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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 2011Pacific SouthwestDisturbance 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. • 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
Goal • Review the findings of the NERC report regarding the September 8 2011 Southwest Outage • This is not intended to critique operator actions
Report http://www.nerc.com/page.php?cid=5|407
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
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
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
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
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
57 MW 1620 MW 70 MW 1285 MW 1391 MW
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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.
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
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
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
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
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
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:
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