AC has no idea what hes talking about. this is a normal function of the electrical system. it worked as intended, there is no scare here.
A transformer blew, they do do that.
There were at least two other power supplies to feed the system, one being commercial, and in reality a non event. Being a nuke plant any thing out of the ordinary must be reported and scrutinized; as quoted "These events happen occasionally. They are not unheard of and the plant responded as designed," in this case the auto sprinkler system took care of it.
Wanna bet what the people working at the plant did? My guess is whenever they could went to look at it, no cares at all just curiosity.
If it's power was being utilized at the time, it was switched so fast the computers never knew; well maybe a stretch (but they are on UPS systems).
As a general rule for Nuclear plants there are three systems for each function, one goes down another takes it's place, another goes down which is providing the same function it's time for concern (dependent only upon it's function). Fukushima used the fourth option (firetrucks).