Is there anything special about it? Or is the actual switching just done by a beefy IGBT?

Much faster detection of fault, including ability to detect and point to a fault happening at a distance from the relay.

Yeah, the story I remember being told is that power companies originally didn’t want to replace their electromechanical relays so they installed the SEL boxes alongside them and used them as fault locators.

Over time SEL ended up taking over the market though.

They haven't completely taken over the market. The likes of Siemens, ABB, GE, etc. manufacture similar products. SEL is considered the best by many utility engineers.

From what I recall, SEL’s market share was high enough in the US that almost all of our growth was international.

So it's a big solid state transistor rather than a relay?

Man, I don’t know how electricity works, I was writing test scripts in Perl.