Some circuit in the power grid approached its overload point. Whether that overload was due to excess demand, or a piece of hardware that actually failed, is so far uncertain. But it’s clear that somewhere, demand exceeded capacity and a circuit went down.
At that point, the grid automatically re-routes current from elsewhere to supply the demand. Which means that now some other circuit is being asked to supply current to its own load, plus this excessive load from the first circuit. This causes the second circuit to go offline (again, ideally via circuit breaker, but possibly via hardware failure).
This morning on NPR, a professor from Drexel was on the phone explaining why we weren’t affected by this failure. I couldn’t make out his name, nor could I properly pronounce/spell it even if I knew it; as you might expect, understanding his explanation wasn’t easy. But I gathered that somewhere in Valley Forge (PA), there is a mechanism that detaches "us" from the part of the grid that went down. I don’t know whether that’s automatic or manual, but apparently that happened, and it isolated us from the problem.
Whatever caused the initial circuit failure -- whether it was a hardware failure, some sort of sabotage, or simply excess demand -- isn’t particularly interesting to me. What I want to know is why the detachment that happened at Valley Forge didn’t also happen in lots of other places. If the power grid can be sectioned off that way, then it seems to me that the sections should be considerably smaller than the size of 6 states plus some of Canada.
