SAN DIEGO, CA - SEPTEMBER 8: Workers serve pizza to customers outside of Filippi's Pizza after a massive blackout hit Southern California September 8, 2011 in San Diego, California. Approximateely 1.5 million residents from Southern Orange County to Northern Baja are without power.(Photo by Sandy Huffaker/Getty Images)
Nearly two months have passed since a power outage wiped out power in much of Southern California and parts of Mexico, and the reason why is still unknown.
But authorities do know what happened, and discussed the cascade of events that led to the power outage that affected about five million people on September 8.
Several representatives from some of the electric utility and balancing companies attempted to explain the sequence of events which happened that day. They presented Wednesday to government leaders from the city and state as part of a hearing called “Addressing Grid Vulnerabilities: the Pacific Southwest Power Outage.”
The power representatives wanted the government leaders and public to know that one person did not cause the entire outage – even though one Arizona utility worker did trigger the chain of events which led to the outage.
“This event was not caused by a single utility worker. Our system is built to withstand that kind of error,” said Don Robinson of the Arizona Public Service Company.
A series of about 20 events occurred within 11 minutes of the Arizona transmission line failure, said Stephen Berberich from the California Independent System Operator (CalISO), .
Berberich explained the events in chronological order. When one of two Arizona transmission lines went out of service, the second also failed. This may have been due to an unusually high demand for electricity demand at the time of the outage in the Imperial Irrigation District.
About 20 seconds after that, a power plant in Mexico went out – but that appeared to be unrelated, he said.
Twenty seconds later, power went out in about a dozen other areas outside SDG&E and CalISO regions.
SDG&E learned of these outages about 30 seconds before they could do anything, according to Michael Niggli with SDG&E. After that, several other outages occurred – one of which at the San Onofre Nuclear Generation Station, which was taken offline as a safety measure.
Assembly members in attendance at the hearing were still frustrated with the various presentations from utility representatives.
“I feel less informed, and more confused,” said Assembly member Ben Hueso.
Members of the Federal Energy Regulatory Commission and the North American Electric Reliability Corporation are investigating the events, but could not say on Wednesday when they would be done with the report. They said they are still running tests. They may have a report within a year, they said.