A federal report released Tuesday probing the causes of the power outage that left San Diego County in the dark last September concludes that a lack of planning and poor communication by grid operators led to cascading outages.
The report—the culmination of a probe by the Federal Energy Regulatory Commission and the North American Reliability Corporation—issues recommendations to utilities and power operators on improvements they should make to prevent similar massive outages in the future.
With the blackout in the news again, it’s a good time for residents to consider whether they’ve made any emergency preparations since last September, when many found themselves in the dark, cut off from the world and resolving to get some batteries, flashlights and an AM radio.
The outage began the afternoon of September 8, when an Arizona Public Service 500-kilovolt transmission line went down, the report says. The line is a segment of the Southwest Power Link, a major east-west transmission line for power into Southern California.
“The loss of a single 500 kilovolt transmission line initiated the event, but was not the sole cause of the widespread outages,” the report notes. “The system is designed, and should be operated, to withstand the loss of a single line, even one as large as 500 kV.”
In fact, that major transmission line from Arizona into Southern California had been disrupted before, without major outages, the report says.
But with the transmission corridor down, power flows instantaneously redistributed throughout the region’s system, which increased flows through lower voltage systems to the north of the Southwest Power Link. At that point, power continued to flow into San Diego on a hot day during hours of peak demand, the report says.
But the redistribution of power created sizeable voltage deviations and equipment overloads in systems to the north of the Southwest Power Link, setting up a rippling effect that lasted about 11 minutes, with transformers and transmission lines tripping offline and shedding power loads.
There was minimal communication and awareness of the situation by power operators during this time, the report notes. Ultimately, excessive loading on a single power pathway carrying all flows into San Diego, as well as parts of Arizona and Mexico, triggered a mechanism that disconnected San Diego Gas & Electric from the power pathway and the San Onofre Nuclear Generating Plant, the report says.
That’s when San Diego residents saw their power go out. It was nearly rush hour, and traffic snarled as most signals failed and gas pumps stopped working. Cell communication was spotty, televisions and home internet didn’t work, and air conditioning was out on the hot day.
Power was restored locally as the night went on. But many residents realized how unprepared they would be for a more severe or prolonged emergency that left the roads impassable and communications compromised.
Fortunately, individual emergency preparedness hasn’t been tested again since September. We can’t predict; but we can prepare.
Residents can prepare for a blackout or other disaster by having flashlights and a radio with working batteries on hand, having at least one landline within the residence in the event that cell phones and cordless phones are not operable, and having 72-hours worth of supplies such as food, water and cash in the event of a major disaster.
For more information, visit www.sdcountyemergency.com and click on the readysandiego tab.
