2011 Southwest blackout

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States with areas largely affected by the Southwest Blackout of 2011

The 2011 Southwest blackout, sometimes referred to as the Great Blackout of 2011,[1][2] was a widespread power outage that affected large areas of Southern California as well as western Arizona and northern Baja California and Sonora.[3] It occurred on Thursday, September 8, 2011, beginning at about 3:38 pm PDT. It was the largest power failure in California history.[4]


a map

SDG&E's system is connected to Arizona by the Southwest Power Link, which is a single 500 kV power line (afterwards, SDG&E built a second line, but this connects in the Imperial Valley and the Arizona section is still a single line). There is no connection at the 500 kV level between SDG&E and SCE (or LADWP). Rather, they are both connected to "SONGS" (San Onofre Nuclear Generating Station). IID has a 92 kV system connected to both.


Five utilities were affected: San Diego Gas & Electric, a subsidiary of Sempra Energy that serves San Diego County and parts of southern Orange County and parts of Riverside County; the Imperial Irrigation District, serving the Imperial Valley; the portion of Comisión Federal de Electricidad, Mexico's electric utility, serving Baja California; Arizona Public Service; and Western Area Power Administration - Lower Colorado. The blackout left nearly seven million people without power,[3] including 1.4 million customers in San Diego County[5][6] and 1.1 million customers in Mexico.[3] The outage was the result of 23 distinct events that occurred on 5 separate power grids in a span of 11 minutes.[7] Federal, regional and local officials are investigating what happened and why the outage cascaded the way it did.[8] The Arizona Public Service (APS) North Gila Substation reported power loss at 3:27 pm PDT. Within seconds a portion of a Mexico power plant shut down, but there is no indication that Arizona impacted Mexico.[7] Units 2 and 3 at San Onofre Nuclear Generating Station automatically tripped offline due to a "grid disturbance" which initiated the plant's Emergency Feed Actuation System (EFAS).[9]

The hardest hit region of the blackout, the San Diego-Tijuana metropolitan area, was essentially brought to a standstill. Surface streets became gridlocked due to the loss of traffic signals, and the San Diego skyline went dark. The San Diego Trolley system was shut down as there was no power to operate signal lights and related functions, and trains were stopped in Los Angeles for the same reason. Citizens in Tijuana and in inland areas like the Coachella Valley stayed outdoors late into the night to escape the heat.[6] Freeways in the Southern California megalopolis experienced extreme clogging, especially on the I-15 and I-5 corridors between southwestern Greater Los Angeles and the San Diego area's North County.[6] One hospital was left without power for two hours when its backup generator failed.[10] Only a few areas in the region, such as Blythe, California in the Palo Verde Valley, were not affected by the outage.[11]


Eleven hours after the outage began, power was restored to 694,000 of the affected customers,[12] and by 4:30 am on September 9 power was restored to all customers, although the system was described as "still fragile".[13] As a precaution, all public schools in San Diego County and the Capistrano Unified School District in southern Orange County were closed on September 9. Most major universities and community colleges, as well as all federal courts in San Diego, closed for the day as well.[13]

The outage caused significant losses to restaurants and grocery stores, which were forced to discard quantities of spoiled food; perishable food losses at grocery stores, eating establishments and households were estimated at $12 million to $18 million.[14] The outage also caused some sewage pumping stations to fail, resulting in contaminated beaches and potentially unsafe water supplies in several areas.[15] As a precaution, in some neighborhoods, residents were told to boil their water or use bottled water for several days after the outage.[16] Due to the failure at the sewage pumping stations, diesel generators have been installed at five pumping stations.[17]

Question of association with terrorism[edit]

The outage occurred days before the tenth anniversary of the September 11 attacks, and hours before the United States Department of Homeland Security warned of a potential terrorist attack leading up to the anniversary, so that a first reaction to the blackout was to wonder if it might be the result of an attack. However, the Federal Bureau of Investigation and San Diego Gas & Electric ruled out terrorism early in their investigation,[18] and no subsequent evidence was found to suggest that the outage was anything other than accidental.


On April 27, 2012, the US Federal Energy Regulatory Commission and the North American Electric Reliability Corporation issued a joint report analyzing the technical details of the blackout and giving 27 findings and recommendations to prevent a recurrence.[19]

The initiating event was a procedural error made by a technician switching out a capacitor bank on a 500kV line at an APS substation in North Gila, AZ, causing the line to trip; it had been carrying 1,397 MW westward across California to Imperial and San Diego counties and CFE in Mexico. Electric utilities normally use advance planning and real-time computer monitoring and modeling to detect when such a single-point failure could trigger a cascading blackout, but none of the utilities detected that the system was vulnerable to the loss of this particular line. This began an 11-minute accelerating cascade of transformer, transmission line and generation trips. Ultimately, SCE invoked self-help and cut the state at San Onofre Nuclear Generating Station. There was some criticism that the threshold was too low, but it did prevent a larger collapse.

See also[edit]


  1. ^ Romero, Dennis (September 13, 2011). "Blackout Lawsuit Seeks Class Action Status in Federal Court For Millions Affected by SoCal's Electricity Outage". LA Weekly, LP. 
  2. ^ Ditler, Joe (September 16, 2011). "The Great Coronado Blackout of 2011". Coronado Eagle & Journal. 
  3. ^ a b c "Effects of power outage linger". San Diego Union Tribune. September 9, 2011. Retrieved September 18, 2011. 
  4. ^ Medina, Jennifer (September 10, 2011). "Human Error Investigated in California Blackout’s Spread to Six Million". The New York Times. p. A15. Retrieved September 10, 2011. "The day after the largest power failure in California history left millions in Southern California, western Arizona and northern Mexico without electricity during one of the hottest weeks of the year, local and federal officials promised Friday to investigate the cause." 
  5. ^ Baker, Debbi (September 9, 2011). "Power restored to all 1.4 million customers". San Diego Union Tribune. Retrieved September 10, 2011. 
  6. ^ a b c Watson, Julie (September 9, 2011). "Nuclear plant shut down in wake of outage". The Press-Enterprise (The Associated Press). Retrieved September 10, 2011. 
  7. ^ a b Morgan, Lee (September 16, 2011). "Outage had roots in Mexico, too". Associated Press. Retrieved September 26, 2011. 
  8. ^ Morgan, Lee (September 9, 2011). "Blackout sparks multiple investigations". Associated Press. Retrieved September 26, 2011. 
  9. ^ NRC Event Notification Report for September 9, 2011, Nuclear Regulatory Commission, September 9, 2011, retrieved September 18, 2011 
  10. ^ "Scripps Mercy probed after generator fails". San Diego Union Tribune. September 16, 2011. Retrieved September 18, 2011. 
  11. ^ articles.ivpressonline.com/2011-09-08/outage_30132657
  12. ^ Perry, Tony (September 9, 2011). "Power back for 694,000 customers of San Diego Gas & Electric, more on the way". Los Angeles Times. Retrieved September 10, 2011. 
  13. ^ a b "Normal life starts resuming after power restored in San Diego". Los Angeles Times. September 9, 2011. Retrieved September 11, 2011. 
  14. ^ "Despite losses, blackout may bring some good". San Diego Union-Tribune. September 10, 2011. 
  15. ^ "Power outage closes beaches and weakens grid". KPCC, Southern California Public Radio. September 9, 2011. Retrieved September 11, 2011. 
  16. ^ "Boil-water advisory lifted in San Diego neighborhoods". San Diego Union Tribune. September 11, 2011. Retrieved September 11. 
  17. ^ Artie Ojeda (8 September 2012). "San Diego Blackout: One Year Later". KNSD. Retrieved 23 February 2013. 
  18. ^ "Massive Power Outage in San Diego". International Business Times. September 8, 2011. Retrieved September 10, 2011. "Over 1.4 million people are suddenly without power in San Diego and surrounding areas in the Southwestern U.S. Thursday, just hours after Homeland Security warned of a possible terror strike in the days leading up to the tenth anniversary of 9/11." 
  19. ^ "Arizona-Southern California Outages on September 8, 2011: Causes and Recommendations".