General Aspects of Restoration

8/3/2019 General Aspects of Restoration

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Definition of Grid Incident as per CEA

Grid Incident is tripping of one or more power system elements of theGrid like a Generator, Transmission Line, Transformer, Shunt Reactor,

Series Capacitor and Static VAR Compensator (SVC), which requires re-

scheduling of Generation or Load, without total loss of supply at a Sub-

Station or loss of integrity of the Grid at 220 kV and above (132 kV and

above in case of North Eastern Region)

Grid Disturbance is tripping of one or more power system elements of

the Grid like a Generator, Transmission Line, Transformer, Shunt

Reactor, Series Capacitor and Static VAR Compensator (SVC),resulting in total power failure or supply at a Sub-Station or loss of

integrity of the Grid, at the level of transmission system at 220 kV and

above ( 132 kV and above in the case of North Eastern Region ).

Definition of Grid Disturbance as per CEA


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TYPE OF GRID INCIDENT

GI 1: Tripping of one or more power system elements of the Grid like a

Generator, Transmission Line, Transformer, Shunt Reactor, Series

Capacitor and Static VAR Compensator (SVC), which requires re-

scheduling of Generation or Load, without total loss of supply at aSub-Station or loss of integrity of the Grid at 220 kV (132 kV in case

of North Eastern Region)

GI 2: Tripping of one or more power system elements of the Grid like a

Generator, Transmission Line, Transformer, Shunt Reactor, Series

Capacitor and Static VAR Compensator (SVC), which requires re-scheduling of Generation or Load, without total loss of supply at a

Sub-Station or loss of integrity of the Grid at 400 kV and above (220

kV and above in case of North Eastern Region)

In increasing order of severity, Grid Incident (GI) is

categorized as


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TYPE OF GRID DISTURBANCE

GD 1: When loss of antecedent generation / load is less than 10% in a

regional Grid

GD 2: When loss of antecedent generation / load is between 10% to less

than 20% in a regional Grid

GD 3: When loss of antecedent generation / load is between 20% to less

than 30% in a regional Grid

GD 4: When loss of antecedent generation / load is between 30% to lessthan 40% in a regional Grid

GD 5: When loss of antecedent generation / load is 40% or more

In increasing order of severity, Grid Disturbances(GD) is categorized as


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Recovery ProceduresRecovery ProceduresA. Detailed plans and procedures for restoration of the regional grid under

partial/total blackout shall be developed by RLDC in consultation with NLDC,

all Users, STU,SLDC, CTU and RPC Secretariat and shall be reviewed /

updated annually.

B. Detailed plans and procedures for restoration after partial/total blackout of each

Users/STU/CTU system within a Region, will be finalized by the concerned

Users/STU/CTU in coordination with the RLDC. The procedure will be

reviewed, confirmed and/or revised once every subsequent year. Mock trial

runs of the procedure for different subsystems shall be carried out by theUsers/CTU/STU at least once every six months under intimation to the RLDC.

Diesel Generator sets for black start would be tested on weekly basis and test

report shall be sent to RLDC on quarterly basis.


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C. List of generating stations with black start facility, inter-State/interregional ties, synchronizing points and essential loads to

be restored on priority, shall be prepared and be available with

NLDC, RLDC and SLDC.

D. The RLDC is authorised during the restoration process following

a black out, to operate with reduced security standards for

voltage and frequency as necessary in order to achieve the fastest

possible recovery of the grid.

E. All communication channels required for restoration process shall

be used for operational communication only, till grid normalcy is

restored.


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Objective

RESTORING NORMAL SYSTEM OPERATION ASQUICKLY AS POSSIBLE

ESTABLISHING ALL INTERCONNECTIONS

RESTORING ESSENTIAL LOADS

SYNCHRONISING OF ATLEAST ONE UNIT AT ALLPOWER STATION

STARTING ALLOCATION OF C. S SHARE

STARTING ECONOMIC DISPATCH

MINIMIZING AMOUNT OF UNSERVED ENERGY


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Possible System Problems

UNITUNIT

FAILUREFAILURE

UNITUNIT

FAILUREFAILURE

INSUFFICIENTINSUFFICIENT

GENERATIONGENERATION

INSUFFICIENTINSUFFICIENT


TRANSFORMER/TRANSFORMER/LINE FAILURELINE FAILURE

LOSS OFLOSS OF

LOADLOAD

LOSS OFLOSS OF

LOADLOAD

REDUCEDREDUCED

NETWORKNETWORK

REDUNDANCYREDUNDANCY

REDUCEDREDUCED

NETWORKNETWORK

REDUNDANCYREDUNDANCY

LINELINEOVERLOADOVERLOAD

OROR

UNSATISFACTUNSATISFACT

ORYORY

BUS VOLTAGEBUS VOLTAGE

LINELINEOVERLOADOVERLOAD

OROR

UNSATISFACTUNSATISFACT

ORYORY

BUS VOLTAGEBUS VOLTAGE

BUSBUS

ISOLATEDISOLATED

LOSS OFLOSS OF


LOSS OFLOSS OF


ISLANDINGISLANDINGISLANDINGISLANDING

SYSTEMSYSTEM

COLLAPSCOLLAPS

EE


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Types of Blackouts

Localized

Partial System Full System With Outside support

Full System Without Outside support

Restoration strategy may be differentRestoration strategy may be different

for each type of outage !for each type of outage !


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Causes of Blackouts

Conditions that could contribute to a system blackout:

Maintenance (Planned & forced) outages

Heavy/Uncontrolled loop flow through system

Changing generation patterns

Weather

Unexpected events/FAULTS

Relay mal-operation

Circuit breaker failure


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Causes of Blackouts

Cascading Thermal over loads Voltage Instability

Dynamic Instability

Load Generation Imbalance

Thermal Limit

Voltage Limit

Stability Limit

Total Transfer capability

Time Horizon

Power Flow


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Causes of Blackouts

Common Sequence of events in blackouts

InitiatingInitiating

EventsEvents

FormatioFormatio

n ofn of

IslandsIslands

SystemSystem

SeparationSeparation

Load /GenerationLoad /GenerationImbalance inImbalance in

islandsislands

Blackout ofBlackout of

IslandsIslands

BeginBeginRestorationRestoration

ProcessProcess


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TIME CONSUMING NATURE OF SWITCHING

OPERATION

START-UP TIMINGS OF THERMAL UNITS

COLD LOAD INRUSH, POWER FACTORS AND

COINCIDENT DEMAND FACTORS

AVAILABILITY OF GOVERNOR FACILITIES OF

UNITS

Common Concerns


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Problems /Constraints

RE-ASSEMBLING TIE ELEMENTS OF POWER

SYSTEM.

IMPAIRED COMMUNICATIONS,LIMITED

INFORMATION.

NON-AVAILABILITY OF SCADA/EMS

APPLICATION SYSTEM.

UNFAMILIARITY WITH THE SITUATION(DOES NOT OCCUR REGULARLY)

TIME CONSTRAINTS


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Restoration Tasks

INITIAL ASSESSMENT

SYSTEM STATUS DETERMINATION

PLANT PREPARATIONSERVICES/START-UP

NETWORK PREPARATION

NETWORK ENERGISATION LOAD RESTORATION

SYSTEM REBUILDING


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INITIAL COURSE OF ACTION

Assess extent of black out

Check whether any sub-system/island is alive or not

Check the interconnection with other region(s)

Appraise the severity of disturbance to all concerned

Chalk out the optimum path for restoration

Defer all planned outage as per IEGC 5.74 (g)

Power Station /

Sub-station

Open all circuit breakers

Note relay indications and reset them

Check for damage or technical snag

developed at any element

RLDC


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Important Considerations during RestorationRLDC / SLDC

Generating Stations having black-startfacilities start up immediately.

Generation availability in each island / subsystem to be ensured

Transmission lines available in theinterconnection between islands / sub

systems to be ensured.

Coordinate the load pick-ups with theramp rate of generation to maintain

sustainable frequency (around 50 Hz) .

Proper coordinationbefore

synchronization of two islands

Risky synchronization should beavoided

Load to be added in small steps withsmaller and radial loads preceding

larger load.

Restoration work should be shared &coordinated among the shift

personnel

Shift personnel should preferably beretained till restoration is over

Shift personnel of sub/power-stationshall be promptly formulated the

restoration strategy to be adopted


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Power / Sub-Station

Important Considerations during Restoration

Governor and AVR are to be kept in

manual mode, if required

A reasonable active to reactive power

ratio is to be maintained to operate the

machine normally

Auxiliary power to be readily

available

Total auxiliary power drawn is to be

kept within 3% of the sources

capacity

Ascertain whether machines can

supply the power, while releasing

loads

Tap Position of Transformer,

Bus Voltage and frequency shall

be closely monitored to avertover fluxing

UFRs, SPS, UVR to be kept

deactivated


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Special Consideration in extending/availing start up power

Power Plant Operators should be able to differentiate between

Full auxiliary power needed to start all machines

Minimum auxiliary power needed to start a minimumnumber of machines

Considerations to be kept in mind for availing start up power

Nearness to the source 132 kV lines vis --vis 220 kV/ 400 kV lines

Shorter route having a number of intermediate sub-stations

Longer route having very few/ no intermediate sub-stations


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Clear-cut authority should be given to SLDC for extending start

up power from one sub-system to another sub-system or from one

constituent to another constituent as

oLine through which start up power is to be extended

oQuantum of such start up power

oNormal time period admissible Concerned SLDC should also be empowered to resort to load

shedding or bring up additional generation wherever possible, to

extend start up power to neighboring subsystems/constituentsduring the period of crisis.

Special Consideration in extending/availing start up power


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SOME DONTS

Do not panic

Do not load any generator beyond

80% of its capacity

Do not load any line/ICT beyond80% of its capacity

Do not hastily connect loads andensure that the island / sub-system

frequency be within sustainable

range

Extended power should not bewithdrawn except in case of extreme

emergency and without intimation to

RLDC

No communication disputes should beraised during the restoration period.

Load dispatch centers should not bedisturbed while discharging their duties

and expected to function as Management

information system.


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Restoration Process

Bottom-up/Build-up StrategyBottom-up/Build-up StrategySteps involved in the Bottom-up Strategy

Select units to black-start.

Start and stabilize black-start units.

Determine restoration transmission path.

Begin expanding island(s) by restoringtransmission and load.

Synchronize island(s) when appropriate.


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Build-up StrategyMultiple island Method of Restoration


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Build-up StrategyCore island Method of Restoration


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Build-up Strategy

Backbone island Method ofRestoration


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Restoration Process

Restore backbone transmission system, usually from

outside assistance. Restore critical generating station and substation load

from transmission system.

Bring more generation. Restore underlying transmission system.

Continue restoring load.

p-down / Build down strategy


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Build-Down Strategy

Core island Method of Restoration


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Combination Approach

Combines the Build-up and Build-down

approach.

Steps in this approach include:Restoring transmission from an outside source at the

same time as building islands of generation.

Interconnecting islands with each other or outside

source when able.


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Selection of Restoration

Strategy

Restoration method chosen depends on:

Extent of blackout

Availability of outside assistance

Availability of internal black-start generation

Utility philosophy/procedure


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Load Restoration

Priority load for restoration

Generating Unit auxiliary power

Nuclear Station auxiliary power

Substation light and power

Traction Supplies

Supply to Collieries Natural gas or oil supply facilities


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POWER STATION INSTALLEDCAPACITY

(MW)

UNITTYPE

START UPFACILITY

BLACK STARTFACILITY

SOURCE CAPACITYin

kVA

KHANDONG 2*25 HYDRO DG SET 1X250 YES

KHANDONG (KOPILI STII)

25 HYDRO DG SET 1X125 YES

KOPILI

4*50 HYDRO DG SET 1X600 YES

DOYANG 3*25 HYDRO DG SET 2X625 YES

RANGANADI 3*135 HYDRO DG SET 1x500 YES

R. C. NAGAR 4*21 GAS DG SET 1X250 YES

KATHALGURI 4*33.66+2*35+3*30

GAS+STEAM DG SET 1X950;1X250

NO

ISGS : NEEPCO

contd

ISGS : NHPC


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POWER STATION INSTALLEDCAPACITY(MW)

UNITTYPE

START UPFACILITY

BLACK STARTFACILITY

SOURCE CAPACITYin

kVA

LOKTAK 3*35 HYDRO DG SET 2X315 YES

ISGS : NHPC


UNITTYPE

START UPFACILITY

BLACK STARTFACILITY

SOURCE CAPACITY inkVA

NAMRUP 3*23+12.5+30+22 GAS DG SET 844 YES

LAKWA 4*15+3*20 GAS NO NO NO

ADAMTILA(IPP-DLF)

3*3+5 GAS GRIDPOWER

NA NO

BASKANDI 3*3.5 GAS GRIDPOWER

NA NO

KARBI LANGPI 2*50 HYDRO DG SET 1X500 YES

STATE : ASSAM

contd


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UNITTYPE

START UPFACILITY

BLACK STARTFACILITY

SOURCE CAPACITY in

Volt

UMIUM ST I 4*9 HYDRO BatteryBank

110 YES

UMIUM ST II 2*9 HYDRO BatteryBank

110 YES

UMIUM ST III 2*30 HYDRO BatteryBank

110 YES

UMIUM ST IV 2*30 HYDRO Battery

Bank

220 YES

UMTRU 4*2.8 HYDRO BatteryBank

110 YES

STATE : MEGHALAYA

contd


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UNITTYPE

START UPFACILITY

BLACK STARTFACILITY

SOURCE CAPACITY inkVA

GUMTI 3*5 HYDRO NO NO NO

BARAMURA 2*5+6.5+21 GAS DG SET 1X380 YES

ROKHIA 6*8+21 GAS DG SET 2X380 YES

STATE : TRIPURA


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Synchronizing facilities at power

stations / major Sub-Stations

in NER


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SUB-STATIONS VOLTAGELEVEL

(kV)

SYNCHRONISINGFACILITY

DG SETDETAILS

in kVA

HALFLONG 132 YES 1X63

AIZWAL 132 YES 1X63

KUMARGHAT 132 YES(NOT OPERATIONAL) 1X63

BADARPUR 132 YES 1X100

KHLIEHRIAT 132 YES 1X100

NIRJULI 132 YES 1X100

ZIRO 132 YES 1X100

contd

CTU : POWERGRID


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(kV)


DG SETDETAILS

inkVA

BTPS 220 YES NO

SARUSAJAI 220 YES NO

SAMAGURI 220 YES(NOT OPERATIONAL) NO

MARIANI 220 YES NO

TINSUKIA 220 YES NO

KAHELIPARA 132 YES 1X30

DEPOTA 132 YES(NOT OPERATIONAL) NO

STATE : ASSAM

contd


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(kV)


79 TILLA(AGARTALA)

132 YES

STATE : TRIPURA


(kV)


UMIUM STG-I 132 YES

UMIUM STG-III 132 YES

STATE : MEGHALAYA


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General Aspects of Restoration

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