That's a recloser operating. Initially, there's a fault, say, a tree contacting a wire. This conducts a bunch of current to ground, the voltage in part of the

That's a recloser operating. Initially, there's a fault, say, a tree contacting a wire. This conducts a bunch of current to ground, the voltage in part of the network sags a fair bit, and a protective relay senses the overcurrent and opens the circuit. This happens in a second or two, and your power goes out. You may notice lights dimming or flickering in the instant beforehand. But, many faults are transient. Perhaps that tree branch finished falling, and is no longer against the wire. So the protective relay performs a "reclose" operation, where it turns the power back on for a moment and measures the current. There's normally a huge starting inrush as motor-driven appliances restart, so it waits a moment before sampling the current, and this is the period when the power comes back on for a few seconds. (It's probably pretty nasty power during this interval, too.) If things are good, hey, you're good! A brief outage while waiting for the fault to clear itself, and then everything's back. The operation will be reported to the dispatch center, and someone may come out to inspect the area in case there's damage. But if the fault is still there, and after a moment the current is still way higher than it should be, the recloser opens again, and this time it stays open. Gonna need a crew to move that tree, and then they'll manually try again.