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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

WHAT IS GOVERNING SYSTEM ?

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

n 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

n ELECTRO-HYDRAULIC GOVERNING SYSTEM WITH HYDRAULIC BACKUP

n OPERATION OF STOP VALVES BY STARTING & LOAD LIMITING DEVICE (HYDRAULIC)

n ROLLING, SYNCHRONIZATION & LOAD OPERATION BY HYDRAULIC / ELECTRO- HYDRAULIC SYSTEM

n ELECTRO- HYDRAULIC SPEED GOVERNOR WITH HYDRAULIC BACK UP

n SAFE SHUTDOWN BY HYDRAULIC / ELECTRO- HYDRAULIC SYSTEM

n ELECTRICAL AND HYDRAULIC PROTECTION SYSTEM ALONG WITH TEST FACILITIES

FEATURES OF EHC

n AUTO ROLLING & SYNCHRONIZATION THROUGH SPEED CONTROLLER UNDER INFLUENCE OF TSE

n CONSTANT LOAD OPERATION BY LOAD CONTR. WITH PRESSURE CONTR. AS BACKUP

n RUNBACK OPERATION THROUGH PRESSURE CONTR.

n EMERGENCY OPERATION THROUGH SPEED CONTR.

n AUTO GRID FREQUENCY CONTROL THROUGH EXTERNAL FREQUENCY INFLUENCE

n AUTO UNLOADING AT HIGH FREQUENCY THROUGH INTERNAL FREQUENCY INFLUENCE

n CONTROL DURING AUTOMATIC TURBINE TESTING,

ISOLATED GRID CONDITION & LSR OPERATION

SPEED CONTROLLER CIRCUIT

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

LOAD SET POINT GENERATION CIRCUIT

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.

PRESSURE CONTROLLER CIRCUIT

EHC TRANSFER CIRCUIT

FGMO - BACKGROUND

n Unique frequency band of 49.0 Hz to 50.5 Hz, as specified by IEGC

n Scheduling & dispatch by RLDCs/SLDCs is based on day ahead demand & availability

n Frequency control by load-generation balance in every 15 mins time block

n Wide frequency variation during Grid disturbance, Unit outage, change in demand, etc.

n No primary response by generators to maintain frequency under such system contingency

n Emergencies caused due to frequency control only through importing /cutting load by system operator

FGMO - GRID CODES

n All generating units should have their speed governors in normal operation at all times to enable Grid frequency control by loading / unloading

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

n 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

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

n 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 :-

n Western Region - 19-05-03 ( ABT - 01-07-02 )

n Southern Region - 01-08-03 ( ABT - 01-01-03 )

n Northern Region - 01-10-03 ( ABT - 01-12-02 )

n Nor-East Region - 22-12-03 ( ABT - 01-11-03 )

n Eastern Region - 02-01-04 ( ABT - 01-04-03 )

FGMO CHARACTERISTIC FOR KWU M/C

MAJOR ISSUES WITH FGMO IN 2004

Ø Wide and frequent variation of freq.

Ø Perpetual oscillations in critical parameters due to Boiler response time

Ø M/C subjected to cyclic loading and fatigue stresses

Ø Frequent HP/LP Bypass valve operation

Ø Continuous manual interventions

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

Ø Conflict with ABT(Offsetting freq. correction)

TRANSIENTS IN GOVERNING SYSTEM

n FAILURE OF POWER PACKS OF CONTROLLER RACKS IN EHC PANEL

n POWER SUPPLY FAILURE IN ATRS PANEL

n SIGNAL ACQUISITION PROBLEM

n FAILURE IN TURBINE SYSTEM

n ELECTRICAL SYSTEM FAILURE

n COMPONENT FAILURE IN GOVERNING RACK

n OPERATIONAL EMERGENCY

1 CONTROL RACK SUPPLY FAILURE

n 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.

2) SUPPLY FAILURE IN ATRS PANEL(ATRS=Automatic Turbine Rolling & Synchronisation)

n 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.

3) SIGNAL ACQUISITION PROBLEM

n 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.

4)FAILURE IN TURBINE SYSTEM

n 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.

5) ELECTRICAL SYSTEM FAILURE

n 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.

6) FAILURE IN GOVRRNING RACK

n EHC Plunger coil failure

n 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

n 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.

LOGICS

A 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)

B LOAD SET POINT GENERATION LOGICS

1 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.

2 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.

3 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

4 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

C .LOAD SET POINT GENERATION LOGICS

1TSE ON AND NOT FAULTED

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

2-- LOAD GRADIENT ON

This helps to keep manual gradient control in service

3-- 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.

4-- 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 .

5 -- 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)

6 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.

D .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.

R & L - Raise & Lower command from UCB :

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