The events that left 2.7 million power customers in Southern California, Arizona, and Baja California in the dark on Sept. 8, 2011, stemmed from operating in an unsecured state due to inadequate planning, a lack of observability, and awareness of system operating conditions on the day of the event, the Federal Energy Regulatory Commission (FERC) and the North American Electric Reliability Corporation (NERC) concluded in a report released on Tuesday.

Issued after a nearly eight-month inquiry, the report  recommends that transmission operators and balancing authorities improve how they plan for operations to account for the status of facilities outside their individual systems, the effect of external operations on their own systems and how operation of transmission facilities under 100 kV can affect the reliability of the bulk power system.

“This report highlights the growing need for more coordination of grid operations in the West,” FERC Chairman Jon Wellinghoff said in a statement. “Implementing the recommendations in this report will assist in enhancing the planning and system awareness measures that are necessary to operate an efficiently integrated bulk power system, and reduce costs to consumers from these types of outages that could continue if operational efficiencies are not improved.”

“This event underscores how complex and interdependent our North American electric systems are and the critical importance of information sharing, communications, system studies and coordinated operations among all interconnected systems,” said Gerry Cauley, president and CEO of NERC. “Transmission operators, Balancing Authorities and Reliability Coordinators must work together to effectively manage this complex system. I would like to recognize the effective collaboration between FERC and NERC staff during the course of this inquiry”

The inquiry was initiated to determine how the blackout occurred and to make recommendations to avoid similar situations in the future. FERC and NERC staff said they used “on-site interviews, sophisticated computer modeling, event simulations and system analysis” to make the determination that entities responsible for planning, operating and monitoring the bulk power system were not prepared to ensure reliable operation or prevent cascading outages in the event of a single contingency.

The cascading outages occurred on the afternoon of Sept. 8, 2011, after an 11-minute system disturbance occurred in the Pacific Southwest. All of the San Diego area lost power, with nearly 1.5 million customers losing power, some for up to 12 hours. The loss of Arizona Public Service’s (APS) Hassayampa-North Gila 500 kV transmission line initiated the event, but "was not the sole cause of the widespread outages," FERC and NERC said in the report. "The system is designed, and should be operated, to withstand the loss of a single line, even one as large as 500 kV."

The affected line is a segment of the Southwest Power Link (SWPL), a major transmission corridor that transports power in an east-west direction, from generators in Arizona, through the service territory of Imperial Irrigation District (IID), into the San Diego area. It had tripped on multiple occasions, as recently as July 7, 2011, without causing cascading outages.

The event exposed grid operators’ lack of adequate real-time situational awareness of conditions throughout the Western Interconnection, the report said. “More effective review and use of information would have helped operators avoid the cascading blackout. For example, had operators reviewed and heeded their Real Time Contingency Analysis results prior to the loss of the APS line, they could have taken corrective actions, such as dispatching additional generation or shedding load, to prevent a cascading outage,” the agencies said.

The report recommends that bulk power system operators improve their situational awareness through improved communication, data sharing and the use of real-time tools. It also recommends that:

  • System planners and operators recognize, study and incorporate the effects of sub-100 kV systems on bulk power system reliability into their planning and operations;
  • The Western Electricity Coordinating Council (WECC) recognize and study Interconnection reliability operating limits;
  • Transmission Owners and Operators review overload protection relay settings to give them more time to mitigate overloads;
  • Transmission Operators and WECC study the effects of special protection systems, remedial action schemes and safety nets, such as the one that disconnected San Diego from the high voltage lines south of the San Onofre Nuclear Generating Station, to understand how they affect reliability and to ensure that they do not have unintended or undesirable effects; and
  • System operators plan and account for phase angle differences in order to be able to re-energize transmission lines following outages.

Sources: POWERnews, FERC, NERC