1

Panel Session at IEEE PES GM 2015

Microgrids in Distrib tion S stem RestorationDistribution System Restoration

Chen‐Ching LiuBoeing Distinguished Professor Washington State University

(Also Professor, University College Dublin)

Research Sponsored by PNNL and Dept of Energy

SGIGs on Distribution Automation SGIGs on Distribution Automation 

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• Deployment of technologies and systems for improving distribution system operations, including: (1) outage management with devices such as automated circuit switches and reclosers, and (2) voltage/volt‐ampere reactive (VAR) control with field devices such as automated capacitors, voltage regulators, and voltage sensors.

Installed SGIG Automated SwitchesInstalled SGIG Automated Switches

Example:

Avista Utilities WAAvista Utilities, WA

Spokane and Pullman

(WSU) Smart Circuit

Installed SGIG Automated Capacitors

(WSU) Smart Circuit

Project Cost: $40MProject Cost: $40M

Fed Funding: $20M

Source: http://energy.gov/sites/prod/files/Smart%20Grid%20Investment%20Grant%20Program%20-%20Progress%20Report%20July%202012.pdf

Fed Funding: $20M

Reliability ImprovementsReliability Improvements3

• 48 SGIGs are applying DA technologies to improve reliability:• 42 deploying automated feeder switches (1 to > 1000’s of switches)p y g ( )

– Enables fault location, isolation and service restoration functions 

• System integration schemes (AMI/OMS/DMS/SCADA/GIS)– 26 projects are applying distribution management systems– 36 implementing AMI outage notification– 22 deploying equipment health sensors

I i i l l f 4 P j (1 250 f d ) A il 1 2011 h h M h 31 2012• Initial results from 4 Projects (1,250 feeders) ‐ April 1, 2011 through March 31, 2012

Source: http://tcipg.org/sites/tcipg.org/files/slides/2013_02-01_Arnold.pdf

Distribution System Restoration (DSR)4

Distribution System Restoration (DSR)• A smart grid application and an important objective of 

distribution automation.• Restore critical load during extreme events.• A typical multi‐objective, combinatorial problem with  

constraints, including topological and electrical constraints.

Restore loads in a secure and efficient manner

Selecting and sequencing a set of switching

operationsReduce the duration of outages and improve

reliability

Distribution System

Restoration

reliability

Service Restoration with DA (1)*5

Service Restoration with DA (1)1. Fault occurs 2. Open CB

3. Find fault 4. Isolation

Korean Electric Power Company: Intelligent DA System

Service Restoration with DA (2)*6

Service Restoration with DA (2)5. Transfer outage area 6. Execute restoration plan

7 Field crew7. Field crew

KEPCO: Intelligent DA System

Basic DSR Strategies*7

Basic DSR StrategiesSingle Double Tripleg p

Single & level‐2 Double & level‐2 Selfg

KEPCO: Intelligent DA System

Problem Formulation

A constrained multi-objective problem

Objectives: - (minimize the total number of switch operations)

( i i th t f t t l l d t d)- (maximize the amount of total load restored)

Subject to following constraints:

, Line Capacity Constraint ,

Node Voltage Constraint, Node Voltage Constraint ,

, Transformer Capacity Constraint,

A radial network structure is maintained,

8

,

Unbalanced three phase power flow is satisfied.

9

J. Li, X. Y. Ma, C. C. Liu, K. Schneider, “Distribution System Restoration with Microgrigd Using Spanning Tree Search,” IEEE Trans Power Systems Nov 2014 pp 3021 3029

Distribution Network Topology and Spanning TreeIEEE Trans. Power Systems, Nov. 2014, pp. 3021-3029

Radial structure of the distribution network can be represented by a spanning tree.

Restoration can be formulated as a problem of finding a desired spanning tree structure and a sequence of operations that change one spanning tree into anotherspanning tree into another.

Spanning Tree Representation for Distribution Feeders

J. Li, X. Y. Ma, C. C. Liu, K. Schneider, “Distribution System Restoration with Microgrigd Using Spanning Tree Search,” IEEE Trans. Power Systems, Nov. 2014, pp. 3021-3029.

Proposed Distribution System Restoration AlgorithmEach Class of Spanning Trees Candidate TopologiesEach Class of Spanning Trees Candidate Topologies

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Microgrids Enhance Restoration Capability

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Microgrids Enhance Restoration Capability

• Generation resources and control capabilities of• Generation resources and control capabilities of microgrids enhance fast recovery of distribution systems.

• Grid connected mode and• Grid‐connected mode andisolated mode.

• When a blackout occurs, microgrids can be controlled

d ffMicrogrid

to provide an efficient DSR strategy to reduce the 

f hrestoration time of the distribution system.

Restoration schemes considering DERs and Microgrids

Integrate Microgrids into DSR Algorithm12

Integrate Microgrids into DSR Algorithm

• Microgrids are modeled as virtual feeders• Generation limits of DERs are formulated as electrical constraints of the distribution feeders.

• The island configuration Microgrid Virtual FeederThe island configuration of the microgrid can be modeled as a supplemental 

F2 F3

1 26

7 8 9 14 15 16 17 18

13 19

Microgrid Virtual Feeder

ode ed as a supp e e atopology constraint of the distribution system. F5

F41 2

4

512

11 10

2021

23

22

yF1 3 11 10

Load NodeClosed Switch

(branch)Open Switch

(branch)

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Example – Microgrid Supports Fast

• One line diagram of Pullman WSU System

Example  Microgrid Supports Fast Recovery of Distribution Systems

• One‐line diagram of Pullman‐WSU System

1

13

(Root)

SPU121 48 34 37

29

35

41

30

32 21 2322 24 27

414

7 12

SPU12249

39

43 15 16

City Hall & Police Station

G3 2 1 MW

3

5

9

SPU123

SPU124

50

171840

3831

36 42Hospital

G3

G2 1.1 MW

2.1 MW

26 8 10

SPU12451 20 19

G1 1.1 MW

11 SPU125 52 46 45 33 44 47 28 25 26

WSU MicrogridSPU Substation

Load Sections Normally Closed Switch Normally Open SwitchLoad Sections Normally Closed Switch Normally Open Switch

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Example – Microgrid Supports FastExample  Microgrid Supports Fast Recovery of Distribution Systems (Conti.)

• Scenario Description– A severe event happened in the South Pullman 115kV– A severe event happened in the South Pullman 115kV Substation.

– As a result all 5 feeders served by the substation are outAs a result, all 5 feeders served by the substation are out of service.

• Feeders: SPU121, SPU122, SPU123, SPU124, SPU125• Critical loads: Hospital, City Hall, Courthouse and Police Station

– No source in the Avista system can be used for restoration.– WSU generators will be used to restore critical loads.

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Example – Microgrid Supports FastExample  Microgrid Supports Fast Recovery of Distribution Systems (Conti.)

• Spanning Tree Search algorithm is applied to find the restoration paths from DERs to critical loads.

Critical Load13SPU121

48 34 37

29

35

41

30

32 21 2322 24 27

14SPU122

49

39

43 15 16

1718

City Hall & Police Station

G3 2.1 MW

Critical Load10

9SPU123

SPU12451

50

184038

31

36 42

20 19

Hospital

G1

G2

1.1 MW

1.1 MW

Source11

SPU12552 46 45 33 44 47 28 25 26

WSU Microgrid

Example – Microgrid Supports Fast16

Example  Microgrid Supports Fast Recovery of Distribution Systems (Conti.)

• Restoration Path: G3 17 19 20 34 37 41 32 39 42 36 38 40

13SPU121

48 34 37

29

35

41

30

32 21 2322 24 27City Hall

City Hall, Courthouse, Police Station Hospital

14SPU122

49

39

43 15 16

171840 31

City Hall, Courthouse

& Police Station

G3 2.1 MW

G3, a diesel generator, is used to pick up critical loads i e City Hall

10

9SPU123

SPU12451

50

038

31

36 42

20 19

Hospital

G1

G2

1.1 MW

1.1 MW loads, i.e., City Hall, Courthouse, Police Station and Hospital.

11SPU125

52 46 45 33 44 47 28 25 26

WSU Microgrid

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Example – Microgrid Supports FastExample  Microgrid Supports Fast Recovery of Distribution Systems (Conti.)

• Validation by GridLAB‐D Power FlowG3 17 19 20 34 37 41 32 39 42 36 38 40

City Hall, Courthouse, Police Station Hospital

PNNL Test SystemWith Microgrids18

PNNL Test System With MicrogridsZ31 Z35

Z29

Z17 Z20

Z25

Z28

Z39

Microgrid 1

Z38 Z3

Z33

Z12

Z40

Z13

Z15

M

F-a Z1 Z24 Z22 Z4 Z30 Z18 Z23 Z6 Z7 Z19 Z2 Z14 Z16 Z9 Z26 Z27

Z34 Z21

Z37

Z31

Z8

Z36

Z35

Z5

Z32

Z17 Z20 Z39 Z38

Z10

Z3

Z11

Z12 Z13

Microgrid 2T2Z68 Z55 M

FB-a

F-b Z41 Z64 Z62 Z44 Z70 Z58 Z63 Z46 Z47 Z59 Z42 Z54 Z56 Z49 Z66 Z67

Z71

Z48

Z75

Z45

Z69

Z57 Z60

Z65

Z79 Z78

Z50

Z43

Z73

Z52

Z80T1

T3FB-b

Z74 Z61

Z77

Z76 Z72 Z51 Z53

F Z94 Z106 Z107

Z111

Z88

Z116Z115

Z85

Z109

Z97 Z100

Z105

Z119 Z118

Z90

Z83

Z113

Z93

Microgrid 3

T3

T7

T6

Sub-Transmission

Z108 Z95

MS

F-c Z81 Z104 Z102 Z84 Z110 Z98 Z103 Z86 Z87 Z99 Z82 Z94 Z96 Z89 Z106 Z107

Z114 Z101

Z117

Z85

Z112

Z90

Z91Z92

Z120

Z149 Z145 Z153

T4T5

Node

Z148 Z135

FB-c

F-d Z121 Z144 Z142 Z124 Z150 Z138 Z143 Z126 Z127 Z139 Z122 Z134 Z136 Z129 Z146 Z147

Z154 Z141

Z151

Z128

Z155

Z156

Z125

Z152

Z137 Z140 Z159 Z158

Z130

Z123

Z131Z132Z160

Z133Microgrid 4

M

FB-d

Z157

Voltage Regulator Tie/Microgrid SwitchF-a Feeder Id Sectionalizing Switch M MicrogridLoad Zone Feeder Breaker

Example19

Example• A fault occurs at zone Z43A fault occurs at zone Z43

F-a Z1 Z24 Z22 Z4 Z30 Z18 Z23 Z6 Z7 Z19 Z2 Z14 Z16 Z9 Z26 Z27

Z31

Z8

Z35

Z5

Z29

Z17 Z20

Z25

Z28

Z39

Microgrid 1

Z38

Z10

Z3

Z33

Z12

Z40

Z13

Z15

M

FB

Z34 Z21

Z37

Z36 Z32 Z11

F b

Z71 Z75

Z69

Z57 Z60

Z65

Z79 Z78

Z50

Z43

Z73

Z52

Z80

Microgrid 2

T1

T2Z68 Z55 M

FB-a

Restoration Scheme•Close: 73-Microgrid 2F-b Z41 Z64 Z62 Z44 Z70 Z58 Z63 Z46 Z47 Z59 Z42 Z54 Z56 Z49 Z66 Z67

Z74 Z61

Z77

Z48

Z76

Z45

Z72

Z50

Z51 Z53

Z111 Z116Z115

Z109

Z97 Z100

Z105

Z119 Z118 Z83

Z113

Z93

Microgrid 3

T3

T7

T6

Sub-

Z108 Z95

MS

FB-b

Close: 73 Microgrid 2

• Without Microgrid 2F-c Z81 Z104 Z102 Z84 Z110 Z98 Z103 Z86 Z87 Z99 Z82 Z94 Z96 Z89 Z106 Z107

Z114 Z101

Z117

Z111

Z88

Z115

Z85

Z112

Z97 Z100 Z119 Z118

Z90

Z83

Z91Z92

Z120

Z93

Z149 Z145 Z153

T4T5

Sub-Transmission

Node

Z148 Z135

FB-c

• Without Microgrid 2,zone Z73 cannot berestored!

F-d Z121 Z144 Z142 Z124 Z150 Z138 Z143 Z126 Z127 Z139 Z122 Z134 Z136 Z129 Z146 Z147

Z154 Z141

Z157

Z151

Z128

Z155

Z156

Z125

Z152

Z137 Z140 Z159 Z158

Z130

Z123

Z131Z132Z160

Z133Microgrid 4

M

FB-d

Voltage Regulator Tie/Microgrid SwitchF-a Feeder Id Sectionalizing Switch M MicrogridLoad Zone Feeder Breaker

Restoration with/without Microgrids20

Restoration with/without Microgrids• Microgrid Enhance Restoration CapabilityMicrogrid Enhance Restoration Capability

– Using the capability of microgrids to pick up more interrupted load (Scenario 1 & 2)( )

– Microgrids reduce the number of switching operations during restoration (Scenario 3) 

Scenario # Fault Location Switching Operations without Microgrids Switching Operations with Microgrids

1 Zone Z43 ‐‐‐ Close: 73‐Microgrid2

2 Zone Z139

Open: 46‐47, 96‐89Close: 136‐120, 53‐96, 45‐90

Partial Restoration, 315.04 kVA load should be shed at F‐b

Open:50‐43, 90‐92Close: 45‐90, 73‐Microgrid2,

136‐120

3 Zone Z23Open: 49‐50, 90‐92

Close: 78‐9, 53‐96, 136‐120Close: 39‐Microgrid1

Improvement in Reliability21

Improvement in Reliability

• SAIDI, SAIFI and Outage Cost are calculated. *Index Without Microgrids With Microgrids ImprovementIndex Without Microgrids With Microgrids Improvement

SAIDI(minute/year) 196.54 182.64 7.07%

SAIFI (/year) 0.7800 0.7800 0 % **

Outage Cost 3729 8 3426 5 8 13%g(k$/year) 3729.8 3426.5 8.13%

* Assume that the permanent failure rate for each zone is 0.02, the mean ti t t ( l) it h i 90 i t d th t f ttime to operate a (manual) switch is 90 minutes, and the cost for outage load is $1 per kW per minute, respectively.** In order to improve SAIFI, remote-controlled ability should be added.

Differences Between Typical Outages and

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Differences Between Typical Outages and Catastrophic Outages Due to Extreme Events

Typical Outages Catastrophic Outages

• Single fault: In most cases, there is only f l d

• Multiple faults: Multiple electrical f ili i d done faulted component.

• Small amount of load and a small number of customers are involved.

facilities are damaged.

• Large amount of load and a large number of customers are out of

• Power is available: Most power so rces are orking and sta connected

services.

• Lack of power: Power sources can not access the load or are o t of ser icesources are working and stay connected.

• T&D network remains intact: Outage loads are easily connected to sources.

access the load or are out of service.

• T&D network damaged: Overhead lines, transformers, substations are

• Easy to repair and restore

damaged.

• Difficult to repair and restore

Further InformationFurther InformationY X C C Li H G ”R li bili A l i f Di ib i S C id i S i• Y. Xu, C. C. Liu, H. Gao,”Reliability Analysis of Distribution Systems Considering Service Restoration,” IEEE PES ISGT, Feb. 2015.

• J. Li, X. Y. Ma, C. C. Liu, K. Schneider, “Distribution System Restoration with Microgrigd Using Spanning Tree Search “ IEEE Trans Power Systems Nov 2014 pp 3021‐3029Using Spanning Tree Search,   IEEE Trans. Power Systems, Nov. 2014, pp. 3021‐3029.

• S. I. Lim, S. J. Lee, M. S. Choi, D. J. Lim, and B. N. Ha, “Service Restoration Methodology for Multiple Fault Case in Distribution Systems,” IEEE Trans. Power Systems, Nov. 2006.

• S. J. Lee, S. I. Lim, B. S. Ann, “Service Restoration of Primary Distribution Systems Based onS. J. Lee, S. I. Lim, B. S. Ann,  Service Restoration of Primary Distribution Systems Based on Fuzzy Evaluation of Multi‐Criteria,” IEEE Trans. Power Systems, Aug. 1998, pp. 1156‐1163.

• M. S. Tsai, C. C. Liu, V. N. Mesa and R. Hartwell, "IOPADS (Intelligent Operational Planning Aid for Distribution Systems)," IEEE Trans. Power Delivery, July 1993, pp. 1562‐1569. 

• C. C. Liu, S. J. Lee and K. Vu, "Loss Minimization of Distribution Feeders: Optimality and Algorithms" IEEE Trans. Power Delivery,  April 1989, pp. 1281‐1289. 

• C.C. Liu, S.J. Lee, S.S. Venkata, “An Expert System Operational Aid for Restoration and Loss Reduction of Distribution Systems” IEEE Trans. Power Systems, May 1988, pp. 619‐626.