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The black start procedures should contain the

fol lowing minimum detai ls.1. Generation Securing

2. Generation build-up

Survival and Start-up Power of Power Plant(s).

Power Station(s) with Black-start facility.

3. Build-up of islands

4. List of black start facilities, inter-state/regional ties, synchronizing points and essential

loads to be restored on priority

5. Detailed State/Utility-wise Restoration

plans


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SYSTEM RESTORATION APPROACHES

1. In systems with a fair dispersal of Generating stations with black start

facilities, those generating stations where black start facilities are available,

should be started up and islands formed around these generating stations by

connecting essential loads. These islands are then interconnected at predefined

locations where synchronizing facilities are available. The speed of restoration

enhances with increase in number of black start facilities and their dispersal.

Gujarat, Chhattisgarh and M.P have considerable number of black start facilitieswhile Maharashtra suffers from lack of adequate number of black start

generators. It is required to carefully monitor the operation of the island (re-

integration with rest of the grid) due to small stiffness in islands. One engineer

shall be specifically assigned to monitor one island.

2. While adding loads, care should be taken to ensure step by step

addition keeping in view load characteristics, ie., variation of load with respect

to voltage and frequency and stiffness of island. During cold load pick up

sudden starting of motor loads or power plant auxiliaries like BFP, PA fan etc.,can cause voltage dips due to drawal of high starting currents. Essential loads

can be restarted in steps smaller than 5 MW. It is preferable to restore rotating

type loads which co~tributes to inertia of the island. In any case, load pick up

should not cause frequency excursions greater than 0.5 Hz in the island.

3. The second approach could be followed in case self start facilities

are available at only a few power stations or the stqrt up power has to be

imported from neighbouring regions at one0or two points. In this approach, the

start up power required to be extended to all the generating stations on prioritybasis while restoring few loads and transformers for voltage control. The start

up power available from neighbouring regions at various interconnections have

to be seriously explored since considerable assistance can be availed and the

restored system is connected to stable external systems. The procedures have to

be laid down for quickly harnessing these facilities.

The restoration through this approach could be delayed due to problems in

charging the lines, high voltage, lack of synchronising equipment at certain

substations etc. and may involve system disturbances during restoration.


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OPERATIONAL GUIDELINES.

1. Each SLDC will coordinate synchronisation of

units and transmission lines in its system in consultation with

WRLDC. For ISGS power stations , WRLDC will becoordinating for their synchronisation. WRLDC will

coordinate interstate/ inter-regional startup power availability

and also inter-state/inter-regionql synchronisation of the

system.

2. Minimum 25 MW power flow from West toNorth will be maintained on HVDC back to back link at

Vindhyachal during normal operating condition.

3. Black start generation usage priorities:-

a) provide startup power to hot units

b) provide startup power to units that are cool; but capableof rapid restart

c) restore stations auxiliary service to generating

stations0and sub-stations.

d) Pick up essential loads.

4. Transmission corridors used for startup power

should be isolated from any damaged/faulty equipment and

are of minimum length and minimum voltage level to reduce

line charging.

5. The constituent receiving assistance during

restoration process should restrict to the agreed quantum only

since this may have an adverse effect on healthysystem0rendering the assistance.


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GENERAL GUIDELINES

While each disturbance would be different and may require a different plan,

nevertheless it would be useful to formulate general guidelines for the benefit

of the load despatchers. These may be described as0below:

i. The operators at generating stations and substations should have the

knowledge of pre-planned synchronising locations and synchronising

procedures. Synchronising should be done preferably at generating stations.

ii. Switching procedures should be clearly laid down and periodicallyreviewed.

iii. The part systems should be reintegrated only after adequate

stabilization.

iv. The transformer taps should be checked for desired settings to

minimise voltage difference.

v. The substation operators and load despatchers sxould make a check of

the capacitor banks and reactors in service and accordingly to carry out the

switching operations for voltage control.vi. Energising long high voltage lines and cables should be avoided until

enough generating capacity is available.

vii. Provision of islanding schemes area-wise, power station-wise and unit-

wise would enhance the ability to restore faster. These should be fully

exploited.

viii. Some of the generating units might have been saved due to successful

islanding. Stabilization of such online generation is of top most priority.

ix. Provision of start up power to nuclear plants should be given priority aspoisoning of the reactors would delay restoration of nuclear units.

x. In case of failure of main communication channels, guidelines for

decision making should be given to all the major substations and generating

stations.

xi. Devising islands for power stations wherever small units could help in

faster restoration of the grid are available. One small unit at these power

stations can be islanded with radial loads and/or house load.


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REQUIREMENT OF SURVIVAL POWER /AUXILIARY POWER

Survival power can be defined as the powerneeded for avoiding the damage to the equipmentin case of supply failure. This power is requiredfor

Turbine emergency oil pump Jacking oil pumps Barring gear of the turbines Lubricating oil pumps Compressors for ABCB operation Emergency lighting Battery chargers of units, station, and

communication and telemetry system

The survival power required by 120 MW units isof the order of 250-350 kW while the requirementof 210 MW units is of the order of 350-500 KW.As a general rule, the survival power requirementwould be around 0.25-0.30% of the unit capacity.Nuclear power plants should be supplied withsurvival power on priority basis.


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REQUIREMENT OF START UP POWER

The start-up power is the power required for the

auxiliaries while the generating unit is restored. Therequirement of start-up power by various units is asfollows:-

Nuclear & : 7 to 8% of the unit capacityThermal

Hydro : 0.5 to 1% of the unitcapacity

Gas : 1.5 to 2% of the unitcapacity.


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Ukai (H) 4 x 75 Hydro Diesel 500 KVA One 75 MW

gen. house set

Mini Hydro 2 x 2.5 Hydro Diesel 50 KW

Kadana 4 x 60 Hydro Diesel 500 KVA

Dhuvaran 1 x 27

+ 4 x 63.5

+ 2 x 140

Gas

Thermal

Any one

unit out of

the units

1,2,3 & 4

1 x 63.5

MW

Islanding of

any one units

out of units 1,

2, 3, & 4 on to

house load

Diesel 1600 KVA

x2

700 KVA

GIPCL 3 x 32

+ 1 x45

+ 1x104

+ 1x5

Gas

Steam

Gas

Steam

All units

Diesel

141 MW

500 KVA

Islanding of

all units

A.E.Co.

Stn. C

Stn. D,E,F

4 x 15

2 x 30

3 x 110

Thermal

Thermal

Thermal

Stn-C

islands

Diesel

30 MW

500 KVA

Islanding of

0ne 30 MW

unit

GPEC 3x 138 Thermal Diesel 3000 KVA

Kawas 4 x 106

2 x 116

Gas Diesel 2700 KW

Gandhar 3 x 144

+ 1x225

Gas Diesel 3120 KW

CCPP, Vatwa 3 x 39+ 1 x 45

Gas

Essar


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wer Station Installed

Cap. (MW)

Survival

power

Auxiliary

Power

Diesel

Capacity

Synch. Facl.

B

ai (Hy) 4 x 75 100 KW 250 KW 500 KVA Yes

ai LBCH 2 x 2.5 5 KW 20 KW 50 KW Yes

dana (Hy) 4 x 60 7 KW 200 / 250 KW 500 KVA Yes

ai (Th) 2 x 120

+ 1 x 200

+ 2 x 210

1.447

MW

4.5/ 8 MW - Yes

ka (Th) 2 x 120 500 KW 12 MW 500 KW Yes

uvaran (Th) 1 x 27

+ 4x63.5

+ 2x140

500 KW 5 MW 500 KW Yes

ndhinagar 2 x 120+ 3 x 210

175/350KW P.U

7.2/10.7 MWP.U

500 KVAD.G.set

under

erection

Yes

nakbori 7 x 210 0.8 MW 13 MW P.U 3x400

KW

Yes

nandro 2 x70+1x75 360 KW 4.5 MW 1280 KW

& 500KW

Yes

E.Co

Stn. C 2 x 30 250 KVA 9 MW 1x500

KVA

Yes

D,E,F, + 3x110 2 x 125

KVA

+ 3x33

s 3 x 32 Nil 350 KVA 1x500

KVA

Yes


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1. REACTIVE POWER BALANCE

Objective

To keep system voltage within allowable range

Strategies

Energising fewer high voltage lines Operating generators at minimum voltagelevels (logging p.f) Deactivate switchable capacity Connect shunt reactors and tertiary reactors

Adjustment of transformer taps Pick up loads with lagging p.f Charge more transformers Charge shorter lines Operating synchronous condensers / SVCswhere available Avoid charging lines with series capacitors

Concerns

Self excitation of generators and run away

voltage rise.


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2 LOAD AND GENERATION BALANCE

Objective

To maintain system frequency within allowablelimits

Strategies

Restore loads in small increments (minimum &

essential) Smaller and radial loads to be restored prior tolarger and network loads Feeders with U/F relays are restored later (bypassuntil frequency stabilizes) Load restoration based on load characteristics

To get adequate inductive loading to compensatecapacitive effect while charging high voltage long line,a concentrated load of large town/city should bereleased along with that of Railways. Maintain frequency close to 50 Hz paying specialattention to traction and other fluctuating loads

Concerns

Size of load pick up depends upon the rate ofresponse of prime movers Load pick up in large increments led to collapse ofthe restored systemsTwice in Gujarat on 9.12.95Twice in Maharashtra on 9.12.95Once in MP on 9.12.95


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3 LOAD AND GENERATION CO-

ORDINATION PRIORITIES

Restart Stage

Priority to restore power supply to generatingstations and load dispatch centers. Priority to supply start up power to hydro andgas units Priority for providing backup/survival/startup

power to nuclear power stations Several load and generation islands formed Black starting of small hydro or gas units In each island, the objective is to supplystation auxiliary power and start up power The number of islands limited by sources of

black start units Each island should preferably be monitored

by one load despatcher till reintegration.

Re-integration stage

Load restoration stagevIn small stepsvObserve frequency charges (< 0.5 Hz) with loadadditionvPreferable to restore rotating type loads if

possiblevCold load pick up is the main concern


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4 MONITORING & CONTROL

Location of the fault and extent ofcollapse of the system should beascertained before restoration

It is dangerous to restore a faulty lineor faulty equipment

Ensure communication links between

control centers, power plants and sub-stations

SCADA system performanceInadequate displaysExcessive alarms

Protection tele-meteringEMS


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5 Communications

Establishing communication

between LDCs, Generating Stations

and major substations.

All important substations only to be

kept in touch with and links with

unimportant substations to0be cut off

to avoid draining of batteries. All communication channels

required for restoration process shall

be used for operatyonal

communication only till grid normalcy

is restored (IEGC 6.8.e)


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6 PROTECTIVE SYSTEMS /

SYNCHRONISATION

Check all interlocks

Sort out problems in closing of breakers dueto low gas/air pressure Avoid paralleling islands through weak ties. Synchronizing facilities at sub-stations Standing phase angles to be checked anddifference reduced by generation control.Synchronisation only through synchro-checkrelays Try to synchronise islands or part systems,

near the generating stations requires less co-ordination and easier to control Operate generators on lagging p.f Generators supplying start up power shouldnot be loaded beyond 80% The capacity of the island to sustain the

starting current of BFPs should be checked If sub-systems are to be synchronized awayfrom generating stations, be extremely cautiousof standing phase angle differences (systemoccurrence on 28.4.93 in Maharashtra)


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7 ENERGY STORAGE

Loss of back up power supplies like:

BatteriesBattery chargersUPSDiesel sets

Could affect

Operation of circuit breakers Motor operated isolators Communication SCADA

(one of the important causes of delays inrestoration)


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8 SWITCHING OVER VOLTAGES

Energise small sections of lines Energise lower voltage lines In case of parallel circuits, energise one ckt. Control high voltages during restoration to

avoid damage of Las/CVTs et.

9 Survival Power

Ensuring availability of back up power supplies such

as batteries, battery chargers, D.G sets to avoid effect

on non operation of circuit breakers, communication

systems etc., which can cause delay in restoration.

10 Awareness of Restoration Plans

Training and necessary documentation may be

provided to Load Despatchers by respective LDCs.

11 Exchange of Information

Exchange of information among SLDCs and between

RLDC and SLDCs is essential for proper co-

ordination.


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12 SYSTEM STUDIES FOR MAKINGRESTORATION PLANS

1 Power flow

Multiple islands Study voltage problems

Generator excitation limits Transformer taps

2 Dynamic stability

To study load generation co-ordination While load pick up, generation responsecould be studied

3 EMTP

To determine what lines to be charged Transient over voltages in switching


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13. RESTORATION PLAN

v Identification of collapsed powersystem components and equipment.

v Restart and supply start up power firstto hydro and gas stations

v Startup power to thermal stations,auxiliary power to sub-stations

v Co-ordination of power plant start upwith load pick up to bring generators totheir stable minimum generation levels

v Restore in sub-systems if multiple

sources of startup power available

v Energising transmission lines withacceptable transient and sustained overvoltages

v While load pick up, check frequencydecline

v Reintegration of sub-systems

v Ensure discipline and avoid overdrawals until proper stabilization


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14. ROLE OF LOAD DESPATCH CENTRES

v Determine severity of collapse

v Identify and initiate black start facilitiesv Import start up power from

neighbouring states or regionsv Import more power to meet essential

loads from neighbouring states or regionsv Decision making and guidancev Determine priority loadsv

Check unbalanced loading due to tractionv Getting start up power from captivepower plants, if possible

v Ensure communication links, SCADAfacilities

v Guidance to sub-station/generating

station operators from the results of EMSv Identify points of reintegration and

synchronizationv Reporting


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15. TRAINING AND ROUTINE EXERCISES

v Short time appreciation courses

v Review of targets for restoration as

soon as a black start facility or inter-state /inter-regional connection is stabilized.

v Review of restoration plants after everyoccurrence

v Updating of restoration manually andother documentation

v The strategies of restoration should havealternatives to enable flexibility

v Training by experts

v Interactive training and case studies

v All constituents should participate intraining programmes

v Formation of a command group

v Mock exercises

v Preparation of manuals on importanttelephone numbers etc.


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16. OVER VOLTAGE CONTROL DURING

RESTORATION

(A) Sustained power frequency overvoltages

v Due to lightly loaded linesv May cause under excitation ofgeneratorsv May lead to self excitation ofgeneratorsv Over fluxing of transformers

(generate harmonic distortions and causetransformer over heating)

(B) Transient voltage or switching surges

v caused by energisation and de-

energisation of linesorv switching of capacitive elementsv In conjunction with sustained o/v maycause arrestor failures


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Harmonic Resonance Voltages

v Oscillatory un damped or weaklydampedv

Of long durationv Originate from equipment nonlinearities and switching natural frequency ofseries resonance circuit formed by sourceinductance and line charging capacitance.v Magnetizing in rush due to transformer

energisationv Lightly damped due to light loading oflinesv Over fluxing of transformers (beyond1.1 pu)

2. Equipment limitations

Transformers and Arrestors

1.2 p.u for one minute

1.4 p.u for 10 seconds

Circuit breakers

v Will have reduced interruptingcapability

v Can interrupt line charging currentsupto 1.2 p.u


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3. Control of sustained over voltages

v Sufficient under excitationcapability on the generators

v Connect lagging p.f loads andshunt reactors

v Remove all sources of reactivepower and switch off capacitor banks

v Run generators at maximumpossible reactive power output to allow

margin to adjust for large chargingreactive power during line switching

v Tap staggering of transformers

v Avoid extra parallel lines

v Maintain low voltage profile onthe lines to reduce line charging


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4. Control of switching transients

v Switching o/v may cause flash over anddamage to equipment

v Switching transients on fast transient causedby ill timed closure of breakers

v To be controlled to 2.5 p.u for 400kV and 1.9p.u for 800kV and 2.3 p.u for others

v Usually of fast front, low energy or slow front,high energy transients.

v Keep steady state voltage below 1.2 p.u. Keep

generator terminal voltage around 0.8 p.u


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5. Harmonic Resonance

vTransformers may get over excited and

generate harmonicsvCombination of system inductance and linecapacitance forms a series resonance circuit whichis excited by harmonic distortions produced bytransformer saturationv

Harmonics generated by magnetic current inrush can also lead to harmonic resonancevSufficient load to be connected to theunderlying system at both ends to damposcillationsvLower order resonances produce higher over

voltages(3rd, 4th, 5th, 6thharmonics)vTo control over voltage due to transformer overexcitation, user lower taps (system studies)vHarmonic resonance can be damped byconnecting loads at both endsvConnect dead load on the transformer to beenergizedvReduce number of highly loaded lines (inparallel paths)

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