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September 2011 Pacific Southwest Disturbance

September 2011 Pacific Southwest Disturbance. Presented by George V. Noller John Page. Course Objectives. By the end of this session, you should be able to: Describe the primary cause of the September 8 2011 Southwest Blackout as stated in the NERC report .

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September 2011 Pacific Southwest Disturbance

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  1. September 2011Pacific SouthwestDisturbance Presented by George V. Noller John Page

  2. Course Objectives • By the end of this session, you should be able to: • Describe the primary cause of the September 8 2011 Southwest Blackout as stated in the NERC report. • List applicable NERC Reliability Standards that were referenced in the report on the September 8 2011 event • Sequentially list the major events of the disturbance • Give a brief description of the restoration process used after the blackout

  3. Goal • Review the findings of the NERC report regarding the September 8 2011 Southwest Outage • This is not intended to critique operator actions

  4. Report http://www.nerc.com/page.php?cid=5|407

  5. NERC Standards • COM-002-2, R2 • Issue directives in a clear and concise manner • Three-part communication • EOP-001-2.1b • Developing, maintaining and implementing emergency plans • EOP-003-2 • Shed load rather than risking uncontrolled failure or cascade • EOP-005-2 • Returning system to normal following a disturbance • EOP-006-2 • Coordination with Reliability Coordinator • TOP-004-2 • Operate so that instability, uncontrolled separation, or cascading outages will not occur as a result of the most severe single contingency

  6. Synopsis • A regional disturbance occurred on the afternoon of September 8, 2011 which led to cascading outages and loss of load • SDG&E, IID and CFE had complete system outages • APS and WALC had customers interrupted in the lower Colorado River area

  7. Synopsis • This disturbance occurred on a heavily loaded summer day • Load interrupted: • SDG&E 4293 MW • CFE 2150 MW • IID 929 MW • APS 389 MW • WALC 74 MW

  8. Synopsis • Report findings: The system was not being operated in a secure state for an N-1 outage due to: • Lack of information sharing between entities • Lack of adequate studies • Sub -100 kV facilities not adequately considered in next-day studies • Initiating event: Loss of APS Hassayampa-North Gila 500 kV Line due to an operating error • All load was restored in approximately 12 hours • Restoration proceeded rather smoothly

  9. State of the System • A very warm day in the Pacific Southwest with typical high system loads and heavy east-to-west transfers into Southern California • Paths leading into the disturbance area were loaded at greater than 50% of path ratings with the highest path at 78% • SDG&E imports were at 89% of limit

  10. State of the System

  11. 57 MW 1620 MW 70 MW 1285 MW 1391 MW

  12. Sequence of Events – Event 1 • At 1527, APS Hassayampa-North Gila 500 kV Line relayed • APS technician was conducting switching to externally bypass the line series capacitor at North Gila Substation • The technician performed the switching out of sequence and opened the capacitor line disconnect prior to closing the bypass disconnect • This action caused the disconnect to flashover (phase to phase) as it was incapable of interrupting load current

  13. Sequence of Events – Event 1 • The loss of this 500 kV line caused the underbuilt 230, 161 and 92 kV systems in the area to load up • At IID’s Coachella Valley Substation, the No.1 and No.2 Banks 230/92 kV exceeded their normal ratings by just over 25%, which was within the minimum trip for the bank overcurrent relays • CFE lost 156 MW of generation in the Mexicali area and requested assistance from CAISO, which was provided • APS told WECC RC that they would be placing the line back in service momentarily • Post-disturbance studies showed that the phase angle difference would have been too high for a successful synchronization

  14. Sequence of Events – Event 2 • 15:28:16 IID Coachella Valley No.1 and No.2 Banks 230/92 kV relayed on overcurrent . • This caused an extreme overload on IID Ramon Sub No.1 Bank 230/92 kV – greater than 207% of full load rating (225 MVA) • Severe voltage depression occurred in the WALC 161 kV system near Blythe Substation as the flows from Arizona tried to find ways into the SDGE/IID/CFE area

  15. Sequence of Events – Event 2 • Path 44 (South of SONGS) increased to 6600 amperes following this event. The intertie overcurrent relays were set at 8000 amperes • Low voltages were observed throughout Southern California and the Colorado River Valley • Manual and automated capacitor switching commenced

  16. 105 MW +48 2030 MW +410 150 MW +80 2407 MW +1122 North Gila-Imperial Valley 500 kV line flow reverses to feed Yuma Area Load. 60 MW CFE Unit 160 MW

  17. Sequence of Events – Event 3 • 15:32:10: Less than five minutes after the trip of H-NG, Ramon Sub No.1 Bank 230/92 kV relayed on overcurrent • IID northern transmission system entered a voltage collapse condition, with 92 kV voltages at 45% of normal momentarily • IID UVLS operated as well as 161 kV and 92 kV lines relaying, causing a loss of nearly 50% of IID’s load • WALC’s 161 kV system south of Blythe continued to overload and voltages continued to drop

  18. Sequence of Events – Event 3 • CAISO initiated unit starts through exceptional dispatch • APS continued steps to return the 500 kV line to service • South of SONGS flows increased to 7800 amperes momentarily and settled out at 7200 amperes • Voltages continued to decline in the area

  19. 105 MW 2120 MW +90 IID Lost 400 MW 2607 MW +200 1532: IID Blythe-Niland and Coachella Valley- Niland 161 kV Lines Relay and Ramon 230/92 Banks Relay 60 MW CFE Unit 160 MW

  20. Sequence of Events – Event 4 • 15:35 APS Yuma load pocket separates from the WALC/IID161 kV system when WALC Gila Sub No.1 and 2 Banks 161/69 kV, APS Yucca Sub No.1 and No.2 Banks 161/69 kV and IID Pilot Knob No.1 and 2 Banks 161/92 kV relayed on overcurrent • Cogeneration in the Yuma area relayed while carrying 52 MW • APS load was now radially fed from the SDG&E system through Imperial Valley to North Gila • South of SONGS loading increased to 7800 amperes

  21. Sequence of Events – Event 4 • CAISO increased the amount of exceptional dispatch in an attempt to reduce South of SONGS loading. Speed limited by existing technology • The additional units requested had a 10 minute start time • WALC ordered MWD to shed 80 MW pump load to assist with voltage recovery in the Parker Dam area

  22. Sequence of Events – Event 5 • For approximately 25 seconds, a high speed cascade occurs, which separates SDG&E, IID, CFE and portions of APS and WALC from the interconnection • IID El Centro-Pilot Knob 161 kV Line relays on zone 3 distance protection • SCE Blythe Energy RAS operated, tripping 128 MW of generation • IID ‘S’ Line RAS operated, opening Imperial Valley-El Centro 230 kV Line ‘S’ separating IID from the interconnection

  23. 105 MW 2120 MW IID No. System 2890 MW +283 1537: IID RAS Trips La Rosita Units and relays IV-El Centro 230 kV Line. IID Southern System Blacked out. IID So. System 330 MW +212 La Rosita 420 MW APS Unit 51 MW CFE Unit 160 MW

  24. 105 MW 2120 MW IID No. System 2890 MW +283 1534: IID and APS Units Relay 1537: WALC & IID Separate at Pilot Knob IID Unit 44 MW 118 MW +58 APS Unit 51 MW CFE Unit 160 MW

  25. Sequence of Events – Event 6 • South of SONGS flows increased to 9500 amperes momentarily and dropped to 8700 amperes, above the minimum trip setting of 8000 amperes • Approximately 20 seconds later, the SONGS System Separation Scheme operated, separating SDG&E, CFE and portions of APS & WALC from the interconnection • There were no alarms at SDG&E, SCE or CAISO that indicated the flows were above minimum trip

  26. Sequence of Events – Event 7 • 15:38 After separation, the islanded area frequency decayed rapidly • UFLS occurred throughout the island, but subsequent generator trips prevented the island from balancing • UF relays also operated to separate SDG&E, CFE and APS from each other • At approximately 7 seconds after separation, the islands collapsed • Within several seconds of separation, both San Onofre units relayed when rapid acceleration occurred momentarily (due to change in the impedance of the system) and reactor protection operated • 11 minutes from loss of 500 kV Line to collapse

  27. 1538: San Onofre System Separation initiates on overload and Units 2 and 3 subsequently trip during disturbance. IID No. System 400 MW SDGE System 4300 MW IID So. System 550 MW IID Unit APS Yuma Area 390 MW CFE System 2200 MW

  28. Restoration • According to the NERC report, none of the affected entities utilized their black start plans due to availability of ties with neighboring utilities • South of SONGS and Hassayampa – North Gila • Outside in restoration • Once started, restoration proceeded rather smoothly

  29. Restoration • Delays were encountered at San Onofre in resetting the intertie overcurrent lockout relay due to plant conditions not meeting the requirements to reset • This delay caused the dispatcher at SCE to order the operator at San Onofre to reset the relay

  30. Restoration • After resetting the lockout relay, restoration in the SDG&E system commenced • The Hassayampa-North Gila 500 kV Line was restored to service and provided SDG&E with two sources for restoration – one from SCE and the other from APS

  31. Restoration • The two sides of the system were synchronized at 2258, seven hours and 20 minutes after the collapse • This was delayed due to discussions occurring between the CAISO and the TOPs regarding closing angle limitations.

  32. Restoration • IID system load restored at 2140 • CFE system load restored at 0137 9/9/11 • SDGE system load restored at 0323 9/9/11

  33. Restoration

  34. Restoration • Challenges encountered during the restoration • Communication with San Onofre operators • Voltage control with lightly loaded lines and San Onofre units off • Phase angle difference between CA and AZ with no prior guidelines on limits • Maintaining adequate limits on paths • Having resources available for rapid restoration

  35. Restoration • Items that worked well • Communication between CAISO and TOPs went relatively smooth – Possibly due to CETAC? • Coordination between SCE and SDG&E went very well due to annual regional drills. • System performed as expected

  36. Discussion • Are there any sub-100 kV areas in your system that could affect the reliability of the BES? • SCE 66 kV system in Antelope area • SCE 55 kV system to Nevada • SDG&E 69 kV underbuilt • PGAE 60/70 kV underbuilt • CFE 69 kV underbuilt

  37. Report Findings Some of the findings of the report: • Failure to Conduct and Share Next-Day Studies • Sub-100 kV Facilities Not Adequately Considered in Next-Day Studies • Lack of Real-Time External Visibility

  38. Report Findings • Inadequate Real-Time Tools • Reliance on Post-Contingency Mitigation Plans • WECC RC Staffing Concerns • WECC RC and affected TOPs and BAs do not consistently recognize the adverse impact sub-100 kV facilities can have on BPS reliability • Lack of Review and Studies on Impact of SPSs Some of the findings of the report:

  39. Epilogue • NERC/FERC took over the analysis of the disturbance and issued their report without input from the entities affected • The report only covers the causes of the disturbance and their recommendations • Any possible violations of NERC standards and any potential sanctions are still being investigated

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