HADMILL PA FLOW GENERATION CURVE

CURVE GENERATOR SETTINGS XU01 CARDHAD SET POINT FOR PA FLOW AS PER FEED RATE

FEED RATE (T/H) 0 17.5 20 30 40 50 60 70

MILL PA FLOW SETPOINT (T/H) 70 75 77 92.5 96.5 100 105 108

CURVE140

ENERATOR ETTING

120108 105

A FLOW ETPOINT(T/ )

100100 96.5 92.5

8077 75 70

60

I

40

20

0 0 17.5 20 30 40 50 60 70

FEED RATE(T/ )

TOTAL FUEL FLOW

~MAX P MAXA /M

A/M

PA FLOW FROM MILLS ANY 6 MILLS

MAXRS04

O2 -

FLUE GAS O2

O2 -

SEC. AIR FLOW (L) SEC. AIR FLOW (R)

A B C J

D E

AW02 AW

MW AIR FLOW

PI RL OOO80 % 20 %

/n

+

+( = 0.1) Ua= Ui X

TOTAL AIR

+

+

-

-

P

+

+

GAIN CHANGE

PI RL Y

AIR FLOW CONTROL SCHEME ( EXCESS AIR)PI

-

+ +PI RL

-

+

Y Act

Y

OOO

RL Y Y Act

OOO

+AW02

+P+ + AW02

-

-

-