This is actually the plot behind Larry Niven's Ringworld! A gigantic civilization has created a Ringworld (a rotating wheel artificial world), until a superconducting plague (https://news.larryniven.net/concordance/main.asp?alpha=S#sup...) destroys the material that enables room-temperature superconductivity, thus reducing the entire Ringworld to the dark ages...
Presumably the relay protection would trip the breaker for over current.
Essentially they would function like HVDC cables, and we already operate plenty of those.
Consider what would happen if the technology failed, and it suddenly transitioned to normal conduction.
Sounds like a great SF story, even if the actual effect is minimal. (I haven’t done the back of the envelope calculation :)