Outage Made Worse by Plant Shutdown

Wednesday, September 21, 2011 @ 06:09 PM gHale


The string of unplanned electric grid shutdowns that blacked out southern Orange County and San Diego this month ended up exacerbated when a power plant in Mexico, connected to the U.S. grid, protectively shut down.

The first power generating station to shut down after an equipment failure in Arizona was in Mexicali, where a natural gas-fired unit went off-line 20 seconds after the Arizona mishap, said California state officials.

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Stephen Berberich, the chief executive of California-ISO, which controls and switches power supplies in this state, said they do not know if the Mexicali plant shutdown was a part of the Arizona problem.

Javier Larios, regional superintendent for Mexico’s Federal Electric Commission, said the Mexicali plant went down so they could protect its components. The plant is one of several sources of energy in Mexico for consumers in San Diego, Riverside and Orange counties.

Two transmission lines feed electricity from Mexicali-area power plants north to the U.S.

The Mexican plant’s shutdown is one of 23 events on five separate but connected power grids that transpired in 11 minutes on Sept. 8. Once the dominos started falling, Cal-ISO officials at a ontrol room near Sacramento were not able to “ramp up” alternate power generators and prevent the blackout of 7 million customers of San Diego Gas & Electric, Imperial Irrigation District and Federal Electric Commission in Southern California and Baja California.

Other major electricity generators, including the San Onofre Nuclear Generating Station in northern San Diego County, also went into standby mode as power levels oscillated.

Such automatic shutdowns are necessary to prevent damage, but the Cal-ISO investigation will determine if they could have prevented the cascading failures.

Cal-ISO is reconstructing a “second-by-second” record of what happened after a switching error at an Arizona Public Service substation in Yuma, Ariz. started the cascading failures, Berberich said.



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