A superconductor running at high amperage requiring more superconductor is still a superconductor. The losses you take are zero.
Any amount of cross-section of copper though is not - you take losses at (I^2)*R. You lose power as a square of the current.
There is an enormous difference between using superconductors at high currents and using any normal material.
Obviously the impact of this depends on what the critical current of a hypothetical room-temperature superconductor ends up being...but REBCO tapes achieve current densities of >40,000A/mm2 (at 77K). Depending on what you end up with, the expense and danger of maintaining the high voltage infrastructure could easily be seen as not worth it - particularly if it speeds up the ability to build out and maintain power lines.
Sure, but transission losses are generally a low single digit percentage-- eliminating those will not have much impact, but on the other hand your superconductor is EXTREMELY unlikely to be even close to cost competitive with aluminum/steel core wire.
Even if you could achieve critical currents comparable to conventional high-temperature superconductors at ambient temperature (which appears *highly* doubtful!), keeping high power transmissions lines at human-survivable voltages would be a tremendous waste of super-conducting material.
And even inside homes it seems quite farfetched to me to scale down voltages-- nobody wants to use plugs and switches rated for 200 amps just for their cheap toaster...
Yes, and for short haul that works fine. But for really long haul it doesn't, hence HVDC so that's what you compare with: the situation where it makes a difference such that extra cost incurred doesn't immediately invalidate your option. HVDC is much better comparison material than your average overhead powerline. For the same reason we don't compare bicycles with trucks for long haul cargo but we do compare bicycles with cars for shorter distances and personal travel.
NordLink flows 1400 MW. Wholesale electricity in Germany is roughly $105.
365x24x(1400x.07)x105 = $90 million per year. Adds up to the cost of the total project every 17-22 years. Over 20 years it's $1.8 million per km. If the superconductor is 20 kg/m (2.4" or 6.2 cm width, huge), that's $90 per kilogram.
10x the cost of copper.
Any amount of cross-section of copper though is not - you take losses at (I^2)*R. You lose power as a square of the current.
There is an enormous difference between using superconductors at high currents and using any normal material.
Obviously the impact of this depends on what the critical current of a hypothetical room-temperature superconductor ends up being...but REBCO tapes achieve current densities of >40,000A/mm2 (at 77K). Depending on what you end up with, the expense and danger of maintaining the high voltage infrastructure could easily be seen as not worth it - particularly if it speeds up the ability to build out and maintain power lines.