FGMO

Restricted Governing Mode of Operation

Free Governing Mode of Operation (FGMO)

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 and Wide frequency variation during Grid disturbance, Unit outage, Change in

demand, etc.

 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

FGMO SMOOTHEN THE WIDE FREQUENCY FLUCTUATION

FREQUENCY COMPARISION

48.0

48.5

49.0

49.5

50.0

50.5

51.0

51.5

52.0

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12 21:36 0:00

TIME

F R EQ U E N C Y

26/1/04

26/1/03

Source:ERLDC Website

PRE ABT REGIME WITHOUT FGMO

POST ABT REGIME WITH

MAJOR ISSUES WITH FGMO IN 2004

• Perpetual oscillations in critical parameters

• M/C subjected to cyclic loading and fatigue

stresses

• Frequent HP/LP Bypass valve operation

• Continuous manual interventions

• Self-defeating feature (Unloading when freq.

What is RGMO ?

Frequency profiles of power system in India has improved

significantly after implementation of ABT and the same is now

generally remains with in 49 to 50.5 Hz against pre ABT levels of 47.5

to 52.5 Hz.

The response of Governors as a first line frequency control

mechanism is practiced internationally. How ever the frequency

variations will normally be +/-0.1% to 0.2% in those countries.

Hence for our country CEA has proposed a moderated from of

CERC Order

Hon’ble CERC,vide order dated 20.08.09 has issued directions for

implementing the RGMO,relevant extracts of which are

furnished here below.

Quote:

39.In the present scenario of deficit, it is not desirable to have any

frequency response from generators by reducing generation

when frequency is rising towards 50 Hz from a lower level.

Reduction of generation would be necessary when frequency is

already above 50 Hz and tends to rise further. Therefore

suitable control logic would have to be developed to limit the

governor response to situations when frequency is rising and

grid frequency is below 50 Hz. Such a situation could be

called a restricted governor mode of operation and not total

FGMO. How ever this does not exempt the generators from

getting the free governor mode in to operational state for use

when required.

Salient features of the CERC Order

 Load change is proposed to be limited to +/-5% of MCR in

the frequency range of 49 Hz & 50.5 Hz and sustained for

about 5 minutes before ramping back to original load

automatically.

 Small changes up to +/- 0.03Hz are ignored for load

corrections.

 For frequency below 49 Hz and above 50.5 Hz,5% droop of

the governor would be effective with load change limited to

+5% of MCR for frequency below 49 Hz and -10% of MCR

above 50.5 Hz.”

Chronology of Events

Sl No. Date Event

1 20.08.2009 CERC has given an Order dated 20.08.2009 for implementation of RGMO

2 01.03.2010 Scheduled date for putting the new scheme in to service for Thermal Sets 200 MW and above for Software

based EHG Control System.

3 01.06.2010 Scheduled date for putting the new scheme in to service for Thermal Sets 200 MW and above for Hardware

based EHG Control System

4 16.02.2010 Scheduled trail implementation of RGMO in Eastern Region

OS Recommendations on RGMO

For machines with Hydraulic Governing,

the Control logic for restricted governor mode of operation will

be as follows

1. If frequency < 50 Hz, any decrease in frequency will result

in increase in generation by Governor action as per

droop(4-5%)

2. If the frequency < 50 Hz, any increase in frequency up to 50

Hz will result in no action.

3. If frequency > 50 Hz, any increase in frequency will be reset

by a slow automatic resetting command to ramp back to

MW set point @ 1% per minute.

4. A dead time of 5 to 15 minutes (Variable setting) will be

provided before the next governor action is allowed.

5. The quantum of load change may be restricted to +/-5%

from the original level.

NTPC Kaniha comments and action plan given to OS

Sl

No

IOM Ref No OS/CC/FGMO/09

For Machines with EHG –Control Logic for Restricted mode of Operation

COMMENT

i) If frequency < 50 Hz, any decrease in frequency will result in increase in Generation by Governor Action as per droop (4%-5%)

This is possible to be implemented with 5% droop. In fact this is available in the existing logic of FGMO with a droop of 10%.

ii) If frequency < 50 Hz, any increase in frequency up to 50Hz will result in NO Action.

This Logic modification is possible. To be implemented.

iii) If frequency >50 Hz, any increase in frequency will result in decrease in Generation by Governor Action as per droop (4%-5%)

This is possible to be implemented with 5% droop. In fact this is available in the existing logic of FGMO with a droop of 10%.

iv) The increased / decreased generation will be reset by a slow automatic resetting command to ramp back to MW set point @ 1% per minute.

This is possible to be implemented.

v) A dead time of 5 to 15 minutes (variable setting) will be provided before the next governor action is allowed.

NTPC Kaniha comments and action plan given to OS

Sl

No

IOM Ref No OS/CC/FGMO/09

For Machines with EHG –Control Logic for Restricted mode of Operation

COMMENT

vi) _{IMPLEMENTAION SCHEDULE:}

The implementation of the suggested logic vide IOM OS/CC/FGMO/09 will be implemented after getting approval from CC-OS/Engg.

However, it can be carried out during Opportunity Shutdown / Overhauling.

ii) _{TSTPS_Stage-I Units (2X500 MW)}

In stage-I, the TG sets are of ABB make and Electro Hydraulic Governing is also of ABB make. The existing scheme is enclosed. Since the CERC order specifies only for KWU & LMZ turbines, applicability of the same for ABB turbine may be clarified. If applicable, the same

scheme can be implemented after consultation with OEM (M/S ABB,

Approval from Engg./ OS

NTPC Ltd.

Talcher Supper Thermal Power Project.

INTER OFFICE MEMO

From: DGM(O&M/C&I) To:1.AGM(OS/C&I)

2. HOD( PE/C&I) EOC, NOIDA Ref: 9501/O&M/C&I/ CC: 1.ED (TK): for kind inf. pl.

2. GM (O&M): for kind inf. pl. 3. AGM (M): for kind inf. pl. Date: 13-11-2009.

Sub: Implementation of restricted governing mode of operation; draft logic proposal for approval reg.

With reference to above subject and IOM: OS/CC/FGMO/09 dated: Sept-10-2009, please find enclosed the modified logic for implementing restricted governing mode of operation. Approval from OS / Engineering is sought for the proposed scheme to enable us to implement the same at our site as per the schedule. For point no IV and V we have faced difficulty in proposing the scheme, this may be taken care while finalizing the logic.

Since our system falls under the category of “Software based EHG system” we need to implement the same after taking all necessary approvals before 31/03/2010. This also needs unit shutdown for implementation. Early finalization and approval will enable us to implement the same with in schedule.

-500 -475 -450 -425 -400 -375 -350 -325 -300 -275 -250 -225 -200 -175 -150 -125 -100 -75 -50 -25 0 25 50 49.65 50 50.55 51.1 51.65 52.2 Frequency In Hz L o a d I n c /D e c i n M W 5 % Droop 50.15

Frequency dead band will be off automatically if: 1) Frequency Deviation is +/-1Hz.

2) Rate of Change of Frequency is greater than 25 rpm/sec

There is no Hydraulic Governor in Main Turbine.The Droop characteristics implemented in EHC.

49.85 52.65

49.725

Modified scheme in Talcher Kaniha Stage-I (2X500MW)

FKG 0% = 0% 81.739% (2820rpm) = 0% 86.956% (3000rpm) = 50% 92.173% (3180rpm) = 100% Speed Signal in 0-100% Range (0 – 3450 rpm) SWI P001=10% E P002=112 s ABG TY2=0 s OG =58.33 %( 50.5Hz) UG =33.33% (49 Hz) Tracking @0.02Hz/Minute

Scaling the frequency from 47.0 Hz to 53 Hz. SMU + K=1 - BEG OG = 50.5 % UG = 49.5% MOK – K 2 Seconds BEG OG = 58.33 % UG = 38.33% ODR ODR If frequency is between 50.03 Hz to 49.97Hz, then O/P follows I/P.

When Load mode is „ON‟, then O/P will be made equal to I/P by a 2 second pulse.

Load Mode on Shot

„1‟ if f>50.03Hz „1‟ if f<49.97Hz

Finds the difference between Tracking frequency O/P and the actual frequency.

UMS MAX FIX 0% MIN FIX 0% Ensuring that if frequency > 50.03 Hz only unloading is allowed. Ensuring that if frequency < 49.97 Hz only loading is allowed.

BEG OG= +0.49% UG= -0.49% SMU + P006 =0.122 - SMU P003=16.66 BEG OG= +5% UG= -10% Droop = 6%=2.77MW/RPM P006 = 0.12 P003 = 16.66 Range converted from 47-53Hz to 0-50 Hz

Switching between New Scheme & Old scheme

SWI E1 GRD=100% TY1=P005= 3 Min ABG OG = + 100 % UG = - 100% UMS UMS TBT R Q S UND

Switching between old scheme and new scheme depending on the grid frequency

If Freq > 50.5Hz, SWI output is old

f will be Final output.

GOG OG = 58.33% P004 = HYS = 3.3% Speed corrected ADS + - GUG P007 = G = 2% HYS = 0.5% ABS

Delta frequency from old scheme

New Delta Frequency

Frequency

If Freq > 50.5 Hz old delta Freq will come into service.

If Freq < 50.5 Hz, difference between old scheme O/P & new scheme O/P is

 10 MW (2%) then only new f will be direct O/P. Otherwise integrated output.

Modified scheme in Talcher Kaniha Stage-I (2X500MW)

-500 -475 -450 -425 -400 -375 -350 -325 -300 -275 -250 -225 -200 -175 -150 -125 -100 -75 -50 -25 0 25 50 49.65 50 50.55 51.1 51.65 52.2 Frequency In Hz L o a d I n c /D e c i n M W 6 % Droop 50.15

Frequency dead band will be off automatically if: 1) Frequency Deviation is +/-1Hz.

2) Rate of Change of Frequency is greater than 25 rpm/sec

There is no Hydraulic Governor in Main Turbine.The Droop characteristics implemented in EHC.

49.8 52.65

49.725

Dynamic Correction between 49 to 50.5 Hz

-525.00 -500.00 -475.00 -450.00 -425.00 -400.00 -375.00 -350.00 -325.00 -300.00 -275.00 -250.00 -225.00 -200.00 -175.00 -150.00 -125.00 -100.00 -75.00 -50.00 -25.00 0.00 25.00 50.00 75.00 100.00 49.4 49.55 49.7 49.85 50 50.15 50.3 50.45 50.6 50.75 50.9 51.05 51.2 51.35 51.5 51.65 51.8 51.95 52.1 52.25 52.4 Frequency in Hz L o a d I n c re a s e /D e c re a s e i n MW 49.65 52.50

Machine Droop

5%

Existing Scheme in Talcher Kaniha,Stage-II (4X500MW)

Dynamic Correction between 49 to 50.5 Hz

Modified scheme in Talcher Kaniha Stage-II (4X500MW)

ACTUAL SPEED F(X) 47-53 HZ TRACKING RAMP GEN TRACKING RATE 0.02 HZ/MIN LIMITER 49 -50.5HZ LIMITER 49 – 50.5 HZ - + FREQ DEVIATION SWITCHING F(X) FREQ <49 HZ OR >50.5 HZ FREQ <49 HZ OR>50.5 HZ DROOP @ 5% FREQ FILTER +/- .03 HZ LOQD LIMIT +/- 25 MW FOR 49<F>50.5 +25 MW TO -50MW FOR F<49,50.5> FREQ ON /OFF LOAD SET POINT P_RTD + + SUM OF PR PR MAX LOAD CONTR OLLER SELECT 0 LOAD<350 MW DYNAMIC FREQUENCY ERROR

M A X 0 %

S E L E C T FREQ < 50HZ ACTUAL LOAD LOAD CONTOLLER OUTPUT MIN

Difference between Old scheme & new scheme

Sl No. Old FGMO Scheme

New RGMO Scheme

1 Machine is unloaded when the

frequency raises from a lower value to 50 Hz.

This point is taken care in the RGMO scheme. No unloading will be there when frequency raises to 50 Hz.

2 Stage-I:

Frequency dead band is ±0.15 Hz. A Permanent filter of 0.05 Hz will always be effective.

Stage-II:

A Permanent filter of ± 0.03Hz will always be effective.

Frequency dead band is ±0.03 Hz.

Frequency dead band is narrowed down to ± 0.03Hz.

A Permanent filter of ± 0.03Hz will always be effective.

3 Load correction will be there irrespective of the frequency

raise/fall once the frequency dead band limits are crossed.

Correction depends on the frequency error between tracking frequency and actual frequency.

If frequency raises/falls at a slower rate of 0.02Hz/Minute i.e 1.2

rpm/Minute then there will not be any load correction irrespective of the

New RGMO Scheme ( Stage-I Vs Stage-II)

Sl No. Stage-I RGMO Scheme

Stage-II RGMO Scheme

1 There is no provision to switch

off/on the frequency influence. It is always effective.

There is a provision to switch on/off the frequency influence scheme by the Desk/C&I Shift Engineer.

2 For frequencies above 50.5 Hz, old scheme will come in to service

which unloads the machine at a droop of 6%.

For frequencies above 50.8 Hz, machine droop will come in to service.

Between 49Hz & 50.8Hz the unloading will be limited to the technical minimum of 350 MW. Between 49 Hz to 50.5 Hz

loading/unloading will be limited to +/-25 MW.

For frequencies < 49 Hz & > 50.5 Hz loading/unloading will be limited to +50 MW & -25 MW respectively.

Implementation of the new scheme

• Earlier FGMO modifications were done in Turbotrol 52 R3

processor. If any correction is to be done in the scheme, this

processor is to be removed which often becomes risky.

• In Stage-I Turbotrol Panel one new 70PR03 Processor was

installed.

• It takes the actual speed signal from the local bus and after

executing the new RGMO Logic, it will give the frequency

influence correction as another bus signal to TT52 Processor.

• This approach facilitates easy modification of the scheme in

future.

• Similar RGMO program was implemented in a Drive control

module card (83SR05) in the PROCONTROL 14 System and

the output was given in POS Operator station for parallel

Load Set Point Memorized

UMS

Gen Load delayed MW controller ON

UMS

Unit SP Turbine CMC ON

UMS

Pressure controller POS Initial Pressure Controller ON

MUL

LS Pressure SP Delayed

MIN

Fast Unload in action

SUM

Thermal Forced Unload

Turbine Speed Droop

Droop=( Speed at no load – Speed at full load) x 100% (Rated Speed)