It’s always silly to jump to big conclusions based on little information. Solar flares my ....
I don’t have complete or exact information so I can only form an opinion here based on the little information that is available. Since NERC and FERC are both looking into this, I don’t expect much information to be made public for a little while.
Yesterday afternoon, APS operators were alerted to troubles with a series line capacitor at North Gila substation. They sent substation personnel to switch the capacitor off line. Normally, this can be done easily through switches and circuit breakers placed in a way that allows them to bypass the bad equipment and isolate it from service without interrupting the power flow.
Something went wrong in this particular switching procedure, though we don’t know if it was human error or an equipment malfunction. At any rate, automatic fault sensing circuits tripped the 500 kV circuit on which this capacitor was connected out of service.
Normally, the power grid offers many parallel paths, and is designed and operated so that the loss of any single piece of equipment will not cause cascading outages on the transmission system. It appears that in this situation, that may not have been the case.
At 3:27 PM, the 500 kV line on which the misoperating capacitor was located tripped off line. Initially, everything seemed to be OK - other parallel power lines picked up the slack and continued to supply power to customers. However, by 3:38 PM, customers in Yuma, Arizona began to lose power. The outage apparently cascaded westward into southern California. Like APS in Arizona, those utilities also relied on a combination of local generation and a number of parallel paths into their respective systems.
Until we get more hard facts, I don’t think it’s possible to determine causation. I’m betting that when a good timeline is developed, we will see a number of contributing factors that played a role from the initial event in Arizona to possibly inadequate reaction to the situation, to a lack of preparedness for contingencies such as this, to competing planned equipment outages on the same day, to such things as improper tree trimming and maintenance.
It will all come out, but for now, it’s good that things are getting back to normal (or as normal as a big city in Southern California can be). I’ll keep my eyes open for more information - I have about 6 or 7 different articles plus some other scant information. It doesn’t seem like a lot of information is getting out yet at this time. With NERC & FERC involved, NOBODY will want to admit fault.