Some overvoltage protection is by means of a crowbar circuit which will deliberately trip the breaker.
Yes, but that is used on the "client" side, not on the supply side. One could have a crowbar after each "client" circuit breaker but it would be a bit of overkill.
AFAIK crowbar circuits are only used to protect the avionics. For the other circuits, a short spike of overvoltage is not too bad, and continued overvoltage will trip the CB.
(but me too am sure G could improve on my words)