Cascading Blackout Raises Grid Management Questions

By Published On: May 4, 2012

Transmission operators need to do a better job of sharing information about grid conditions and coordinating operations to prevent future cascading power failures, federal investigators stated in a May 1 report. It detailed the causes of the Sept. 8, 2011, blackout that left 2.7 million utility customers without power in Southern California, Arizona, and northern Mexico. “This report highlights the growing need for more coordination of grid operations in the West,” stated Federal Energy Regulatory Commission chair Jon Wellinghoff. The outage--initially blamed on an error that shut down a major 500 kV power line in Arizona--actually occurred due to a complicated series of events, according to the report by FERC and the North American Electric Reliability Corp. Electric Reliability vice president David Nevius called the blackout “one of the most complex electrical events in North America since the massive Northeast power outage of 2003.” A key cause of the blackout, he said, was the inability of various independent organizations that manage separate but interconnected parts of the Western grid to see what was going on in other areas. In effect, grid operators were making decisions in a partial vacuum. California grid operator chief executive officer Steve Berberich agreed with the report’s finding that more information sharing is needed to assure grid reliability in the West. The California Independent System Operator, he said, has been seeking more exchange of information and cooperation for years. Berberich said he hopes the report’s conclusions give new impetus to information sharing efforts. Five organizations managing various parts of the grid were involved, including Arizona Public Service, CAISO, Imperial Irrigation District, the Western Area Power Administration, and Mexico’s Comisión Federal de Electricidad. The Western Electric Coordinating Council coordinates their activities to maintain the overall reliability of the West’s interconnected bulk power system. That system stretches from Canada into Mexico between the Pacific Ocean and Rocky Mountains. The aim of the investigation was not to assign blame or find potential violations of legal requirements, said federal officials, but rather to draw lessons from the power failure that can help prevent future blackouts. However, federal officials did not rule out that a legal investigation may be underway. Federal standards require that the bulk transmission system remains operable when one major contingency occurs--such as the loss of a transmission line or power plant--explained Heather Polzin, FERC leader on the investigation. The loss of the 500 kV Hassayampa to North Gila line in Arizona, which tripped when an Arizona Public Service worker was performing maintenance, should not have led to a cascading outage, she said. Instead, according to Polzin, the outage stemmed largely from operating the transmission system in a way that it could not withstand the loss of the line on that day. FERC commissioner John Norris called on grid managers to use the lessons in the report “as a tool to improve their operations and planning of the grid.” Among the report’s findings are: -System operators have not adequately modeled the role that sub-100 kV transmission facilities play in the bulk transmission system, particularly in Imperial Irrigation District territory, which serves as a linchpin between Arizona and San Diego; -The Western Electricity Coordinating Council needs to review interconnection facility operating limits with an eye toward reliability; -Transmission owners and operators need to review overload protection relay settings to provide more time to take corrective steps when confronted with system overloads; -Transmission operators and the Western Coordinating Council need to review how special protection systems and measures--such as the San Onofre Nuclear Generating Station separation scheme--work under various scenarios to make sure they don’t have “unintended or undesirable effects” (see story above); and -System operators need to do studies that can allow them to more quickly re-energize transmission lines after outages. Federal investigators, according to Polzin, found that once the 500 kV line went down, the power it was carrying began to flow through smaller capacity Imperial Irrigation transmission lines rated at the sub-100 kV level. They quickly became overloaded and shut down, blacking out much of the Coachella Valley. As those facilities failed, the power increasingly flowed further to the west and then down Path 44, a series of five 230 kV lines between San Onofre and San Diego. Once those lines became overloaded, they automatically shut down isolating San Diego, northern Baja California, and Yuma, Arizona. Those areas quickly went dark when their limited local generation resources could not meet demand. Within 11 minutes, 2.7 million customers were without power. Federal investigators found that restoration of power went fairly smoothly. They credited system operators with preventing any damage to facilities. “It could have been worse,” said Nevius.

Share this story

Not a member yet?

Subscribe Now