2011 Southwest blackout

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]

Effect

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.^[9] 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).^[10]

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.^[11]

Aftermath

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] All public schools in San Diego County and some in Orange County were closed on September 9 as were major universities, community colleges, and the Federal court system.^[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]

Question of association with terrorism

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,^[17] and no subsequent evidence was found to suggest that the outage was anything other than accidental.

Report

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.^[18]

The initiating event was a procedural error made by a technician switching out a capacitor bank on a 500kV line at a 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 a 11-minute accelerating cascade of transformer, transmission line and generation trips culminating in the disconnection of the main transmission path carrying power southward into San Diego from the San Onofre Nuclear Generating Station and points north.

See also

• 1996 Western North America blackouts
• California electricity crisis
• Northeast Blackout of 2003
• Path 46, also called West of Colorado River, Arizona-California West-of-the-River Path (WOR)

References