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“Cascading Events and How to Prevent Them”

“Cascading Events and How to Prevent Them”. The International Meeting of VLPGO WG#1 October 25, 2005. Background. Recurrent Cascading Outage Worldwide after Market Liberalization 1 st International Meeting of Very Large Power Grid Operators(VLPGO)

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“Cascading Events and How to Prevent Them”

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  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

  8. Scope of each WG WG-1 *Three WGs focused on technical issues excluding institutional issues, such as power market design.

  9. Issues associated with Cascading Events

  10. 2. Survey Results

  11. NG RTE ★ CAISO PJM ★ ★ ★ ★ GRTN ★ TEPCO Features of Very Large Power Grid

  12. System Configuration and Interconnection with Neighboring Systems [Maximum Short Circuit Current]

  13. Power Flow Level and Critical Stability Issues (Priority)

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

  15. Overview of Past Cascading Events <21th Century: After Market Liberalization>

  16. Common Causes of Recent Cascading Outages Deregulation of Electricity Market: Monopoly to Competition <Cause> Less Maintenance Priority to Market Mechanism Change of System Operation Rules Delay in Network Enhancement More Players More.. Complicated and Enlarged Power Grid Increase of Inter-regional (National) Power Exchange Fault Frequency Information to be Handled Uncertainty in Operating Condition <Impact> (To Interconnected Power System) (To Operators) Difficulty in Responding to Abnormal Situation Heavier Duty in Accommodating Electricity Transaction

  17. Mechanism of Cascading Outages-1 Trigger -Unexpected heavy loading -Unscheduled generation outage -Single fault (tree touching etc.) -Combination of above events • Impact of Market Liberalization • Cost Reduction • Wide-area Heavy Power Transaction Delay in Initial Action • Inappropriate On-line Monitoring • Need for Sophisticated On-line Monitoring System • Need for On-line Contingency Analysis Tool • Need for Automatic Preventive Control -Delay in grasping the situation -Delay in communication with neighboring operators -Delay in taking mitigation action

  18. Mechanism of Cascading Outages-2 Cascading Events: Alert to Emergency -Overloading -Voltage Collapse -Power Oscillation -Loss of Synchronism -Frequency Declining • Need for Enhancement of Emergency Control, so called ‘Safety Net,’ including ‘Islanding’ Protective Action -Transmission Lines -Transformers -Generators • Need for Time Coordination with Safety Nets, such as UFLS and UVLS

  19. Existing Countermeasures (Security Monitoring) <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 SEby using the PMU in combination with the 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

  20. Existing Countermeasures (Preventive Control) < 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 SecondaryVoltage 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”.

  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 restorationwhen designing the safety net.

  22. Future Countermeasures (Under Development) <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.

  23. Other Issues 1) Institutional Measures ◆Give TSO operators more authority ◆Establish a reliability standard applied to all relevant stakeholders ◆Contract among stakeholders who comply with the reliability standard ◆Establish strong coordination between TSOs in different time frames 2)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. Summary (Future R&D Topics) 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.

  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 questionnaire. 2. As a new and last aspect, add a “Restoration”. 3. Extend the survey area to the papers published by the PGOs with a capacity of less than 50GW.

  30. Thank you for your attention

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