SUNDAY’S POWER OUTAGE FOR SDG&E CUSTOMERS WAS TRIGGERED BY GENERATOR OFFLINE IN SAN DIEGO, GRID OPERATOR CAISO SAYS

By Miriam Raftery

September 21, 2015 (San Diego)—On Sunday, as many as 90,000 SDG&E customers in San Diego County were without power for up to two hours.  As we reported, SDG&E tweeted that the outage was due to the California Independent Systems Organization ( CAISO) ordering SDG&E to “drop 150 MW of load in our service territory at around 1:15 p.m.” 

Today, CAISIO spokesman Steven Greenlee told East County Magazine that the problem originated locally.  “About 11:53 a.m. a generator in the San Diego area tripped offline,” he said.  With hot temperatures already raising demand for power, he said, “that generator overloaded the lines in the area.  That threatened to spread to other communities.” As a result, the ISO, which is above CAISIO and coordinates the entire western U.S. grid, serving as reliability coordinator, stepped in to protect the nation's power grid stability.

CAISIO then directed SDG&E to “controllably interrupt power for the entire service area,” Greenlee said.  “They began implementing a plan for rotating outages to prevent it from spreading and stop a larger outage.”

He confirmed that CAISIO did instruct SDG&E to reduce its load by 150 megawatts. “That enabled us to restabilize the grid.”  He said SDG&E’s emergency plan “did work.”  All outages ended by 3 p.m., according to Greenlee, and some may have been only a few minutes.

Greenlee declined to state the exact location of the failed generator or why it went offline, but stated, “The engineers are looking for the root causes at the moment.”

ECM reached out to ask SDG&E what caused the generator to trip and go offline, but the utility has not yet responded as of this evening.