TOPICS OF DISCUSSION

CONCEPT OF GOVERNING SYSTEM FEATURES OF KWU GOVERNING SYSTEM OVERVIEW OF GOVERNING RACK FUNCTIONING OF EHC CIRCUITS FREE GOVERNOR MODE OPERATION BEST PRACTICES IN GOVERNING SYSTEM EMERGENCIES IN GOVERNING SYSTEM ANY OTHER ISSUES

WHAT IS GOVERNING SYSTEM ?

Turbine Governing system is meant for regulation of turbine speed under no load and varying load condition.

It helps in precise control of grid frequency under normal operation and protects the machine as well as grid during emergency situation.

KWU GOVERNING SYSTEM-FEATURES ELECTRO-HYDRAULIC GOVERNING SYSTEM WITH

HYDRAULIC BACKUP OPENING OF STOP VALVES BY STARTING & LOAD

LIMITING DEVICE (HYDRAULIC) ROLLING, SYNCHRONIZATION & LOAD OPERATION

BY HYDRAULIC / ELECTRO- HYDRAULIC SYSTEM ELECTRO- HYDRAULIC SPEED GOVERNOR WITH

HYDRAULIC BACK UP SAFE SHUTDOWN BY HYDRAULIC / ELECTRO-

HYDRAULIC SYSTEM ELECTRICAL AND HYDRAULIC PROTECTION SYSTEM

ALONG WITH TEST FACILITIES

HYDRAULIC CONVERTER

FEATURES OF EHC AUTO ROLLING & SYNCHRONIZATION THROUGH

SPEED CONTROLLER UNDER INFLUENCE OF TSE CONSTANT LOAD OPERATION BY LOAD CONTR.

WITH PRESSURE CONTR. AS BACKUP RUNBACK OPERATION THROUGH PRESSURE CONTR. EMERGENCY OPERATION THROUGH SPEED CONTR. AUTO GRID FREQUENCY CONTROL THROUGH

EXTERNAL FREQUENCY INFLUENCE AUTO UNLOADING AT HIGH FREQUENCY THROUGH

INTERNAL FREQUENCY INFLUENCE CONTROL DURING AUTOMATIC TURBINE TESTING, ISOLATED GRID CONDITION & LSR OPERATION

SPEED CONTROLLER CIRCUIT

STOPGRD

FAST

DELAY ELEMENT

4

6

6

6

2

3

5

1

MV3

NLC

SPEED CONTROLLER

+

-

+

Speed signal (0 to 3600 RPM ~ 0 to 10 .8 v)

hrnc (+ 10.0 v)

nr limit

n act

0.0 V

10.0 VMINIMUM OF

UPPER STRESS MARGIN

nr

+-

TRACKING CIRCUIT

n act – 120 RPM

n act + 21 RPM

M

SETTER

R

L

NLC

DRUM PRESSURE

SP

EE

D

CO

NT

RO

LLE

R O

/P

R & L – Raise & Lower command from UCB :

nr – Speed Reference :

nr limit – Delayed Speed Reference :

NLC – No Load Correction (Ensures required Speed controller O/P for Rolling even when Speed

reference n r matches n act.)

n act – Actual Speed :

hr nc – Speed Controller O/P with DROOP of + / - 10.0 V for nr lim ~ n act = 150 RPM ( GAIN = 22)

Logic1

Sigma Pr

GRD

FAST

DELAY ELEMENT

5

M

SETTER

R

L

6

CMC RUNBACK

2

ep

1

CMC

OR

Frequency signal

STOP

7

+-

SETTER

R

L

MIN

+/- 10 V

3

Upper & Lower Stress Margin

MIN

+/- 10 V

4

DP/Dt SETTER

R

L

Pr delta f

Pr limit

Pr MAX

Pr

R – Raise command

L– Lower command

Pr – Load set point

Pr lim – Delayed load set point

Pr max – Load limit

Sigma Pr – Final Load set point

DP / Dt – Load gradient

Pr delta f – External frequency influenced Load reference

Ep – Megawatt error (Pr ~ P actual)

1 – SET POINT FOLLOW UP when Automatic Grid Control or CMC In service

(Other Raise / Lower commands get blocked)

2 -- TSE ENABLING when

A) GCB is closed AND

B) Load controller (L C) not OFF AND

C) Fast calibration signal 6 absent AND

D) I) Load controller (L C) in control

OR ii) Pressure controller with initial pressure in action

OR iii) Turbine follow mode in service

This helps to bring manually adjusted gradient and stress effect in service.

+/- 10 V gradient => +/- 25 MW / MIN for 200 MW units

OR +/- 50 MW / MIN for 500 MW units.

LOAD SET POINT GENERATION CIRCUIT

Logic2

LOAD CONTROLLER CIRCUIT

TO TRANSFER CKT ONLY

8

+ 1 V

-

+

-

+

hr Pc

hr nc

hr minhr Prc

h V0

h Vu

+ 50

+ 0.1

+1

Gains

- 10 V

9

hr Pc

(+/- 10 V)

+

-

-

+

5 % DROOP

Frequency Signal

Pr

P act (0 – 10 V)

MV 3

LOAD SIGNALS

100 % Load Set point

Pr

f (f + 2.5) HzFrequency

Unloading Droop (5%)

P act -- Actual load

-- Final Load set point

Hr Pc -- Load controller output

Hr Prc -- Pressure controller output

Hrnc -- Speed controller output

Hr min -- Selected output from Speed & load controller

Pr

Logic3

PRESSURE CONTROLLER CIRCUIT

Actual Pressure ( 0-250 BAR ), Pact ( 0-10V )

Pr ( 0-10V ) hr Pr c ( +4V to + 10 V )

Set Pressure ( 0- 250 BAR )-

+

+ 1

+ 0.1Gain

4V ( Lower limit )

0.4 V (10 BAR)

Initial Pressure Mode

Lower limit of 4V (adjustable) does not allow the Pressure controller output (hr Prc) to come to very low value; interference with Speed controller is also avoided.

Addition of 0.4 V in limit pressure mode helps to saturate Pressure controller output when Load controller is brought in service. This also helps to bring Pressure controller in service when Pressure drops 10 ksc from set point in Load controller mode.

O S C – Over Speed Channel for m/c unloading when frequency increases above the limit of speed reference tracking

hr min – Selected o/p from Speed & Load controller

hr- Final controller output (EHC output)

Collins feedback - Position of ElectrohydraulicAmplifier Piston(Governing Rack)

P/A – Position / Admission controller

ha – Admission controller output

M

A

X

+

+

M

I

N

M

I

N+

+

M

I

N

hrnc

hrpc

+10 vO S C

hrprc

hrhr min

0 to 10 v

COLLINS 1 FEEDBACK

COLLINS 1 FEEDBACK 0 to -10 v

DESK INDICATION (EHC FEEDBACK)

P/A

ha

PLUNGER COIL ON

EHC PLUNGER COIL

B

B - Electronic card which produces balance voltage for EHC plunger coil, which is ideally adjusted = -1.0 v

EHC TRANSFER CIRCUIT

FGMO – BACKGROUND Unique frequency band of 49.0 Hz to 50.5 Hz, as

specified by IEGC Scheduling & dispatch by RLDCs/SLDCs is based on

day ahead demand & availability Frequency control by load-generation balance in every

15 mins time block Wide frequency variation during Grid disturbance,

Unit outage, change in demand, etc. No primary response by generators to maintain

frequency under such system contingency Emergencies caused due to frequency control only

through importing /cutting load by system operator

FGMO – GRID CODES All generating units should have their speed governors

in normal operation at all times to enable Grid frequency control by loading / unloading

Droop characteristic for primary response should be within 3% to 6%

Each unit shall be capable of instantaneously picking up at least 5% extra load for a minimum of 5 mins (up to 105%MCR), during fall in frequency

No dead bands and/or time delays shall be deliberately introduced

Facilities like load limiters, CMC, etc. shall not be used to suppress the normal governor action

IMPLEMENTATION OF FGMO In line with clause Clause 1.6 of IEGC and CERC

order dated 30-10-99, date of FGMO implementation, as decided by REBs are :-

Western Region - 19-05-03 ( ABT – 01-07-02 ) Southern Region - 01-08-03 ( ABT – 01-01-03 ) Northern Region - 01-10-03 ( ABT – 01-12-02 ) Nor-East Region - 22-12-03 ( ABT – 01-11-03 ) Eastern Region – 02-01-04 ( ABT – 01-04-03 )

FGMO CHARACTERISTIC FOR KWU M/C

.

MW

49.00 49.62550.375

50.50

Hz.52.625

-500 (-200)

+75 (+30)

-75 (-30)

+200 (+80)

-100(-40)

52.50

5% DROOP (± 2.5Hz.)

0.5 Hz. = 100MW (40)

0.1 Hz. = 20MW (8)

Manufac.Setting

Changed Setting

50.00

(+)

(-)

UNIT RESPONSE UNDER FGMO

MAJOR ISSUES EVOLVEDWide and frequent variation of freq.

Perpetual oscillations in critical parameters due to Boiler response time

M/C subjected to cyclic loading and fatigue stresses

Frequent HP/LP Bypass valve operation

Continuous manual interventions

Self-defeating feature(Unloading when freq. improving towards 50 Hz)

Conflict with ABT(Offsetting freq. correction)

MODIFIED FGMO SCHEME

Technical committee constituted by CEA submitted report to CERC in Nov,04

Subsequently the Member(Thermal) suggested few changes

Modified scheme implemented in CMC circuit and tested in Simhadri in Dec,04

All NTPC coal stations are directed to implement the modified scheme

MODIFIED FGMO - OBJECTIVES Frequency Droop of 5% to 10% (49HZ TO 50.5HZ) Floating frequency set point with tracking of frequency @

0.02 Hz/min Deletion of holding circuit Limited response of + 5% within frequency range of

49.0Hz to 50.5Hz Above 50.5Hz, load reduction can be 10% up to technical

minimum Deletion of feed forward signal to Boiler Preferred mode without varying fuel to Boiler Parametric variation within + 1% with tuning

IMPLEMENTATION IN EHC PANEL

R12

R 11

D18

X21

AFU 12

BL 051

D2

D4

D8

D6

X21

Z14 (-15V)

Z10 D18

X24

X25

AVB 11.3

AVB 11.4

AVB 11.2

B20D22

Z14(-15V)

BE 163

AVB 11 (LIMITER MODULE)

D14

D26

BH 107

AFZ 11

(RAMP

GENERATOR)

AFZ 11.1

X12

B4 (+)

B22 (-)

D22

BP 035

AVG 11.1

X14

D22 (+)

B24 (-)

D6

AVG 11.2

X24

X22

B6

R13Z8

B14(+15V)

AVG 11.6

AVG 11 (COMPARATOR)

D22 (+) X24

BH 027

AVG 11

BL 059

X11

(-)

AFL 11

n act

f 0

DROOP

( 8 % )

Wiring

UNIT RESPONSE UNDER MODIFIED FGMO

BEST PRACTICES IN POWER SYSTEM Replacement of critical fuses of power supply panels

during each overhauling Load testing of ATRS power packs(AKS11) Checking and replacement of failure-prone capacitors of

ATRS cards Checking of healthiness of system ground connections and

reference potential Checking of ATRS panel bus terminal tightness Regular monitoring of healthiness of ATRS power supply

systems Ensuring voltage level within 10% above rated voltage at

ATRS panel end

BEST PRACTICES IN CONTROL SYSTEM Checking of EHC and TSE card settings during

overhauling Adjustment of Plunger coil balance voltage and

Collins feedback Cleaning of pilot valves of HP/IP control valves Cleaning of Duplex and Simplex Plate filters of

Governing Rack Checking of EHC and Hydraulic Governing

characteristics with Tracking OFF and ON condition and control valves calibration checking

BEST PRACTICES IN OPERATION PHYSICAL INSPECTION OF VALVE ROOM AND

GOVERNING RACK AUTO ROLLING AND SYNCHRONISATION(SGC) PERIODIC CHECKING OF TRIP DEVICES(ATT) DAILY ROTATION OF DUPLEX & SIMPLEX

FILTERS IN GOVERNING RACK PERIODIC CHECKING OF AVAILABILITY OF

AOP AND JOP DAILY CHECKING OF AVAILABILITY OF EOP EMERGECY HANDLING THROUGH LAID DOWN

PROCEDURE

EMERGENCY IN GOVERNING SYSTEM

FAILURE OF POWER PACKS OF CONTROLLER RACKS IN EHC PANEL

POWER SUPPLY FAILURE IN ATRS PANEL SIGNAL ACQUISITION PROBLEM FAILURE IN TURBINE SYSTEM ELECTRICAL SYSTEM FAILURE COMPONENT FAILURE IN GOVERNING

RACK OPERATIONAL EMERGENCY

M/C is on EHC. Power supply fails in Load control/Pressure control / transfer circuit rack. Starting device becomes off automatically due to EHC fault.

Observation: EHC output is minimum/zero and load minimum/ zero with EHC fault alarm. Machine on bar with ESV & IV open (Turbine not tripped).

Action: Confirm HP/LP bypass opening, isolate EHC from governing rack and parallely adjust starting device position from UCB. Reduce boiler firing to restrict rise in boiler pressure.

CONTROL RACK SUPPLY FAILURE

SUPPLY FAILURE IN ATRS PANEL M/C is on EHC. Power supply fails in CCA panels

only. Observation: All indication lamps in ATRS consoles

will go off. EHC output and Load will become zero due loss of GCB close feedback. All ATRS drives will become inoperative.

Action: Confirm HP/LP bypass opening , isolate EHC. Reduce boiler firing. Adjust starting device position from local. Normalize power supply in CCA panels at the earliest.

SIGNAL ACQUISITION PROBLEM Loss of speed signal occurs due to Hall Probe /

card failure.Observation: Speed indication will become zero.

M/C will be loaded through speed controller. Subsequently Pressure controller will come in service. AOP & JOP will take auto start & Barring Gear valve Will open on auto.

Action: Isolate EHC and adjust Starting device position. If pressure oil pressure is normal, make SLC of AOP, JOP and Barring Gear vlv OFF and stop AOP, JOP and close Barring Gear vlv.

FAILURE IN TURBINE SYSTEM Loss of speed signal occurs due to breakage of

MOP shaft.

Observation: Speed indication and pressure oil pressure will come down. M/C will be loaded through speed controller and Pressure controller will come in service. Subsequently, AOP & JOP will take auto start &Barring Gear valve. will open on auto.

Action: Safe shutdown of M/C is to be ensured.

ELECTRICAL SYSTEM FAILURE M/C is on EHC with Tracking on. Starting device

becomes inoperative due to Electrical module trouble/motor failure/overload.

Observation: During increase in boiler firing, Boiler pressure will increase due to load restriction by Starting device. EHC output will go to 100%.

Action: Switch off the electrical module of Starting device and increase Starting device position from local so that EHC can take control.

FAILURE IN GOVRRNING RACK

EHC Plunger coil failure EHC Pilot valve bearing failure

Observation: EHC starts hunting

Action: Isolate EHC and take Hydraulic mode in service. Replace the failed omponent. Governing characteristic checking should be done before EHC is put in service

FAILURE IN GOVRRNING RACK

Speeder Gear spring tension gets altered.

Observation: M/C may get unloaded at frequency lower than recommended value.

Action: Speeder Gear spring tension may be adjusted to increase the start of unloading.Testing for proper setting should be checked during suitable opportunity.

OPERATIONAL EMERGENCY

M/C is just synchronized in Speed control mode and changed over to Load controller. Load above block load is not stabilized due to low drum pressure operation.

Observation: EHC will get saturated(100%). Load controller may changeover to speed controller when M/C will be unloaded.

Action: Isolate EHC.Stabilize load in Hydraulic mode and then put EHC in service

OPERATIONAL EMERGENCY

M/C is on EHC. Unloading takes place due to restriction by TSE margin.

Observation: TSE indicator will show abnormal margins and load will come down.  Speed controller will be active if load comes below 10%(block load).

Action: Isolate EHC to take M/C on Hydraulic mode. Decrease load for stabilization.

 

SPEED CONTROLLER LOGICS

1 Command for slow rate at nr > 2850 RPM to facilitate easy synchronisation

2 TSE Influence ON, when min of all the upper stress margins comes into picture to control gradient of nr lim and hence, acceleration of Rolling speed. Upper stress margin = 30 deg C => 10.0 V => 600 RPM ~ (Acceleration < 108 RPM ~ causes dn / dt tripping)

3 Stopping of nr lim when

a) GCB open AND

b) n act is < nr lim by approx. 45 RPM.

This restricts hr nc up to around 30 % during Rolling to avoid wide v/v opening.

4 Stopping speed set point control when,

a) n act > 2850 RPM AND

b) nr raised ( I.e, nr > nr lim) AND

c) I) TSE ON and faulted in GCB open condition

OR ii) Stop command from SGC in SGC ON condition.

SPEED CONTROLLER LOGICS5 Tracking in synchronized condition if

a) Frequency within limit (adjustable, say 48.5 to 51.5 Hz.) AND

b) Load controller O/P , hr pc > hr nc AND

c) I) Load controller (L C) in control

OR ii)Pressure controller in action

6 Set Point Follow Up (Fast Calibration) during

a) Tracking condition 5 ( nr = n act + 21 RPM ) OR

b) Turbine Trip ( nr = n act – 120 RPM ). Simultaneously nr lim immediately equals to nr

Condition (a) ensures certain speed controller O/P during emergency to keep machine in rolled condition along with some load.

Condition (b) ensures negative speed controller O/P during Trip condition.

LOAD CONTROLLER (L C) IN CONTROL CONDITIONS –

a) Speed OR Pressure Controller not in action AND

b) Isolated Grid condition absent AND

c) Both Load Controller OFF and Schedule OFF absent (I.e, L C ON)

LOAD CONTROLLER SCHEDULE OFF – L C can be made OFF if Speed controller is in action and hrnc > hr pc. Otherwise, with OFF command OFF lamp blinks – called Schedule OFF

Back

LOAD SET POINT GENERATION LOGICS3 -- TSE ON AND NOT FAULTED

This helps to keep stress effect for gradient control in service.

4 -- LOAD GRADIENT ON

This helps to keep manual gradient control in service

5 -- STOP POWER SET POINT CONTROL when

a) TSE ON and Faulted OR

b) Stop command from SGC OR

c) Pr raised when Pressure controller is in action with CMC ON OR Limit pressure mode selected OR Boiler follow mode selected

In above conditions Pr lim stops, I.e,Set point can not be increased.

6 -- FAST CALIBRATION when

a) Pressure controller is in action OR

b) Follow above (h v0) condition present

Under this condition MW error (ep) is selected and Pr lim immediately equals to Actual load (P act) without any gradient .

7 -- FREQUENCY INFLUENCE ON

This is made ON from ATRS panel to put EXTERNAL FREQUENCY EFFECT in service for

loading / unloading w.r.t. 50 Hz ( with 2.5 % to 8 % Frequency Droop)

TSE TEST RELEASE : TSE TEST (For checking healthiness of TSE Margins) can be done when

a) TSE Influence is OFF OR

b) Both Pr, Pr lim and hr, hr lim are balanced, I.e, Speed and Power set point controls are not in action.

Back

LOAD CONTROLLER LOGICS

FOLLOW ABOVE ( h v0 ) --

a) GCB closed and load < 10 % (station load) OR

b) GCB open OR

c) Load controller OFF

Absence of these conditions help Load controller output to track above Pressure controller output when Pressure controller is in service.

FOLLOW LOW ( h vu ) – GCB CLOSED AND Speed controller in action.

This helps Load controller output to track below Speed controller output.

8 -- Either a) Initial pressure mode selected OR

b) Turbine follow mode in action OR

c) CMC Runback active

This ensures Load controller output above pressure controller output

9 -- Load controller OFF

This defeats transmission of Load Controller output to Transfer circuit.

Back

MODIFIED FGMO WIRINGIMPLEMENTATION IN: ATRS PANEL ( CJJ02 )

CARDS USED: 1) LIMITER MODULE AVB 11 AT LOCATION BE 163 SPARE CHANNELS - 2,3,4  2) RAMP MODULE AFZ 11 AT LOCATION BH 107 SPARE CHANNEL - 1   3) COMPARATOR MODULE AVG 11 AT LOCATION BP 035 SPARE CHANNEL – 1,2,6 WIRING DETAILS: REMOVE: BL 051-D18 TO BH 027-D22 CONNECT: BE 163-D4 TO BE 163 -D18 BE 163-D8 TO BE 163- B20 BE 163-Z14 TO BE 163 -Z10 BE 163-Z14 TO BE 163 -D22 BE 163-D6 TO BH 107-D14 BE 163-D6 TO BP 035-B4 BH 107-D26 TO BP 035-B22 BP 035-D20 TO BP 035-D22 BP 035-B24 TO BP 035-B6 BP 035-B14 TO BP 035-Z8 BP 035-D6 TO BH 027-D22 BL 051-D18 TO BE 163-D2

MODIFIED FGMO SETTINGS 1 1)  SPEED INPUT: MEASURE 0 TO –10V AT BL 051-X21 FOR INPUT 2800 RPM TO 3200

RPM2 2)      LIMITER (49 HZ TO 50.5 HZ): MAKE S 2.1 ON AND S 2.4 ON IN AVB 11(BE 163) SET - 3.5 V AT BE163-X25 BY R12 (49 HZ) SET - 5.7 V AT BE163-X24 BY R11 (50.5 HZ) CONFIRM LIMITATION AT BE163-X213 3)      FREQ. RAMP (0.04HZ/MIN/): MAKE S 2.3 ON, S 3 OFF AND S 4 OFF IN AFZ 11(BH 107) SET 30mV/MIN(FOR 0.02 HZ/MIN) AT BH 107-X12 BY -- R12 FOR UPWARD & R13 FOR DOWNWARD RAMP) 4)   COMPARATOR (FREQ. DEVIATION): MEASURE FREQ. DEVIATION AT BP 035-X14 SET + 5 V AT BP 035-X22 BY R13 MEASURE 0 TO –10V AT BP 035-X245 5)    DROOP (WITH + 5% RESPONSE): MEASURE FULL RESPONSE AT BH 027-X24 SET 8% DROOP AT BL 059 SET + 0.415V(FOR + 5% RESPONSE )AT BL 059-X11 BY R13 FOR UNLOADING & R14 FOR LOADING

Back