(09-10-2019, 11:50 AM)classicdrogn Wrote: Well, there'[s also the factor that cryogases are rather dangerous to be around let alone directly work with, added on to the expected issues of dealing with high voltage and current. Keeping a significant volume topped up with them would be expensive to operate as well, and depending on how much power it takes to run the support equipment might not even end up any better than conventional copper wires, though I'd want to see some numbers on that before even beginning to assert that such a conclusion is accurate.
It's not people actually perform work on energized high-voltage lines. The same applies here.
As for keeping the system "topped up" with cryogenic coolant, that brings us back around again to using liquid hydrogen as the coolant. Though volatile, it has the benefit of being lighter than air so it's easy to disperse.
Other cryogenic gasses are Helium isotopes, Nitrogen, Neon, Argon, Oxygen, and Fluorine.
Helium is prohibitively expensive due to its rarity. Neon and Argon are inert, but also present asphyxiation hazards in the event of a leak (and are expensive in large quantities). Oxygen is highly corrosive and makes any environment it's concentrated in into a literal powder keg. And Fluorine is just plain nasty. The only good thing about it is that it'd react and combine with everything nearby until there's no more left, making it (relatively) safe to clean up after the fact... but holy hell the damage it'd do in the process.
Nitrogen is about the safest thing to use - it's literally common as dirt and the common form (N₂) reacts with few things. But it would still present an asphyxiation hazard, and is otherwise useless in this application for anything other than a coolant.
Which brings us back to Hydrogen. Easy to produce, abundant, useful as an energy medium (fuel), and lighter-than-air so it doesn't collect and pool in low-lying areas. It is corrosive, but materials that safely contain and move hydrogen have been available for a substantial amount of time. And while highly flammable, this is also mitigated by its lighter-than-air properties, as well as careful anti-explosion measures (e.g.: use of brass tools, stringent measures to prevent electrical arcing, etc).
To mitigate damage from environmental factors, the infrastructure can be placed underground. Simply burying it will work and provide additional insulation, but I think it would be better to use tunnels that can act as carriers for other infrastructure (fiber optic, steam, water, sewage, storm drain) as well as improve ease of access to said infrastructure.
I have other ideas as well that would make such a project worthwhile, but that's best saved for another discussion.
As for numbers in the economic sense... I wouldn't know where to look, but I'd imagine that industries where cryogenic gasses are commonly used (e.g.: food preservation) would be a good place to start.