5.3 Million People Lose Power Due to Routine Maintenance

People in San Diego and parts of Arizona and New Mexico lost all electrical power yesterday afternoon.  See links here and here.

The results?

Shut down of the San Diego Airport.
Huge traffic snarls (this occurred at around 4:00pm local time).
Shut down of 2 nuclear reactors (the shutdown was per procedure for a loss of load).
Over 1 million gallons of sewage spilled into the ocean due to loss of sewage treatment capability, closing San Diego beaches.

Was this caused by a huge lightning strike?  An enormous traffic accident?  A transformer explosion at a substation?  Nope.  In this case, it was a maintenance error.  A maintenance worker was changing out a piece of monitoring equipment, and for some reason (not yet determined) the power tripped.  Of course, there are safeguards that should localize this trip to a small area.  However in this case those safeguards did not work (not sure why), and a 500,000 volt power transmission line also tripped off-line.  This main feeder dropped power to a significant portion of the southwest U.S.

The company is initiating a root cause analysis to understand the reasons for the outage.