system restoration procedures dec 12

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SSYYSSTTEEMMRREESSTTOORRAATTIIOONNPPRROOCCEEDDUURREESS

FFOORRNNOORRTTHHEERRNNRREEGGIIOONN

(No Copying Without NRLDC Permission)

http://www.nrldc.org

December

2012012012012222


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Preface

Indian Power system is growing rapidly. It plays an important role in economic growth of

the country. Power system network is witnessing phenomenal changes and new power

system elements are added to the network at quick intervals. Under these conditions

operating and maintaining the grid in a satisfactory manner is a challenge.

In order to deal with contingencies like partial or total black out in the Northern Region,

NRLDC is regularly updating the document called System Restoration Procedure for

Northern Region in line with provision in section 5.8 of the Indian Electricity Grid Code

(IEGC). The revised version of system restoration procedure is in front of you. This

procedure is revised in consultation with the constituent members of Northern Region

grid.

Chapter-1 of this procedure deals with the Restoration Strategies and General Guidelines

during restoration. As no two grid disturbances are similar, the contents of this chapter

are very useful for handling any contingency.

Chapter-2 of this procedure gives overview of northern region system restoration

procedure. Based on geographical boundaries and for ease and speedy restoration,

northern region power system is divided into four sub-systems namely Eastern UP, North-

Central, Rajasthan and Western UP/ Uttarakhand sub-system.

Chapter-3 to Chapter-6 of this procedure gives detail description of restoration

procedure in each sub-system. For easy reference these four chapters has been divided

into following sub-sections: Sub-system overview, Sub-System Restoration Procedure,

Sub-System synchronization and Restoration stages and start-up sequence in a sub-system.

Chapter-7 of this procedure gives detail description of handling Railway traction supply in

the northern region.

Chapter-8 and Chapter-9 of this procedure gives guidelines to be followed at HVDC back

to back stations at Vindhyachal and Sasaram. Chapter-10 describes the Mock blackstart

procedures of Hydro stations in Northern region. Chapter-11 gives the summary of actual

restoration during Grid disturbance on 2ndJanuary 2010, 30th& 31stJuly 2012

In addition to these nine chapters, seven annexure have been added at the end of this

procedure for quick accessibility of power maps, generator locations, reactive power

management tools, and Fault level and line parameters.

We are sure that this revised version of System restoration Procedure for Northern

Region would be helpful in dealing with any contingency in the region. All efforts have

been made to make this book error free and up to date. However, in view of the fast

changing network conditions, it is possible that some of the changes could have not been

incorporated as per actual. Any feedback from the users of the book is most welcome as it

will help us to improve the overall quality, style and presentation of the book in future.


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Table of Contents NRLDC

System Restoration Procedure for Northern Region-2013 i

System Restoration Procedure for Northern Region

Table of Contents

Chapter-1: Restoration Strategies and Guidelines..................................... 11.1. Blackouts...................................................................................................................... 11.2. Restoration Strategies................................................................................................. 11.3. General Guidelines...................................................................................................... 31.4. Priorities during system restoration......................................................................... 41.5. Line Charging Guidelines during Restoration........................................................... 41.6. Guidelines for over voltage control during Restoration.......................................... 61.7. Emergency operating instructions for operation of Power Stations under

emergency situations including islanded operation................................................ 81.8. General precautions to be followed during synchronization of a sub-system with

another sub-system:.................................................................................................... 91.9. General guidelines for blackstart by hydro/ gas staions:...................................... 101.10. CEA guideline for blackstart and synchronous condenser mode of operation of

Hydro generators:...................................................................................................... 10IEGC Guidelines for operation of grid following a blackout.................................. 11

1.11. 111.12. IEGC Guidelines for long-term access, Medium term and short-term open access

during a grid disturbance.......................................................................................... 111.13. IEGC guideline for development of recovery procedures for restoration of grid 111.14. IEGC guideline for reportable events....................................................................... 111.15. IEGC guidelines for event reporting........................................................................ 121.16. Crisis & Disaster Management in Electricity grid & Transmission lines:............ 12

Chapter-2: Overview of NR System Restoration Procedure.................... 172.1. Introduction to Northern Region Electricity Grid.................................................... 172.2. Northern Region System Restoration...................................................................... 172.3. Restoration of Power Supply to Nuclear Stations.................................................. 182.4. Restoration of power supply to Railway Traction................................................. 192.5. Start-Up Power from Western Region...................................................................... 192.6. Start-Up Power from Eastern Region....................................................................... 192.7. Load Generation Balance and Spinning Reserve................................................... 20 2.8. Black Start of Gas Stations....................................................................................... 212.9. Voltage Control during build-up of system............................................................. 212.10. Monitoring of air pressure at substations............................................................... 222.11. SCADA system during blackout............................................................................... 222.12. Mock trials................................................................................................................... 22 2.13. ISLANDING SCHEME................................................................................................. 232.14. Synchronous Operation of N-E-WGrid................................................................. 24 Exhibit -2A: Northern Regional Grid: Major Subsystems ....................................................... 25Exhibit -2B:Northern Regional Grid: Subsystems Synchronization ...................................... 27

Chapter-3: Restoration of Eastern U.P. Subsystem.................................. 293.1. Subsystem Overview................................................................................................. 29

3.1.1. Important Connecting Links with other Subsystems:.............................. 29

3.1.2. Major Generating Stations:.......................................................................... 303.1.3. Sources of Start - up Power:........................................................................ 303.1.4. Requirement of Start-up Power:................................................................. 303.1.5. System Synchronization:............................................................................ 30

3.2. Subsystem Restoration Procedure.......................................................................... 313.2.1. Vindhyachal HVDC (Back to Back Station)................................................ 323.2.2. Singrauli (STPS)............................................................................................ 323.2.3 Rihand (Hy) or (Pipri).......................................................................................... 343.2.4 Renusagar............................................................................................................ 343.2.5 Rihand (STPS)............................................................................................... 363.2.6 Anpara........................................................................................................... 36


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3.2.7 400 kV Allahabad (PG).................................................................................. 373.2.8 400 kV Kanpur (PG)....................................................................................... 373.2.9 Obra (Hy)........................................................................................................ 383.2.10 Obra (Th): 400 kV side................................................................................. 383.2.11 400 kV Panki....................................................................................................... 383.2.12 Unchahar....................................................................................................... 383.2.13 Sasaram HVDC (Back to Back Station) ...................................................... 39

3.2.14 400 kV Sarnath............................................................................................. 393.2.15 220 kV Sahupuri........................................................................................... 393.2.16 Obra (Th): 220 kV side................................................................................. 403.2.17 400 kV Azamgarh......................................................................................... 403.2.18 220 kV Allahabad (UP)................................................................................. 403.2.19 220 kV Fatehpur................................................................................................ 413.2.20 400 kV Sultanpur.............................................................................................. 413.2.21 220 kV Tanda TPS......................................................................................... 413.2.22 400 kV Gorakhpur (PG)..................................................................................... 423.2.23 400 kV Balia (PG)............................................................................................... 423.2.24 Rosa.............................................................................................................. 42

3.3. Synchronization......................................................................................................... 453.3.1. Synchronization with North-Central (NC) Sub-System.......................................... 453.3.2. Opening of the Vindhyachal Back to Back AC bypass link................................... 45

3.4. Start Up Stages And Sequence............................................................................... 47Exhibit-3A: Eastern U.P. Subsystem: Restoration Stages..................................................... 49Exhibit-3B:Eastern U.P. Subsystem: Start-Up Sequence..................................................... 51Exhibit-3C:132 kV Network around Renusagar .................................................................... 53

Chapter-4: Restoration of North-Central (NC) Subsystem....................... 554.1. Subsystem Overview................................................................................................. 55

4.1.1. Important Connecting Links with other Subsystems:.............................. 554.1.2. Major Generating Stations:.......................................................................... 554.1.3. Sources of Start-up Power:.......................................................................... 564.1.4. Requirement of Start-up Power and other Essential Loads: ................... 574.1.5. System Synchronization:............................................................................. 57

4.2. Subsystem Restoration Procedure.......................................................................... 584.2.1. The North-Central (NC) sub system:........................................................... 58 4.2.2. Delhi area....................................................................................................... 58

4.2.2.1. Faridabad (Gas)............................................................................................. 594.2.2.2. Badarpur (Th) Power Station (BTPS).......................................................... 594.2.3. BBMB and Neighboring Area:..................................................................... 604.2.3.1. Panipat 220 kV (BBMB)................................................................................. 604.2.3.2. Panipat (Th)................................................................................................... 614.2.3.3. DCRTPP (Yamuna Nagar Th)....................................................................... 614.2.3.4. Indira Gandhi TPS (Jhajjar).......................................................................... 614.2.3.5. Mahatma Gandhi MGTPS (CLP Jhajjar)...................................................... 614.2.3.6. Rajiv Gandhi TPS (Kheddar)........................................................................ 614.2.3.7. Ropar (Th)...................................................................................................... 624.2.3.8. Bhatinda / Lehra Mohabat............................................................................ 624.2.3.9. Pong............................................................................................................... 634.2.3.10. Bairasiul......................................................................................................... 634.2.3.11. ADHPP............................................................................................................ 63

4.2.3.12. Baspa.............................................................................................................. 63 4.2.3.13. Karcham Wangtoo........................................................................................ 634.2.3.14. Jhakri.............................................................................................................. 644.2.4. Dadri (NTPC) area......................................................................................... 644.2.5. Auraiya (Gas) area:....................................................................................... 654.2.5.1 Auraiya Gas........................................................................................................ 654.2.5.2 400 kV Agra (PG)................................................................................................ 654.2.6. J&K and North Punjab Area............................................................................... 664.2.6.1 Ranjit Sagar HEP.............................................................................................. 664.2.6.2 Salal HEP........................................................................................................... 664.2.6.3 Chamera HEP...................................................................................................... 66


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4.2.6.3 Budhil HEP.......................................................................................................... 674.2.6.4 Uri674.2.6.5 Lower Jhelum................................................................................................... 674.2.6.6 Baglihar............................................................................................................... 674.2.6.7 Dulhasti............................................................................................................... 684.2.6.7 Sewa-2................................................................................................................. 684.2.6.8 400 kV Kishenpur............................................................................................... 68

4.2.6.9 Bhiwadi HVDC............................................................................................... 684.2.6.10 RGTPP (Khedar)............................................................................................ 684.3. Synchronization......................................................................................................... 694.4. Start-Up Stages and Sequence:................................................................................ 69Exhibit- 4A:North Central Subsystem: Restoration Stages .................................................. 71Exhibit- 4B1/2: North Central Subsystem (Part-1): Start-Up Sequence........................... 73Exhibit- 4B2/2: North Central Subsystem (Part-II): Start-Up Sequence........................... 75

Chapter-5: Restoration of Rajasthan Subsystem...................................... 775.1. Subsystem Overview:................................................................................................ 77

5.1.1. Important Connecting Links with other Subsystems:.............................. 775.1.2. Major Generating Stations:.......................................................................... 775.1.3. Sources of Start-up power........................................................................... 775.1.4. Requirement of Start-up power:.................................................................. 785.1.5. System Synchronization:............................................................................ 78

5.2. Subsystem Restoration Procedure......................................................................... 785.2.1. R.P.Sagar HEP.............................................................................................. 785.2.2. Jawahar Sagar HEP...................................................................................... 785.2.3. Kota (Sakatpura) 220 kV Sub-Station......................................................... 795.2.4. Kota (STPS).................................................................................................. 795.2.5. Giral Lignite................................................................................................... 795.2.6. RAPS (A) , RAPS (B) and RAPS (C) ............................................................ 805.2.7. Anta (Gas)..................................................................................................... 805.2.8 Dholpur CCPP...................................................................................................... 815.2.9 Ramgarh GTPP.................................................................................................... 815.2.10 Suratgarh STPS................................................................................................... 815.2.11 Barsingsar (IPP)............................................................................................ 815.2.12 Chabra TPS.................................................................................................... 825.2.13. V S Lignite (IPP)............................................................................................ 82

5.2.14. Rajwest LTPS................................................................................................ 825.2.15 Jaipur (Heerapura) 220 kV Sub-Station..................................................... 825.2.16. Khetri 220 kV Sub-Station........................................................................... 82

5.3. Synchronization........................................................................................................ 835.4. Start-Up Stages And Sequence............................................................................... 83Exhibit-5A: Rajasthan Subsystem: Restoration Stages ......................................................... 85Exhibit-5B: Rajasthan Subsystem: Start-Up Sequence.................................................... 87

Chapter-6: Restoration of Western U.P. /Uttarakhand Subsystem...... 896.1. Subsystem Overview................................................................................................. 89

6.1.1. Important Connecting Links with other Subsystems:.............................. 896.1.2. Major Generating Stations.......................................................................... 896.1.3. Sources of Start-up power.......................................................................... 906.1.4. Requirement of Start -up power:................................................................ 906.1.5. System Synchronization:............................................................................ 90

6.2. Subsystem Restoration Procedure......................................................................... 906.2.1. Yamuna Complex.......................................................................................... 916.2.2. Khara Hydro Station:........................................................................................... 926.2.3. Chilla And Maneri Bhali Hydro Stations.................................................... 926.2.4. Ramganga, Tanakpur and Khatima Hydro Stations.................................. 926.2.5. Vishnu Prayag Hydro Stations..................................................................... 936.2.6. Tehri Hydro Station....................................................................................... 936.2.7. Koteshwar Hydro Station............................................................................. 936.2.8. Dhauli Ganga Hydro Stations...................................................................... 946.2.9. Narora Island........................................................................................................ 94

6.3. Synchronization......................................................................................................... 96


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6.4. Startup Stages and Sequence:................................................................................. 96Exhibit-6A: Western U.P./Uttarakhand Subsystem: Restoration Stages......................... 97Exhibit-6B: Western U.P./Uttarakhand Subsystem: Start-Up Sequence......................... 99

Chapter-7: Power Supply to Railway Traction......................................... 101Power Supply to Railway Traction..................................................................................... 1017.2. Northern Railway (NR)............................................................................................. 1017.3. North Central Railway (NCR)................................................................................... 103

7.4. West Central Railway (WCR)................................................................................... 1047.5. North Eastern Railway (NER).................................................................................. 1057.6. Delhi Metro................................................................................................................ 1057.7. Traction Sub-Stations Schematic Diagrams......................................................... 106Exhibit-7A: Power Supply to Northern Railway Traction ...................................................... 107Exhibit-7B: Power Supply to Central & Western Railways Traction.............................. 109Exhibit-7C: List of Grid Sub-Station Feeding Railway Traction..................................... 111Exhibit-7D: Power Supply to Delhi Metro.......................................................................... 113

Chapter-8: Operation of 400 kV Vindhyachal A.C. By-Pass Link........... 1158.1. Closing Of Vindhyachal A.C. By-Pass Link........................................................... 115

8.1.1. Singrauli....................................................................................................... 1158.1.2. Vindhyachal HVDC (Back To Back)........................................................... 115

8.2. Opening Of Vindhyachal A.C. By-Pass Link........................................................ 1168.2.1. Vindhyachal HVDC (Back-to-Back)........................................................... 116

Exhibit-8: 400 KV Vindhyachal A.C. By -Pass Link.......................................................... 119Chapter-9: Operation of 400 kV Sasaram A.C. By-Pass Link................. 1219.1. Closing Of Sasaram A.C. By-Pass Link................................................................. 121

9.1.1. Sarnath......................................................................................................... 1219.1.2. Sasaram HVDC (Back to Back).................................................................. 121

9.2. Opening Of Sasaram A.C. By-Pass Link............................................................... 1229.2.1. Sasaram HVDC (Back-to-Back)......................................................................... 122

Exhibit-9: 400 KV Sasaram A.C. By -Pass Link................................................................ 123

Chapter-10: Mock Black Start Exercise................................................... 12510.1 Chamera-1 HEP mock black Start exercise........................................................... 12510.2 Uri HEP mock black Start Exercise........................................................................ 13110.3 Karcham Wangtoo Hydro mock black start exercise........................................... 13710.4 AD Hydro mock black Start Exercise..................................................................... 14310.5 Koteshwar Hydro mock black start exercise........................................................ 14910.6 Dhauliganga Hydro mock black start exercise.................................................... 15310.7 Tehri Hydro mock black start exercise................................................................. 15910.8 Jhakri Hydro mock black start exercise................................................................ 16510.9 Salal Hydro mock black start exercise.................................................................. 173

Chapter-11: Actual restoration during Grid disturbance on 2ndJan 2010,30th& 31stJuly 2012................................................................................... 17911.1 Summary of actual restoration during grid disturnabce on 2

ndJanuary 2012.. 179

11.1.1 Restoration after event at 0301 hrs:.......................................................... 17911.1.2 Restoration after event at 2154 hrs:.......................................................... 183

11.2 Restoration Sequence after Grid Disturbance on 30th July 2012....................... 18911.2.1 Restoration Process in Northern Region................................................. 18911.2.2 Revival of Interconnection with Eastern Region..................................... 198

11.3 Restoration Sequence after Grid Disturbance on 31st July 2012....................... 199

11.3.1 Extension of Power Supply........................................................................ 19911.3.2 Extension of startup supply to Power Stations....................................... 19911.3.3 Black start by Hydro stations, formation of sub-system & theirsynchronization............................................................................................................ 20211.3.4 Restoration of Traction Supply................................................................. 20511.3.5 Pictorial Representation of Restoration in Northern Region................. 208

Annexure.................................................................................................... 211Annexure-I.................................................................................................. 213400 kV Geographical Map of Northern Region................................................................. 213

Annexure-II Reactive action plan.............................................................. 215


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System Restoration Procedure for Northern Region-2013 v

Annexure-III................................................................................................ 217Network Diagram and Power-Maps................................................................................... 217Power Map Punjab............................................................................................................... 219Power Map Haryana............................................................................................................ 221Power Map Rajasthan......................................................................................................... 223Power Map Delhi.................................................................................................................. 225Power Map Uttar Pradesh................................................................................................... 227

Power Map Uttarakhand...................................................................................................... 229Power Map Himachal Pradesh........................................................................................... 231Power Map Jammu & Kashmir........................................................................................... 233Power Map Chandigarh....................................................................................................... 235Power Map Northern Region-400 kV Network Diagram................................................... 237Northern Region Geographical Diagram Indicating Generators Location.................... 239

Annexure-IV................................................................................................ 241Ready Reckoner on Reactive Power Management.......................................................... 241

Annexure-V................................................................................................. 243List of Line Reactors in Northern Region......................................................................... 243

Annexure-VI................................................................................................ 247List of Bus Reactors in Northern Region.......................................................................... 247

Annexure-VII............................................................................................... 251

Summary of Fault Level at 400 kV Buses in Northern Region........................................ 251Annexure-VIII.............................................................................................. 253Line Parameters and Surge Impedance Loading of Different Conductor Type ............ 253

Annexure-IX................................................................................................ 255Islanding Schemes in Northern Region............................................................................ 255

I. NAPS islanding scheme............................................................................. 255II. RAPS-A islanding scheme......................................................................... 257III. RAPS-B islanding scheme......................................................................... 261IV. Delhi Islanding scheme (proposed).......................................................... 265V. Scheme for revival and operation of Kashmir valley in island after itscollapse (proposed)..................................................................................................... 275

Annexure-X................................................................................................. 277Format for Quarterly Report on Mock drill for crisis management plan in Power sector ....... 277

Annexure-XI................................................................................................ 279I. Nodal officers for concerned RLDC/SLDCs for Disaster Managementin Power Sector .............................................................................................................. 279II. Contact details of load dispatch centres for disaster management in powersector 281

Annexure-XII............................................................................................... 283Details of Black start capability of Hydro and Gas Power Stations ....................................... 283

Bibliography............................................................................................... 287


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System Restoration Procedure for Northern Region-2013 vii

Generating Station Index

A

Anpara, 36Anta (Gas), 80Auraiya (Gas), 65

B

Badarpur (Th), 59Baglihar, 67Bairasiul, 63Baspa, 63BBMB, 60Bhakra, 60Bhatinda, 62

C

Chamera HEP, 66, 67Chibro, 91

Chilla, 92

D

Dadri (NTPC), 64Dhakrani, 91Dhalipur, 91Dhauli Ganga, 94Dholpur, 81Dulhasti, 68

F

Faridabad (Gas), 59

GGiral, 79

J

Jaipur 220 kV, 82

Jawahar Sagar HEP, 78Jhakri, 64

K

Khara Hydro, 92Khatima, 92Khetri, 82

Khodri, 91

Kota (STPS), 79Kulhal, 91

L

Lehra Mohabat, 62

M

Maneri Bhali, 92

N

Narora, 94

O

Obra (Hy), 38Obra (Th), 38, 40

P

Panipat (Th), 61Panki, 38

Pong, 63

R

R.P.Sagar HEP, 78Ramganga, 92Ramgarh, 81Ranjit Sagar HEP, 66RAPS (A), 80RAPS (B), 80Renusagar, 34Rihand (Hy) (Pipri), 34Rihand (STPS), 36Ropar (Th), 62

S

Salal HEP, 66Singrauli (STPS), 32Suratgarh STPS, 81, 82

T

Tanakpur, 92Tanda, 41Tehri Hydro, 93

U

Unchahar, 38

V

Vindhyachal HVDC, 32Vishnu Prayag, 93


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Chapter-1: Restoration Strategies and Guidelines. NRLDC

System Restoration Procedure for Northern Region-2013 1

Chapter-1: Restoration Strategies and Guidelines

1.1. Blackouts

A total power failure over a large area usually caused by the failure ofmajor generating equipment or transmission facilities. The possiblecauses of blackouts identified from literature survey and from review ofpast incidents are as listed below:

Fault at a focal point in the grid Delay in fault clearance Tripping of large generating units Cascade tripping of transmission line(s) resulting from tripping

of a heavily loaded transmission line Cascade tripping of ICTs due to overloading Equipment failure

Protection mal-operation Slow response of generating units Slow response of manual load shedding during low frequency Inclement weather (heavy rainfall, fog, dust storm etc.) Inadequate reactive reserves leading to voltage collapse Inadequate safety net in the form of under frequency, Under

Voltage, Rate of Change relay load shedding, Human error Combination of above events

1.2. Restoration Strategies

Grid disturbance can occur in the grid due to several reasons. Each one is unique in itscharacteristics and impact. It would be difficult to prescribe a single solution that fits all

scenarios. However the general philosophy and guidelines for system restoration elaborated in

this document may be useful in reducing the restoration time in effective manner. Therestoration activities following a blackout have been divided intofollowing broad categories.

Bottom-Up Approach -Systems with a fair dispersal of generating unitsWith black start facilities:

a) Formation of sub-systems :-Those generating stations, where black startfacilities are available

(i.e., hydro units, gas turbines etc.) should be started up and sub-systems be formed around them by connecting essential loads.Those generating stations will provide start-up power to remaininggenerating facilities within the sub-system. The subsystem shouldhavesufficient generation to supply most of the load within the sub-system and primary response from the generating units becomeimportant to avoid any secondary collapse due to frequencyfluctuations.


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System Restoration Procedure for Northern Region-20132

b) Restoration of individual sub-systems :-i. Immediately after a blackout, the operators in the blackout area

shall openall circuit breakers and restart the black start unit inthe respective subsystem. The operators would then makeefforts to establish a path between the self-started units andother thermal/ hydro units, whichrequire offsite start-up power.

Along the path, some critical loads would be restored forstabilizing the black start units. Supply to other customerswithinthe sub-system can be provided after adequate generation isavailable within the subsystem.

ii. Utmost care should be taken, while adding loads, to ensurestep-bystep addition, keeping strict vigil of the loadcharacteristics, i.e. variation of load with respect to voltage andfrequency and stiffness of the subsystem. The general guide isto pick up load when the system frequency is high and increasegeneration when system frequency is low. Restore smaller andradial loads prior to larger and low voltage AC network load,while maintaining a reasonably constant real to reactive powerratio. Essential loads can be restored in steps less than 5 MW.

iii. During cold load pickup, sudden starting of motor of power plantauxiliaries like Boiler Feed Pump (BFP), Induced Draft (ID) fans& Forced Draft (FD) fans, pulverizing mills, long conveyors etc.,can cause voltage dips due to drawing of high starting currents.

iv. While starting the power station auxiliaries, it is preferable tostart the largest motor first, if the start up sequence permits.When the next largest motor is started, the running motor acts

as an induction generator and helps in controlling the startingcurrent. Further, larger motors along with their rotating loadsmay act as flywheel and prevent jerks to the generators. It isalso preferable to connect some radial loads to black startedunits before extending start-up power to other stations. It is alsopreferable to restore rotating type loads, which contributes toinertia of the island. In all cases, load pick up should berestricted so as to avoid frequency excursions by more than 0.5Hz in the island.

c) Synchronization of the sub-system:After each sub-system is reenergized,the last step in the

restoration procedure is to resynchronize these subsystems.These subsytems are interconnected at predefined locationswhere synchronizing facilities are available. The speed ofrestoration enhances with increase in number of black startfacilities and their dispersal. It isrequired to carefully monitor theoperations of the islands (before reintegration with rest of thegrid) due to small stiffness in islands.


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Top-Down Approach - Systems with no / less generating units withblackstart facilities:

a) The second approach could be followed in case self start facilities areavailable at only a few power stations or the start up power has to beimported from neighbouring areas/regions at one or two points. In this

case, the start up power is required to be extended to all thegeneratingstations on priority basis while restoring few loads andtransformers/reactors for voltage control.

b) The start-up power available from neighbouring regions at variousinterconnection have to be seriously explored since considerableassistance can be availed and the restored system is likely to beconnected to a stable external system. These procedures are to bewell planned for the earliest and quickest harnessing of the facilities.The restoration through this approach could be delayed due toproblems incharging the lines viz. high-voltage, etc.

1.3. General Guidelines

1. A subsystem should

Contain at least one unit with black start capability. Be able to supply startup power to non-self starting units within

subsystem. Be able to supply essential loads within subsystem.

2. Strict active power balance is to be maintained while building up thesubsystem. Voltages in the subsystem are to be closely monitored

and all available reactive resources are to be judiciously used formaintaining the voltages within permissible range.

3. Simultaneous, immediate and independent measures should betaken to supply station service for the hot start of the boilers beforeelapse of the allowable time interval between shutdown and hotrestart. This interval is usually of the order of half an hour or less.

4. Interconnection of generating stations within each sub-systemshould be done as soon as possible. Such an interconnectionshould be carried out after generating units attain the minimumspecified generation, but prior to restoration of full load within the

sub-system.

5. Switching in and switching out of load in the subsystem should bedone in small quantum to avoid excessive frequency deviation. Thegeneral guide is to pick up load when the system frequency is highand increase generation when system frequency is low. Restoresmaller and radial loads prior to larger and low voltage AC networkload, while maintaining a reasonably constant real to reactive powerratio.


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6. Maintaining steady state stability by having loads in vicinity of each

station supply is important.

7. Maintain system voltage within plus and minus 5% by maintaininggenerator voltages at low end of range during early stages of

restoration and adjusting transformer taps to appropriate positions.In case of hydro stations it is desirable to operate more number ofunits at 0-10 % loading so that dynamic reactive reserves areavailable.

8. Energizing only one circuit of the double circuit transmission lines,and operating generators under excited (i.e. in the leading mode) tothe extent that stability considerations allow is recommended duringthe early stages of restoration from voltage considerations.However redundancies in the network should be built up as soon aspossible by way of restoring parallel circuits between two points.

9. While energizing a system from 220 kV voltage side, bring thetransformer tap position to its nominal or towards lower turns ratio.(i.e. between 9 & 17 in a typical 1 to 17 tap transformer.)

1.4. Priorities during system restoration

1. Extending power for synchronizing islanded nuclear power stationsor startup power to nuclear power plants.

2. Extending start-up power to thermal power plants.3. Extending start-up power to non-self starting hydro power plants.4. Restoration of traction power supply.

5. Building up subsystem and synchronizing with each other.6. Restoration of supply to other essential loads such as Hospitals etc.7. Restoration of supply to all other customers.8. Power stations which receive startup power may extend supply to other

near by power stations for start up without waiting for code from NRLDC.9. Code may be taken from NRLDC for synchronization if start up supply is

available from two different sources.

This document covers Sl. no. 1 to 5 above. It is expected that atstate level, each SLDC /distribution company would have a similarprocedure for restoration of essential consumer load with in thestate.

At the same time due priority shall also be given to restore powersupply to communication system nodes and repeater stations.

1.5. Line Charging Guidelines during Restoration1. Ensure that line to be charged is free from fault. i.e. faulted line

shall not be charged (or used in the restoration procedure).

2. Before charging, ensure that communication is available betweenboth ends and protections are in service and no protection is by-


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passed.

3. During restoration, lines of lower voltage levels should be given firstpriority.

4. The line should be charged from the end with higher fault level in

order to limit the over voltage at charging end.5. In case one bus is completely dead, charge the line from the other

end, which is live and close the breaker at the dead bus end.Before closing all other breakers should be opened at the dead busend.

However, the bus/line reactors may be kept in service (as perrequirement) with breaker/isolator in closed position before chargingthe dead bus.

6. If two buses have almost same short circuit level (3-ph) and neitheris a generation station, charge the line from the bus with lowervoltage. At the charging end, all measures should be taken tocontrol high voltage

a. Bus reactors may be taken in to serviceb. Generators at the charging end may be operated at reduced

voltage (less than 1 pu.) and in leading power factor modec. Suitable measures may be taken to avoid large frequency

variationsd. Loads may be taken into service in small steps

7. At the synchronizing end, control of standing phase angle (SPA) to

less than or equal to 20

o

would help in minimizing jerk or suddenrush of power. For reduction of SPA, the following measures needto be taken up.

a. Reduce generation at those generators that are sensitive to theSPA.

b. Shed loads at selected buses.c. Simultaneous backing down of generation and shedding of load.d. Increase of generation at the sensitive buses.

The recommended practice for synchronizing lines is alwaysthrough check synchronization relay that normally is set for 35

(above which breaker closing is not permitted). For most of thelines, SPA < 35 would suffice. However, in case of lines interconnecting two major generating stations; it is prudent to limit the

SPA to around 20.

8. Open-end voltage should not exceed the voltage level at whichover-voltage protection operates (generally 110%) of nominalvoltage. Reducing the voltage at the charging end could control theopen-end voltage. The end with lower voltage would be ideal for


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charging as this minimizes the rise of voltage at the open end.

9. If the open-end voltage is too high, line charging VARs wouldincrease and it may be difficult for the charging end to sustain thevoltage increase. Ensure adequate voltage control measures at thecharging end to contain high open-end voltage. Keep the charging

end voltage as low as possible. If required transformers at thecharging end may be used as bus reactors by keeping it energizedwhile line charging.

10. While back charging long 400kV lines, the problem of Ferro-resonance may occur. Hence, adequate measures such as takingbus/tertiary reactors in to service and most importantly some loadon the transformer shall be taken.

11. When one end is generating station end.While charging a line from generating stations during restoration,care should be taken to ensure that sufficient generation isavailable and/or connections with other stations at the charging endto absorb the (leading VARs) reactive power without difficulty.Before charging, ensure by addition of load preferably or throughexcitation control, that these generators are operating in such amanner that sufficient margin are available for absorbing linecharging MVAR. Also ensure that, the generator EHV bus voltagesare kept low around 0.9 per unit or even less by excitation control toensure less open-end voltage rise.

In case of hydro stations, it is suggested that 2-3 units may be keptrunning to have larger dynamic reactive reserves to facilitate (220-

400 kV) line charging.

12. One end Line Reactor Available

In case, line reactor is available at only one end, it is preferable tocharge the line from the end without reactor and synchronize at theend with reactor.

If the line is to be opened, open from the end where line reactor isavailable.

Thumb rule is synchronize or open from the end where line

reactor is available.

1.6. Guidelines for over voltage control during Restoration

1. Taking into account the equipment voltage limitations and faultcontingency, it is recommended that no line shall be energized if bydoing so, the voltage at the remote end would rise to more than 1.2pu. Of normal or 1.1 x (transformer tap or circuit breaker ratedmaximum voltage), whichever is lower?


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2. Sustained over voltages can be controlled by absorbing the large

charging reactive power of the lightly loaded transmission lines.This can be accomplished by:

1 Having sufficient under excitation capability on the generators,

2 Connecting reactive loads (lagging power factors) to theunderlying system including shunt reactors,

3 Removing all sources of reactive power and switching off shuntcapacitors,

4 Operating parallel transformers on different taps to increasecirculating currents and reactive power losses,

5 Energizing only those transmission lines which carry significantload and avoiding the energization of extra lines which willgenerate unwanted reactive power, and

6 Maintain a low voltage profile on the transmission line, since thecharging currents are proportional to the square of the voltage.

3. The extent of the generation voltage reduction is usuallyconstrained by under excitation of generators by a number oflimiting factors, including generator terminal low voltage limit (aslimited by power plant auxiliary equipment), reactive ampere limitrelay, minimum excitation limit relay, and rotor core and heatinglimit.

4. Switching transients are not usually the limiting factors inreenergizing a system. Generally, if the steady state voltages areless than 1.2 per unit of their nominal values, the switchingtransients can be managed by typical arrestors with ease. Based onthe experience of mock blackstart exercises of charging long linesfrom generating stations, it is recommended that whenevercharging a long line in the weekly connected system, a delay of 100ms shall be introduced (only during charging) in the Overvoltagestage-II (at 150 % over-voltage) protection which is otherwiseinstantaneous. A notable exception is energizing transformer-terminated lines, which may result in harmonic resonance and

damaging over voltages.

5. Control of Harmonic resonance:

a) Sustained harmonic over voltages caused by over excitation oftransformers, can be controlled by selecting a transformer tapwhich equals or exceeds the power frequency voltage applied(or lowering system voltage to at or below the tap) beforeenergizing.


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b) Harmonic resonance can be damped by connecting sufficientunderlying loads at the sending end of a line, or by connectingdead load on the transformer to be energized.

c) High source impedance can be reduced by starting moregenerators and connecting underlying loads.

d) The reactive power of a lightly loaded system can be reduced byminimizing the number of unloaded lines to be energized andsetting the sending-end transformers at the lowest tap position.

1.7. Emergency operating instructions for operation of Power Stationsunder emergency situations including islanded operationThese instructions are for situations when an island has been formedrandomly and not by design. (Say, part of under frequency islandingscheme.)

1. In case of any disturbance in the system, SLDC/NRLDC wouldidentify whether any power station has survived or not.

2. In case power plant has survived SLDC/NRLDC would identifythe island formed, if any, and determine its size (in MW). All thepower stations and substations forming part of this island wouldbe informed accordingly.

3. RLDCs/ SLDCs would advise the substations forming part of theisland not to connect/disconnect any load (including anyscheduled rostering) unless instructed by the SLDC or PowerStation. These substations would be on a high alert.

4. In case any power plant output within the island is expected todecrease due to problem with any auxiliary, it would immediatelysend an SOS to the adjacent substation for shedding thequantum of load. All telephone numbers required for the purposeshould be available with the power station operating personnel.

5. In case the substation load is expected to go up normally as perits load profile, load shedding in small steps would be done inadvance so that the frequency is maintained close to 50.5 Hz.

6. In case of frequency remaining above 51 Hz, the power station(s)in the island would control the same and maintain it around

50.5Hz.

7. Simultaneously SLDC would identify the point of synchronization inco-ordination with NRLDC and take steps to synchronize thesubsystem with the main grid. In case the power stations in theisland has many feeders out of which some has tripped, it might bepreferable to extend the grid supply to the power station on thesefeeders so as to facilitate quick synchronization of supply at thepower station itself.


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1.8. General precautions to be followed during synchronization of asub-system with another sub-system:

a) A strict load-generation balance shall have to be maintained whiledeveloping the subsystem.

b) Due to start up of the areas separately, the related supplies are tobe synchronized at the earliest opportunity and a combinedsubsystem is to be formed at the earliest for strengthening thesubsystem.

c) The railway traction load at the various points and start up suppliesto generating stations is to be extended on top priority.

d) The voltages at different nodes / buses are to be maintained withinnormal range by the use of bus / line reactors and by operating theunits in synchronous condenser mode wherever applicable forabsorbing /generating VARs. The synchronous condenser

operation has a stabilizing effect on the system voltage and theadditional mechanical inertia helps when system load variesquickly.

e) In respect of large hydro power stations connected on 400 kVsystem, after self-starting of the hydro units and before charging a400 kV line from the power station end, the bus reactor(s) at theremote end should be taken in service and keep the breaker of theline closed at the remote end. This will ensure that as soon as theline is charged from the power station end both the line reactor (ifany) and bus reactor will come into service at the remote end.

f) The recommended practice for synchronizing lines is alwaysthroughcheck synchronization relay that normally is set for 35(above which breaker closing is not permitted). For most of thelines, SPA < 35 would suffice. However, in case of lines interconnecting two major generating stations; it is prudent to limit theSPA to around 20. Typical specifications of check synchronisingrelay indicated in below given table.

Typical Check Synchroniser Type and Settings-Make: AlstomType: SKD and SKE Check synchronising relays


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50

()

D A

350

+0% 5%

35 2 0.19

. 80

90%

35 3 0.13

35 4 0.09

35 5 0.08

35 6 0.06

35 10 0.04

E

200

+0% 5%

20 0.5 0.45

D

.

2%, 4%,

6%, 8%, 10%

20 1 0.22

20 1.5 0.15

20 2 0.11

20 2.5 0.09

20 3 0.07

100

+0% 5%

10 0.25 0.45

10 0.5 0.22

10 0.75 0.15

10 1 0.11

10 1.25 0.09

10 1.5 0.07

1.9. General guidelines for blackstart by hydro/ gas staions:Incase of blackout, the generating stations equipped with black-startfacility shall initiate actions to self-start and create a subsystem in-

coordinationwith the adjacent substation without waiting for explicitoperation code from NRLDC. However operation code from NRLDCmust essentially be taken prior to synchronization of subsystems

1.10. CEA guideline for blackstart and synchronous condenser modeof operation of Hydro generators:As per CEA technical standards for grid connectivity to grid,regulations 2007, part-II, applicable to the generating units,a. Clause 10

Hydro generating units having rated capacity of 50 MW and aboveshall be capable of operation in synchronous condenser mode,wherever feasible.

b. Clause 14In case of hydro generating units, self-starting facility may beprovided. The hydro generating station may also have a smalldiesel generator for meeting the station auxiliary requirements forblack start.


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1.11. IEGC Guidelines for operation of grid following a blackout

According to IEGC Para 5.8(d) The RLDC is authorized during therestoration Process following a blackout, to operate with reducedsecurity standards for voltage and frequency as necessary in order toachieve the fastest possible recovery of the grid.

1.12. IEGC Guidelines for long-term access, Medium term and short-term open access during a grid disturbanceAs per point no.17 of clause 6.5 for Scheduling and Despatchprocedure for long-term access, Medium term and short-term openaccess:In case of any grid disturbance, scheduled generation of all the ISGSand scheduled drawal of all the beneficiaries shall be deemed to havebeen revised to be equal to their actual generation/drawal for all thetime blocks affected by the grid disturbance. Certification of griddisturbance and its duration shall be done by the RLDC

1.13. IEGC guideline for development of recovery procedures forrestoration of gridAs per IEGC Clause 5.8a. Detailed plans and procedures for restoration of the regional grid

under partial/total blackout shall be developed by RLDC inconsultation with NLDC, all Users, STU, SLDC, CTU and RPCSecretariat and shall be reviewed / updated annually.

b. Detailed plans and procedures for restoration after partial/totalblackout of each Users/STU/CTU system within a Region will befinalized by the concerned Users/STU/CTU in coordination with theRLDC. The procedure will be reviewed, confirmed and/or revised

once every subsequent year. Mock trial runs of the procedure fordifferent subsystems shall be carried out by the Users/CTU/STU atleast once every six months under intimation to the RLDC. DieselGenerator sets for black start would be tested on weekly basis andtest report shall be sent to RLDC on quarterly basis.

1.14. IEGC guideline for reportable eventsAs per IECC Clause 5.9.5Any of the following events require reporting by RLDC/ Users, SLDC,STU, CTU:a. Violation of security standards.b. Grid indiscipline.

c. Non-compliance of RLDCs instructions.d. System islanding/system splite. Regional black out/partial system black outf. Protection failure on any element of ISTS, and on any item on the

agreed list of the intra-State systems.g. Power system instabilityh. Tripping of any element of the Regional grid.i. Sudden load rejection by any User


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1.15. IEGC guidelines for event reportingAs per IEC clause Clause 5.9.6

a. Written reporting of Events by Users, STU, CTU and SLDC toRLDC:In the case of an event which was initially reported by a User, STU,

CTU or a SLDC to RLDC orally, the User, STU,CTU ,SLDC will givea written report to RLDC in accordance with this section. RLDC inturn give a report to NLDC.

b. Written Reporting of Events by RLDC to Users, STU, CTU andSLDC. In the case of an event which was initially reported by RLDCto Users, STU, CTU SLDC, NLDC orally, the RLDC will give awritten report to the Users, STU,CTU, SLDC,NLDC in accordancewith this section.

c. Form of Written Reports:A written report shall be sent to NLDC, RLDC, ,a User,STU,CTU,SLDC, as the case may be, in the reporting formats asdevised by the appropriate load despatch Centre and will confirm theoral notification together with the following details of the event:I. Time and date of eventII. Location

III. Plant and/or Equipment directly involvedIV. Description and cause of eventV. Antecedent conditions of load and generation, including

frequency, voltage and the flows in the affected area at the timeof tripping including Weather Condition prior to the event

VI. Duration of interruption and Demand and/or Generation (in MW

and MWh) interruptedVII. All Relevant system data including copies of records of allrecording instruments including Disturbance Recorder, EventLogger, DAS etc

VIII. Sequence of trippings with time.IX. Details of Relay Flags.X. Remedial measures.

1.16. Crisis & Disaster Management in Electricity grid & Transmissionlines:

1.16.1 Crisis Management Plan for Restoration of Transmission Lines

Transmission lines are the arteries of the Electricity grid andthese are most prone to damage due to earthquake, cyclone,terrorist attack, flood, etc.Under extreme wind conditions, the conductors of transmissionlines may get snapped or transmission line towers may collapse.The floods, landslides and earthquakes cause damage to orfailure of foundations of towers, which may sometime lead todisruption of the transmission network due to uprooting of


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foundations and consequent collapse of the tower. The floodsalso cause disruption in power transmission in case substationsare affected by the floods. In addition to this, terrorist attack, fireaccident may also cause damage to transmission lines, loaddispatch centres & sub-stations which, in certain cases, may inturn lead to grid failure. Various faults, equipment failure/mal

operations are other common causes of grid failure. Possiblemishaps in transmission system in the event of disasters due tovarious natural calamities and crises are as under:

a. Snapping of conductorb. Collapse of transmission towerc. Washing away of foundation for river crossing towersd. Landslides in hilly terrains affecting towers of the linee. Flooding of sub stationsf. Destruction / Fire in sub stations

1.16.2 Crisis Management Plan for Failure of Electricity Grid

The Power systems are planned and developed to meet thereliability criteria envisaged in Indian Electricity Grid Code(IEGC) The Load Despatch Centres to enable the systemoperators to ensure safe and secure integrated operation of thepower system in the respective region/state. Despite theavailabilities of state of the art techniques, grid disturbances dotake place to various reasons and dynamics in the systembeyond the control of the operators. In most of the situationsdisturbances involve a small portion of the grid which can beeasily restored by extending power from the neighboring healthy

system.

Integrated operation of vast and complex electricity grid like theone existing in the country demands utmost vigil and care fromdisaster point of view. Attacks at key grid sub-stations, powerstations transmission lines or computer-based load dispatchcenters could black out the entire region for considerable periodof time.

In the event of a grid failure, coordinated actions are required tobe taken at the generating stations, substations andtransmission lines under the directions of RLDC(s) and SLDC(s)

for speedy restoration of power supply. Black Start / RestorationProcedures are already formulated by each RLDC for use in theevent of partial / complete failure of the grid identifying inter-aliathe start up power availability and restoration procedures.

1.16.3 Measures for Quick Restoration of Power Supply

Following measures are essentially required for quick restorationof power after a black out:


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a. The start-up procedure for the generating units should beknown to every one and working level personnel should startthe machines without referring to or waiting formanagements consent during the crisis.

b. Shift duty personnel should be detained till the restorationprocess is completed before handing over charge to next

shift.c. Survival / Auxiliary / Start-up power should be provided to the

collapsed system till requirement on priority basis and powershould be utilized for other purposes only after meeting thesepower requirements.

d. Priority should be accorded in restoration as under:e. Survival/start-up power to nuclear unitsf. Survival power to deep gassy minesg. Restoration of power supply to generating stations & Load

Despatch Centre(s)h. Start-up power to hydro and gas unitsi. Formation of self-sustaining islands around the generating

stations as per laid down procedurej. Area Load Dispatch concept should be adopted during start-

up to avoid jamming of communication system as well as forease in decision making.

k. Loading of generator supplying the start-up power should notexceed 80% of its capacity. Efforts should be made to keepthe generator operating on lagging side; if not possible, atleast to near unity power factor.

1.16.4 Facilities Required to Tackle Crisis situationsa. Recovery Equipment and Spares Inventory

b. Communication Facilities:c. Transport and Other Arrangements:d. Financial Resources:e. Black Start Facilities:f. De-watering Pumps:g. Mobile DG Sets

1.16.5 Other Essential Requisites to Handle Any Disastera. Fire alarm and extinguishing system to be checked regularly

for its healthiness and regular drill should be carried out for itsoperation by involving the officers and staff of that Unit so thatthey also know how to operate the system.

b. Safety audit must be carried out at each generating stationand sub station on yearly basis.

c. There should be perfect interaction on continuous basisbetween various crisis management groups and stateagencies against terrorist attacks.


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d. State level support groups shall identify category-wise all the

generating, sub-station grid centers and load dispatch centersbased on their strategic importance. The highest vulnerablecenters shall be provided the highest type of security.

e. The islanding schemes (electricity grid) of each state must beupdated on continuous basis in consultations with theRegional Electricity Board.

f. Each Regional Load Dispatch Center must identify all thegenerating stations/grid sub-stations and load dispatchcenters according to their critical importance with respect tosafe operation of the electricity grid. The highest criticalstation must be provided the highest security arrangementand it may go on reducing to the least risk element, withoutjeopardizing the safety of electricity grid.

g. Each Utility shall create a fund for meeting the requirement ofdisaster management plan. The disaster management fundwould be 1% of the annual revenue of the station/Utility. Thefund would be non lapsable and would be accumulated. Thedisaster management funds would be at the full discretion ofEmergency Management Group once emergency has beendeclared.

h. Carry out comprehensive state wise mock drills periodically(at least once in every six months) to test capabilities.Emergency scenarios shall be developed to test the

emergency plans and operational response at all levelsthrough mock exercises. At the end of each exercise anevaluation of the response call shall be carried out to takecare of any deficiency noticed.

1.16.6 A quarterly report of mock drills regardingthe crisis Management Plan in Respect of MOP is to beforwarded to CEA. The sample report format as received fromCEA is attached at annexure-X. Also the list of Nodal officersfor concerned RLDC/SLDCs for Disaster Managementin Power Sector along with the contact details of controlrooms is attached at annexure-XII.


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Chapter-2: Overview of NR System Restoration Procedure NRLDC


Chapter-2: Overview of NR System RestorationProcedure

2.1. Introduction to Northern Region Electricity Grid

Northern Region electricity grid is the largest region amongst the fiveregions of the country in terms of geographical area as well as thenumber of constituents. The total effective installed capacity innorthern region, as on 30thNovember 2012 is 57708 MW and the peakdemand during the year 2011-12 was of the order of 40248 MW.

As per the geographical structure of the region, the major generatingsources are located either in the South-Eastern part of the regionconsisting of Super Thermal Power Stations at Singrauli, Rihand andAnpara or in North-Western part of the region consisting of hydrogenerating stations of BBMB, SJVN, THDC, NHPC, KWHEP & ADHPL

& BASPA HEP.

Due to the location of the major generating sources at the extremeends and load centers in the central part of the region, consisting ofDelhi, Haryana, Punjab, Western U.P. and Northern Rajasthan, a largequantum of power flows through the long lengths thereby sometimesresulting in high loading of transmission network with large voltagegradients.

Further, due to a large gap in demand and availability during the peakhours as well as sudden change in weather conditions, at times thesystem parameters undergo wide variations and threaten grid security.All these factors coupled with the equipment failure/faults/mal-operation lead to system contingencies.

During winter season, fog engulfs the whole Northern region whichcauses transient faults in transmission lines leading to systemcontingencies.

2.2. Northern Region System Restoration

Since the Northern Region consists of a large network, in the event ofa total black out, extending start-up power from one end of region to

the other end is rather impractical, and the restoration has to beachieved in a sectionalized manner.

Therefore, based on the geographical boundaries and for ease andspeedy restoration, at the time of black-start the Northern Region isconsidered to have been divided into four different subsystems.

So that in the event of total grid failure, initially each subsystem is to berestored independently as per details given for each subsystem in the


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following chapters. List of Northern Region Sub-System is given atTable1-1

Table 1-1 Northern Region Sub-Systems

Sl. No. Subsystem Name1 Eastern U. P. Subsystem2 North-Central Subsystem3 Rajasthan Sub-System

4Western U. P. / UttarakhandSubsystem

Once the sub-systems are separately built-up, these can besynchronized in stages to integrate into the complete system. For thepurpose of quick understanding and ease of restoration, each chapterhas been further subdivided into following sub-sections:

Sub-system Overview.

Sub-system Restoration Procedure. Sub-system Synchronization. Restoration Stages and Start-up Sequence in a Sub-system.

By following the steps as detailed in the above sub-sections, each ofthe subsystems can be restored independently and thereafter thecomplete system can be integrated in the fastest possible manner.

Exhibit-2A and Exhibit-2B explains the boundaries and thesynchronizing sequence of different subsystems respectively. Theseboundaries have however, been defined on the criteria of most likelyscenario. During the actual operation there can be variations in theabove boundaries and / or sequence, depending upon the real timesituations and other factors, for which NRLDC shall carry out theoverall co-ordination.

Therefore, in the event of a disturbance all the constituents shouldremain in contact with NRLDC for instant exchange of the information,and for carrying out coordinated efforts.

2.3. Restoration of Power Supply to Nuclear Stations

In order to meet the Safety norms of the Nuclear Stations" it is

essential that power supply to the Nuclear Stations be restored onpriority basis. Nuclear Power Plants in the region are as listed below.

1) Narora Atomic Power Plant - 2 x 220 MW,2) Rajasthan Atomic Power Station (A)-1 x 100 MW, 1x 200 MW3) Rajasthan Atomic Power Station (B)-2 x 220 MW.4) Rajasthan Atomic Power Station (C)-2 x 220 MW


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The description of the restoration of different subsystem contained indifferent chapter of this document also contains the steps to be takento for speedy restoration of power supply to the nuclear stations.

2.4. Restoration of power supply to Railway Traction

In the event of system black out, the power supply to Railway Tractionhas to be restored on top most priority. Chapter-7 of this documentexplains the detailed steps to be taken for early restoration of powersupply for Railway Traction.

2.5. Start-Up Power from Western Region

Since major Super Thermal Power Stations in the region, namely;Singrauli (2000 MW), Rihand (3000 MW), Anpara (1630 MW), Anpara-C (1200 MW) and Obra (1442 MW), having a total installed capacity of8272 MW are located in the extreme South - Eastern part of the region,it is very essential that for fast normalization of the system the start-uppower to these stations be extended at the earliest opportunity.

Initially the start-up power to these stations was extended from theRihand hydro station of U.P. or on 132 kV ckt. from Vindhyachal (WR)to Singrauli and Rihand. It has however, been observed that boththese sources are weak and not very much reliable.

Therefore, since February 1997, a provision has been made to availstart-up power from Western Region on 400 kV Vindhyachal ACbypass link. This link was successfully utilized to extend start-up powerto Northern Region during the collapse of Eastern U.P. Subsystem on

01.08.1999 and 22.09.1999 as well as during the failure of thecomplete Northern Regional Grid on 02.01.2001 and its operation hasfound to be satisfactory. Chapter-8 of this document explains the set-up of 400 kV Vindhyachal A.C. by pass link and the steps for itsoperation.

After the establishment of 400 kV Vindhyachal A.C bypass link, the132 kV ckt. from Vindhyachal to Singrauli / Rihand, as mentionedabove can be used as a supplementary link. Similarly the 132 kVcircuit between Singrauli and Rihand (Hydro) which has been looped-in/ looped-out at Renusagar Thermal Station of Hindalco can also beused to supplement the start up functions by availing the supply from

Renusagar as per the agreed arrangement.

2.6. Start-Up Power from Eastern Region

Since December 2008, the Sasaram HVDC Back -to -Back station hasbeen bypassed through an AC bypass link. It is also tested on theHVDC BTB as and when required. Chapter-9 of this documentexplains the set-up of Sasaram 400 kV A.C. Radial Mode operation,and the steps involved in availing black-start Power.


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During grid disturbance on 30th & 31st July 2012, Power Supply wasextended from Easrern Region through following path :

a) 400kV Sasaram-Sarnath lineb) 400kV Muzaffarpur-Gorakhpurc) 400kV Patna / Biharsharif-Balia

Eastern Region supply from Sasaram was extended to Sarnath andAllahabad. From 400kV Sarnath extended to Singrauli STPS, RihandSTPS & Anpara TPS for start up. Supply at 400kV Allahabad wasextended to traction (Railway) supply through 220kV Allahabad.

Eastern Region supply at Muzafffarpur/ Patna/ Biharsharif wasextended to Balia/Gorakhpur. Supply at 400kV Gorakhpur wasextended to 220kV Gorakhpur (UP) and startup given to Tanda TPS.

Supply at 400kV Balia was extended to Lucknow(PG) and start up

power was extended to RosaTPS & Unchahar TPS and traction supplyat Lucknow.

2.7. Load Generation Balance and Spinning Reserve

While restoring the system, besides maintaining load generationbalance, sufficient operative spinning reserve is to be kept in eachsubsystem. All efforts need to be carried out by all the constituents tomaintain the parameters within the subsystem, near nominal values forsecurity of operation of the restored subsystem as well as for ease ofsynchronization.

In order to provide a valuable guidance to maintain a balance betweenload and generation, the estimate of the immediate support/generationlikely to be available in each sub-system vis--vis the essential load tobe met during the system restoration has been explained in each of thechapter under sub-section Subsystem Overview. All the constituentsmust endeavor to maintain a load generation balance in theirrespective areas in line with the details given in this document.

At the same time, it is extremely important that the different generatingunits are operated with free governor mode so as to take smallvariations. In order to control the system parameters and catering anyother eventualities a close monitoring and check is to be maintained onthe different loads, which are energized in the different islands formedafter adisturbance in any subsystem. During system restoration, thefollowing loads are to be met on priority basis:

Survival power or startup power to nuclear power plants. Startup power to thermal power plants. Startup power to non-self starting hydro power plants. Traction power supply Supply to other essential loads such as Hospitals etc.


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Supply to all other customers.

Therefore, while reviving the system, due importance must be given toall above loads. In the document at various places different prioritieshave been shown for the purpose of redundancy and reliability inachieving the target. In order to achieve this objective, at all such

places simultaneous action should be initiated and/or prepared andkept in readiness, so that in the event of difficulties in achieving thetarget through first priority, it may be achieved through the subsequentones without much loss of time.

2.8. Black Start of Gas Stations

NTPC / NCR informed that all Gas Turbines in NCR Region havecapabilities of Black Starting in the event of Grid failure/total blackout.Gas turbines can continue to operate on House-load/ be started andkept on house load operation. Units can be synchronized immediatelyon getting juice from grid. This will help in speedy stabilization of grid

network.As regards charging of lines and associated transformers, gas turbineshave limitation on block load, while charging dead grid. Machines arerun in speed load mode and there are limitations of ramp loading inGas Turbines.

2.9. Voltage Control during build-up of system

Following a blackout, quick restoration of the network is a basicrequirement. This is often constrained by the high voltage levels duringrestoration. In order to ensure that the voltage levels remain at asatisfactory level, the following steps may be taken:

1. Selected generating units may be operated in under-excited mode atlow power levels say less than 5% of full load. This would providesufficient reactive sinks while building up of the system. In the build-upof the Northern Region some of the generating stations where at leastone unit can be operated in such a manner are Rihand (Hy), Obra (Hy,Chibro, Khodri, Ramganga, Bhakra (L), Bhakra (R), Jhakri, Baspa,Bairasiul, Chamera I & II, Salal, RSD, Pong, R.P.Sagar, J.Sagar,Dulhasti, AD hydro and Baglihar.

2. In order to avoid tripping of 220/132 kV, 220/66 kV and 220/33 kV

transformers on over-fluxing, the Tap Changer may be used to controlthis situation by going to the minimum tap position (i.e. more number ofturns).

3. While extending the network, a small load may be switched in at thesubstations before charging any line further.

4. While charging 400 kV lines, reactors (Line/Bus/Tertiary) shall be usedto control the over voltages.


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5. Various reactive power control methods and its impact on the Powersystem are given at annex-II. Ready reckoner for reactive powermanagement is given at annex-IV.

2.10. Monitoring of air pressure at substations

Under a blackout situation, a restoration is often delayed due to thecircuit breakers (CBs) getting locked out on account of low air pressureafter the air compressors trip. This is due to air leakages in the system.Wherever DG sets are provided in the substation, air compressorscould be started immediately and the air pressure are maintained. Inorder to cut down delays in restoration of the system in the event ofcontingencies, the leakages in the compressed air system should bemonitored and checked on a regular basis as a routine check.Furthermore, DG sets, if so far not available, may be provided by theutilities at the substations, at least at all the 400 kV substations and the220 kV substations falling in the trunk route in the system restorationprocedure.

2.11. SCADA system during blackout

It is often observed that following a blackout a large number of realtime data in the SCADA system become suspect. It is mostly causedby failure of auxiliary supply (48 volt DC) to RTUs and communicationsystem (PLCC, Micro Wave /Fiber optic etc.). Due priority may begiven to ensure availability of telemetry at control centers. Systemrestoration becomes much faster with the availability of accurate digitalstatus and analog data.

Stable communication system and proper auxiliary power supply atRTU locations and communication system nodes are essential forfunctioning of SCADA system. The concerned departments lookingafter these systems shall be alerted to take corrective actions in caseof any telemetry failure. Many a times forced polling at RTU locationsquickly reestablishes the link between RTU and control center in caseof a transient fault in the link.

2.12. Mock trials

The restoration procedure would be used only in case of a disturbance

/ blackout. It is important that when there is an actual disturbance allthe players play their respective roles without any problem. As aconfidence building exercise as well as to ensure success in the eventof contingencies, mock trials of certain steps in the restorationprocedure, wherever feasible, need to be done regularly, at least oncein six months. It is suggested that these trials be done at least for thefollowing locations, which would basically involve start-up of a unit, and/ or extension of supply to the adjacent substationas mentioned in thisprocedure. Splitting of buses at substations, wherever possible may


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also be done to facilitate mock trial. Mock black-start exercise has tobe carried out in line with Indian Electricity Grid Code (IEGC) clauses5.2.p, 5.8.a, 5.8.b and other CEA regulations to ensure consistent,reliable and quick restoration in the event of a grid disturbance.

a) Hydro Plants

1. Rihand (Hy) Hydro Plant2. Bhakra Hydro Plant3. Pong Hydro Plant4. Bairasiul Hydro Plant5. Salal Hydro Plant6. Chamera-I Hydro Plant7. Uri Hydro Plant8. Nathpa Jhakri Hydro Plant9. Chibro Hydro Plant10. Khodri Hydro Plant11. Ramganga Hydro Plant12. Rana Pratap Sagar Hydro Plant13. Tehri14. Dhauli Ganga15. AD HPP16. Dulhasti17. Karcham Wangtoo18. Koteshwar19. Chamera-3

b) Gas Power Stations

1. Faridabad (Gas) Plant2. Auraiya (Gas) Plant3. Dadri (Gas) Plant4. Anta (Gas) Plant5. Delhi GTs Plant6. AC Bypass

a. At Vindhyachal HVDC back-to-backb. At Pusauli HVDC back-to-back

2.13. ISLANDING SCHEMEIn order to isolate the healthy subsystems following a large-scaledisturbance, few generating stations/Users and State Utilities have

implemented islanding schemes. Such schemes are in operation inNuclear power Stations of NAPS, RAPS-A and RAPS-B. Islandingschemes have also been envisaged for Delhi and for Kashmirvalley. Details are enclosed as Annex-IX.

Users/utilitie

system restoration procedures dec 12

Documents

system restoration procedures

subsystem overview

subsystem synchronization

uttarakhand subsystem

northern region power

power system network

prefaceindian power

speedy restoration