Optimizing Power System Optimizing Power System Restoration Resources and Restoration Resources and

Actions Actions

ChenChen--Ching LiuChing LiuElectrical and Computer EngineeringElectrical and Computer Engineering

Iowa State UniversityIowa State University

PSERC Research Tele-seminar, November 2006

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State of the Art

•• Primarily manual work by Primarily manual work by operatorsoperators

•• Off line restoration planningOff line restoration planning•• Little progress has been made on Little progress has been made on

system restoration methodology system restoration methodology •• On line implementation limitedOn line implementation limited•• Literature Literature

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System Restoration Stages

Load restoration is only a means to an end

Load restoration is the objective

PREPARATIONActions are time-critical

SYSTEMRESTORATION

LOAD RESTORATION

30-60 minutes

3-4 hours

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System Restoration Tasks

•• Knowing status of the grid Knowing status of the grid •• Maximizing generation capabilities Maximizing generation capabilities

with the available black start resourceswith the available black start resources•• Scheduling of tasks and resources during Scheduling of tasks and resources during

system restorationsystem restoration•• Establishing transmission capability Establishing transmission capability

and paths while meeting operating and paths while meeting operating constraintsconstraints

•• Picking up load while meeting Picking up load while meeting operating constraints and load operating constraints and load requirementsrequirements

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Example Restoration Strategies

•• BuildBuild--upwardupward•• BuildBuild--downwarddownward•• Other variationsOther variations

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First Stage

•• Basic operations common to all Basic operations common to all strategiesstrategies

•• SubSub--processes defining early processes defining early stages of restoration processstages of restoration process

•• Minimal configuration of Minimal configuration of autonomous stable source with autonomous stable source with necessary transmissionnecessary transmission

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Restoration Building Blocks

•• May include nonMay include non--autonomous autonomous BTG, connection transmission, BTG, connection transmission, necessary compensation & load necessary compensation & load blocksblocks

•• Associated with schedule of Associated with schedule of switching & control actionsswitching & control actions

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Second StageTarget System

•• System state achieved by end of System state achieved by end of restoration processrestoration process

•• May not be preMay not be pre--disturbance disturbance systemsystem

•• Restrict set of postRestrict set of post--restoration restoration configurationsconfigurations

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Restoration Constraints

•• Physical constraintsPhysical constraints•• Scheduling constraintsScheduling constraints•• Policy constraintsPolicy constraints

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Third Stage

Load Restoration Load Restoration –– Pick Up LoadsPick Up Loads

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BLACK-START UNIT OPERATION

NON-BLACK-START UNIT OPERATION

STATICMVAR

INSPECTION

STABILITYINSPECTION

SWITCHINGSEQUENCE INSPECTION

TRANSIENTVOLTAGEINSPECTION

CAPACITYINSPECTION

FAULTINSPECTION

MAN-POWER DISPATCH

FUEL INSPECTION

MECHANICAL INSPECTION

SYSTEM RESTORATION

LOAD MANAGEMENT

MW MANAGEMENT

MVAR MANAGEMENT

PATH MANAGEMENT

Restoration Strategy

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Example – Generation Capabilities

(4 Different Generating Units)(4 Different Generating Units)

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Example – Optimal Starting Sequence

MW

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Cranking Priorities

•• Units with critical maximum Units with critical maximum intervalinterval

•• Critical max interval units with Critical max interval units with most urgent time constraint most urgent time constraint

•• Units that can generate highest Units that can generate highest MWH within a given period MWH within a given period

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Unit Type MW Cap. Ramp. rate Crank to paral. Crit. max. int. Crit. min. int. Startup req.(MW) (MW/hr) (hr) (hr) (hr) (MW)

Chester_4 CT 15 40 0 N/A N/A 0Chester_5 CT 15 40 0 N/A N/A 0Chester_6 CT 15 40 0 N/A N/A 0Chester_7-9 CT 45 120 0 N/A N/A 0Conowingo_1-7 Hydro 200 200 0 N/A N/A 0Conowingo_8-11 Hydro 200 200 0 N/A N/A 0Cromby_1 Steam 180 80 1:40 N/A N/A 8Cromby_2 Steam 180 80 1:40 N/A N/A 8Croydon_1 CT 300 120 0:30 N/A 5:00 6Delaware_7 Steam 130 60 2:40 3:20 N/A 5Delaware_8 Steam 130 60 2:40 3:20 N/A 5Delaware_9-10 CT 30 90 0 N/A N/A 0Delaware_11-12 CT 30 90 0 N/A N/A 0Eddystone_1 Steam 150 40 1:40 N/A 3:20 12Eddystone_2 Steam 150 40 1:40 N/A 3:20 12Eddystone_3 Steam 150 40 1:40 N/A 3:20 12Eddystone_4 Steam 150 40 1:40 N/A 3:20 12Eddystone_10 CT 15 45 0 N/A N/A 0Eddystone_20 CT 15 45 0 N/A N/A 0Eddystone_30-40 CT 30 90 0 N/A N/A 0Falls_1-3 CT 45 135 0 N/A N/A 0Moser_1 CT 30 90 0 N/A N/A 0Muddy Run_1-4 Hydro 400 150 0:30 N/A N/A 6.6Muddy Run_5-8 Hydro 400 150 0:30 N/A N/A 6.6Richmond_3 CT 50 100 0 N/A N/A 0Richmond_4 CT 50 100 0 N/A N/A 0Schuylkill_1 Steam 135 135 2:00 2:30 N/A 2.7Schuylkill_3 Steam 135 135 2:00 2:30 N/A 2.7S h lkill 10 CT 15 45 0 N/A N/A 0

. . . . . .

Ramping Rate Ramping Rate

Critical Min. Interval Critical Min. Interval

Critical Max. IntervalCritical Max. Interval

PECO-Energy Generating Units

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MW Capability Curves

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TIE LINEUTILIZATION

BLACK-START UNIT OPERATION

NON-BLACK-START UNIT OPERATION

STATICMVAR

INSPECTION

STABILITYINSPECTION

SWITCHINGSEQUENCE INSPECTION

TRANSIENTVOLTAGEINSPECTION

CAPACITYINSPECTION

FAULTINSPECTION

MAN-POWER DISPATCH

FUEL INSPECTION

MECHANICAL INSPECTION

SYSTEM RESTORATION

LOAD MANAGEMENT

MW MANAGEMENT

MVAR MANAGEMENT

PATH MANAGEMENT

TIE LINEUTILIZATION

Restoration Strategy with Tie Lines

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Check If There Is a Path Between Them

System Restoration

LoadManagement

Tie LineUtilization

MWManagement

Check If a Tie Line Can Crank an NBS Unit

Check If Tie Line Can Provide Enough Cranking Power

Negotiate for More Power Import

Check If Enough Load Can Be Found

Negotiate for Less Power Import

PathManagement

Crank NBS Units

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Check If System Can Provide Enough Power

System Restoration

LoadManagement

Tie LineUtilization

MWManagement

Respond to Tie Line Request

Decide Priorityof Tie Line

CheckLoad RestorationCondition

Check NBS UnitsRestartCondition

PathManagement

Negotiate for Less Power Export

Check Trans-mission Capacity

MVARManagement

Respond to Request

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Check ifThere AreTrans-missionPaths

System Restoration

LoadManagement

Tie LineUtilization

MWManagement

Check if a Tie Line Can Serve Loads

Check ifTie LineCanProvideEnoughPower

Check ifEnoughLoadCan BeFound

PathManagement

MVARManagement

Negotiatefor MorepowerImport

Consider UsingTie LineInstead of SystemGeneration

Negotiatefor LessPowerImport

Serve Load

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S1

TLi

TLe

Internal Unitsto be Cranked by TLi

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S2

TLi

TLe

Internal Unitsto Provide TLe - TLi

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CT

TLi

TLe

S3

Cranking Paths Affected

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G1

G2

G3

Induced MWh Increase

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MWh Increase by S1Increase from Earlier Startup of S1Increase Induced by S1

MWh Decrease by S2 (S3)Decrease from Delayed Startup of S2 (S3)

Decrease Induced by S2 (S3)

Tie Line Utilization

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5678 1234MUDDY RUN

PEACH BOTTOM

CONOWINGO124567 8 9 10 113

CROMBY

Test Subsystem

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Min after blackout

0

500

1000

1500

2000

2500

3000

3500

0 100 200 300 400 500 600

Without PeachBottom

With PeachBottom

System Generation Capability

MW

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Min after blackout

MW

0

500

1000

1500

2000

2500

3000

3500

0 100 200 300 400 500 600

0MW

10MW

50MW & 100MW

System Generation Capability

From Peach Bottom

MW

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Generic Restoration Actions (GRAs)

•• start_black_start_unit (X)start_black_start_unit (X)•• find_path (X,Y)find_path (X,Y)•• energize_line (X)energize_line (X)•• pick_up_load (X)pick_up_load (X)•• synchronize (X,Y)synchronize (X,Y)•• connect_tie_line (X)connect_tie_line (X)•• crank_unit (X)crank_unit (X)•• energize_busbarenergize_busbar (X)(X)

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Using GRAs to Construct RBBs

NBSBS

B1B2

B3

L1 L2C1

C2

C3

S1

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Using GRAs to Construct RBBs

•• Find transmission path between Find transmission path between BS & NBSBS & NBS

•• Start blackStart black--start unit BSstart unit BS•• Build transmission path from Build transmission path from

busbarbusbar B1 to B3 and pick up loads B1 to B3 and pick up loads for stabilizationfor stabilization

•• Crank nonCrank non--blackblack--start unit NBSstart unit NBS

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Using RBBs & GRAs to Build Restoration

Strategies

NBS

BS1

B1

B2B3

L1

L2

L3C1a

C2a C3

BS2

C1b

C2b

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Using RBBs & GRAs to Build Restoration

Strategies•• Select Two Select Two RBBsRBBs

–– RBB1: Use BS1 to energize B1RBB1: Use BS1 to energize B1–– RBB2: Use BS2 to energize B2RBB2: Use BS2 to energize B2

•• Build RBB1Build RBB1–– Prepare loadPrepare load–– Start BS unitStart BS unit–– Energize busEnergize bus

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Using RBBs & GRAs to Build Restoration Strategies (Cont.)

•• Build RBB2Build RBB2•• Energize ringEnergize ring•• Restart nonRestart non--blackblack--start unit NBSstart unit NBS•• Pick up loads along ringPick up loads along ring

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Petri Net Algorithm to Optimize Sequence of GRAs

TL1

Bus2

Bus1

Bus3

L1

L2 L3

Line1-2

Line2-3

Line3-1

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Petri Net Model

P1 P2

P8

T1

T2

P15

T15

P16

P22

P25

T14

P14 P3 P9 P4

T3T4 T5

P17

T16

P21

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Schulykill-SouthwarkSubsystem

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Time to Complete GRAs

1010Pick up LoadPick up Load

2020Synchronize between Synchronize between BusbarsBusbars/Lines/Lines

1515Crank a NBSUCrank a NBSU2525Connect Tie LineConnect Tie Line

55Energize Energize BusbarBusbar from from BSU/BSU/busbarbusbar/line/line

1515Restart BSURestart BSU

Time (Time (minsmins.).)Generic Restoration Generic Restoration Action (GRA)Action (GRA)

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Sequence of Actions for Schuylkill-Southwark

============================================================Time (min.) ActionsTime (min.) Actions----------------------------------------------------------------------------------------------------------Restoration Building Block 1:Restoration Building Block 1:

0 Connect BSU CT100 Connect BSU CT1015 Energize bs2 from CT1015 Energize bs2 from CT1020 Energize bs3 from bs220 Energize bs3 from bs225 Energize bs4 from bs325 Energize bs4 from bs330 Crank NBSU ST3 from bs430 Crank NBSU ST3 from bs445 Synchronize ST3 with bs445 Synchronize ST3 with bs4----------------------------------------------------------------------------------------------------------

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Sequence of Actions for Schuylkill-Southwark

============================================================Time (min.) ActionsTime (min.) Actions----------------------------------------------------------------------------------------------------------Restoration Building Block 2:Restoration Building Block 2:

0 Connect BSU CT30 Connect BSU CT3--4415 Energize bs9 from CT315 Energize bs9 from CT3--4420 Energize bs10 from bs920 Energize bs10 from bs925 Energize bs11 from bs1025 Energize bs11 from bs1030 Crank NBSU ST1 from bs1130 Crank NBSU ST1 from bs1145 Synchronize ST1 with bs1145 Synchronize ST1 with bs11

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Sequence of Actions for Schuylkill-Southwark

----------------------------------------------------------------------------------------------65 Energize bs1 from bs2, bs14 from bs2, bs12 from65 Energize bs1 from bs2, bs14 from bs2, bs12 from

bs3, bs5 from bs4, bs30 from bs9, bs8 from bs9, bs3, bs5 from bs4, bs30 from bs9, bs8 from bs9, bs17 from bs11, bs15 from bs11, bs25 from bs10bs17 from bs11, bs15 from bs11, bs25 from bs10

70 Energize bs22 from bs1, bs19 from bs14, bs13 from bs170 Energize bs22 from bs1, bs19 from bs14, bs13 from bs12, bs72, bs7from bs5, bs31 from bs39, bs21 from bs25, and synchfrom bs5, bs31 from bs39, bs21 from bs25, and synchronize ronize bs14 with bs15bs14 with bs15

75 Energize bs32 from bs31, bs20 from bs21, bs23 from bs75 Energize bs32 from bs31, bs20 from bs21, bs23 from bs22, 22, and connect bs7 with bs13, bs8 with bs7, and bs22 wand connect bs7 with bs13, bs8 with bs7, and bs22 with bs21ith bs21

80 Energize bs24 from bs23, bs26 from bs2080 Energize bs24 from bs23, bs26 from bs2085 Energize bs27 from bs2685 Energize bs27 from bs2690 Energize bs28 from bs2790 Energize bs28 from bs27----------------------------------------------------------------------------------------------------------

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Further Information

•• M. M. M. M. AdibiAdibi (Ed), (Ed), Power System Restoration Methodologies Power System Restoration Methodologies & Implementation Strategies& Implementation Strategies, IEEE Press, 2000., IEEE Press, 2000.

•• J. Wu, C. C. Liu, and R. Chu, J. Wu, C. C. Liu, and R. Chu, ““A Petri Net Algorithm for A Petri Net Algorithm for Scheduling of Generic Restoration Actions,Scheduling of Generic Restoration Actions,”” IEEE Trans. IEEE Trans. Power SystemsPower Systems, Feb. 1997, pp. 69, Feb. 1997, pp. 69--76.76.

•• L. Fink, K. L. L. Fink, K. L. LiouLiou, and C. C. Liu, , and C. C. Liu, ““From Generic From Generic Restoration Actions to Specific Restoration Strategies,Restoration Actions to Specific Restoration Strategies,””IEEE Trans. Power SystemsIEEE Trans. Power Systems, May 1995, pp. 745, May 1995, pp. 745--752.752.

•• K. L. K. L. LiouLiou, C. C. Liu, and R. Chu, , C. C. Liu, and R. Chu, ““Tie Line Utilization Tie Line Utilization during Power System Restoration,during Power System Restoration,”” IEEE Trans. Power IEEE Trans. Power SystemsSystems, Feb. 1995, pp. 192, Feb. 1995, pp. 192--199.199.

•• C. C. Liu, K. L. C. C. Liu, K. L. LiouLiou, et al., , et al., ““Generation Capability Generation Capability Dispatch for Bulk Power System Restoration Dispatch for Bulk Power System Restoration –– A A KnowledgeKnowledge--Based Approach,Based Approach,”” IEEE Trans. Power IEEE Trans. Power SystemsSystems, Feb. 1993, pp. 316, Feb. 1993, pp. 316--325. 325.