1

“Cascading Eventsand

How to Prevent Them”

The International Meeting of VLPGO

WG#1

October 25, 2005

2

Background

Recurrent Cascading Outage Worldwide after Market Liberalization

1st International Meeting of Very Large Power Grid Operators(VLPGO)

- October 25-26, 2004, - Philadelphia, USA

- Objectives :

To find and share common concerns in “Maintaining Reliability”

To exchange good/bad experiences and the best existing practices

To cooperate on developing necessary measures

Set up three working groups

WG#1 :Cascading Events and How to Prevent Them (Lead: TEPCO)

WG#2 :EMS Architectures for 21th Century (Lead : PJM/MISO)

WG#3 :Advanced Decision Support Tools (Lead : RTE)

3

Objectives and Means

WG-1 surveyed the ways to prevent cascading events through a questionnaire to identify:

Common causes and mechanisms

Existing measures to be recommended

New technologies to be developed in the future

4

Contributors to WG#1

Mr.Hideaki TANAKA TEPCO JAPAN (Coordinator)Mr.Masanobu KAMINAGA TEPCO JAPAN

Mr.Michel KORMOS PJM USA

Dr.Yuri MAKAROV CAISO USA

Mr.Temistocle BAFFA SCIROCCO GRTN ITALY

Mr.Jean Michel TESSERON RTE FRANCE

Mr.Ian WELCH National Grid UK

5

Contents

1. Scope of Survey

2. Survey Results

3. Conclusion

6

1. Scope of Survey

7

Power System States and Transition

Security Monitoring

Preventive Control

Emergency Control

Normal

Restorative

In extremis

Restoration

Alert

Emergency

8

Scope of each WG

De-Centralized System

Centralized System

< In Control Centers >

Monitoring WG-3

*New technologies used by operators for decision making

WG-2

*Standardization of architecture platform for EMS

Control

*Three WGs focused on technical issues excluding institutional issues, such as power market design.

WG-1

9

Issues associated with Cascading Events

Power System

Stability

Thermal

Overloading

Rotor Angle

Stability

Small-Disturbance

Angle Stability

Transient

Stability

Frequency

Stability

Voltage

Stability

Large-

Disturbance

Voltage Stability

Small-

Disturbance

Voltage Stability

Cascading Blackouts

10

2. Survey Results

11

Features of Very Large Power Grid

NG

PJM★★★

★

★ RTE

★

TEPCO

CAISO

GRTN

Organization System

Capacity

[GW]

Highest

Voltage

[kV]

TEPCO 64 500

GRTN 54 380

National Grid 54 400

PJM 133 765

CAISO 48 500

RTE 83 400

12

System Configuration and Interconnection with Neighboring Systems

Organization

System Configuration

InterconnectionsEHV HV,MV

TEPCO Mesh

[ 63 kA]

Radial A 500kV AC link

Two BTBs

GRTN Mesh

[ 50 kA]

Radial Eight 380kV AC links

A 500kV DC link

A 200kV DC link

National Grid Mesh

[ 63 kA]

Radial AC Link

DC link

PJM Mesh

[ 63 kA]

Mesh 248 AC links

CAISO Mesh

[ 63 kA]

Mesh Five AC links

RTE Mesh

[ 63 kA]

Mesh 40 AC links

A 270kV DC link [Maximum Short Circuit Current]

13

Power Flow Level and Critical Stability Issues

Maximum Power Flow/ SIL

Critical Issues

Small-disturbance

Transient Frequency Voltage Thermal

Overloading

TEPCO

2.0

○

(1)

○

(2)

○

(3)

GRTN

1.5

○

(3)

○

(1)

○

(2)

National Grid

○ ○ ○

PJM ○ ○ ○

CAISO ○ ○ ○

RTE ○

(2)

○

(3)

○

(1)

(Priority)

14

Overview of Past Cascading Events <20th Century: Before Market Liberalization>

Date/Area

MW Lost, Duration

Causes(Trigger)

Critical Phenomenon

Nov. 1978/France

30,000MW 7 hr

- Major 400kV lines trips due to overloading

-Voltage collapse-System separation

Aug. 1981/UK

1,900MW 2.5 hr

- Loss of 3 400kV circuits and lower voltage interconnection

-System separation

Jan. 1987/France

8,000MW　　　　 3 hr

- Multiple generator trips -Voltage collapse

Jul. 1987/Tokyo

8,000MW 4 hr

- Insufficient VAR supply for high rate of load pickup

-Voltage collapse

Jul./Aug. 1996/Western US

11,850MW ? hr28,000MW 9 hr

- Loss of multiple lines and loss of critical generation

-Voltage collapse-System separation

-Power oscillation

15

Overview of Past Cascading Events <21th Century: After Market Liberalization>Date/Area

MW Lost, Duration

Causes (Trigger)

Critical phenomenon

Aug. 2003Northern US

61,800MW 42 hr

-Multiple line trips -Voltage collapse-System separation

Aug. 2003London

724MW 0.7 hr

-Incorrect operation of a backup relay

-Overloading

Sep. 2003Italy

20,000MW 20 hr

-Multiple EHV line trips -Voltage collapse (before system separation)

- Frequency collapse (after system separation)

-Power oscillation-System separation

Sep. 2003Scandia

6,550MW 6.5 hr

-Scrum of a Nuke plant-Double-bus fault

-Voltage collapse-Power oscillation

May. 2005Moscow

2,500MW 32 hr

-CT explosion-Multiple Tr explosion&fire

-Overloading

16

Common Causes of Recent Cascading Outages

Deregulation of Electricity Market: Monopoly to CompetitionDeregulation of Electricity Market: Monopoly to Competition

Priority to Market MechanismPriority to Market Mechanism

More PlayersMore Players

Less MaintenanceLess Maintenance

Delay in Network EnhancementDelay in Network Enhancement

Change of System Operation RulesChange of System Operation Rules

Increase of Inter-regional (National) Power ExchangeIncrease of Inter-regional (National) Power Exchange

Complicated and Enlarged Power GridComplicated and Enlarged Power Grid

Information to be Handled Information to be Handled

Uncertainty in Operating ConditionUncertainty in Operating Condition

Fault Frequency

Fault Frequency

Difficulty in Responding to Abnormal SituationDifficulty in Responding to Abnormal Situation

Heavier Duty in Accommodating Electricity Transaction Heavier Duty in Accommodating Electricity Transaction

<Cause>

More..

<Impact>(To Operators)

(To Interconnected Power System)

17

Mechanism of Cascading Outages-1

-Unexpected heavy loading

-Unscheduled generation outage

-Single fault (tree touching etc.)

-Combination of above events

-Delay in grasping the situation

-Delay in communication with neighboring operators

-Delay in taking mitigation action

Trigger

Delay in Initial Action

Impact of Market Liberalization

Cost Reduction

Wide-area Heavy Power Transaction

Inappropriate On-line Monitoring

Need for Sophisticated On-line Monitoring System

Need for On-line Contingency Analysis Tool

Need for Automatic Preventive Control

18

Mechanism of Cascading Outages-2

-Transmission Lines

-Transformers

-Generators

Protective Action

Need for Time Coordination with Safety Nets, such as UFLS and UVLS

-Overloading

-Voltage Collapse

-Power Oscillation

-Loss of Synchronism

-Frequency Declining

Cascading Events: Alert to Emergency

Need for Enhancement of Emergency Control, so called ‘Safety Net,’ including ‘Islanding’

19

<Findings>1) On-line state estimator(SE) is commonly used

*Maximum Capacity: 7400 nodes, 2500 generators, every one minute

2)On-line contingency analysis is also commonly implemented, both for ‘voltage instability’ and ‘thermal overloading’

3) On-line direct monitoring of power system oscillation has started in some countries. In the US and EU, GPS-based PMU (Phasor Measurement Unit) is applied to monitor the phase.

<Challenges>1) To improve the accuracy of SE by using the PMU in combination with th

e conventional SE

2) To extend the scope of contingency evaluation into phase angle stability, in particular transient stability

3) To estimate the frequency/power regulation performance of the system

Existing Countermeasures (Security Monitoring)

20

< Findings>1) Power System Stabilizer is a common tool to prevent small-signal

instability.2) High-speed re-closing including multi-pole re-closing is adopted in order

to improve transient stability, while aiming to put the network back to its initial state.

3) Automatic Generator Control is commonly used to maintain system frequency.

4) A wide variety of de-centralized automatic control systems are used to prevent the transition to the alert state, as well as to lighten operators’ burden.

5) In France, a centralized automatic control system called the Secondary Voltage Control System, has been in operation at the regional level, the purpose of which is to get better control performance.

<Challenges>1) To select a centralized system or de-centralized system appropriately in

accordance with system features 2) To develop a sophisticated algorithm that can provide the operators with

information on how to prevent the transition from “Alert” to “Emergency”.

Existing Countermeasures (Preventive Control)

21

Existing Countermeasures(Emergency Control)

< Findings>1) Several types of ‘emergency controls’ have been developed as a

‘safety net’ and are in operation.

They are categorized into the following three categories:<Generator Tripping>

OFLS, SPS (Generators, Pumped-Storage Units etc.)<Load Shedding>

UFLS, UVLS, SPS (Loads), [Blocking of Tap Changers]<System Separation>

Islanding

<Challenges>1) To keep the interconnection as long as possible, even when an

emergency occurs, ‘Time coordination’ between the equipment protection system and emergency control systems must be examined.

2) To consider quicker restoration when designing the safety net.

22

<Findings>

1) The following systems, mainly for “Monitoring “, are now under development. On-line transient stability assessment in the US and Japan PMU-based small-signal stability monitoring system in the US. A wide area monitoring system, which covers all issues regarding

cascading events and includes the centralized voltage control system in Italy.

Monitoring of Generator performance and of f/P power system performance in France.

2)Currently, no emergency control system is being developed.

Future Countermeasures (Under Development)

23

Other Issues

1) Institutional Measures ◆Give TSO operators more authority ◆Establish a reliability standard applied to all relevant stakeh

olders ◆Contract among stakeholders who comply with the reliability

standard ◆Establish strong coordination between TSOs in different tim

e frames2)Other Measures ◆ Aim Operator Training Simulator at:

Improving the knowledge and skills of the individuals

Developing the operator’s tolerance for psychological stress and capability of coping with abnormal conditions

◆Risk indices used to set adequate reserve margins or to allow operators know the necessity of load shedding

24

3. Conclusion

25

Summary (Existing Measures)

1)There were several types of automatic centralized/de-centralized systems for “Monitoring”, “Preventive Control”and “Emergency Control”, respectively.

<centralized> <decentralized> Monitoring : ◎ Preventive Control : ○ ○ Emergency Control : ◎ 2) Each VLPGO will be able to select and employ the

most appropriate systems from the “Seasoned Best Practice Menu”.

26

1)Since the use of “Emergency control ” is a last resort measure, we should focus future R&D mainly on “Monitoring ” and “Preventive Control ”, which are tools used “upstream” of cascading events.

2)Upon reviewing survey results, we have identified the following R&D topics to be further addressed.

Summary (Future R&D Topics)

27

< Reinforcement of Monitoring> On-line Dynamic Assessment (PJM,TEPCO) - On-line High Speed Screening On-line System stability(Steady state/Dynamic)

Monitoring (CAISO) - PMU application - Eigenvalue calculation Wide Area Measurement (GRTN) Generator and System f/P Performance

Monitoring(RTE)

<Reinforcement of Preventive Control> On-line Corrective Action(switching or re-dispatching)

Indicating System (RTE)

28

3) In the process of R&D, we should take into account : Up-to-date IT technologies Parallel computing techniques Advanced algorithms for on-line analyses Standardization of software and

architecture.

29

Recommendation on 2006 action plan

<Mission>Develop a “Comprehensive Survey Paper” on the ways to prevent cascading blackouts by the next VLPGO meeting for presentation at an International Conference such as CIGRE

<Action>1. Recruit new members and dispatch questionn

aire.2. As a new and last aspect, add a “Restoratio

n”. 3. Extend the survey area to the papers publish

ed by the PGOs with a capacity of less than 50GW.

30

Thank you for your attentionThank you for your attention