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0 pointsXorNot2y ago0 comments

> We might eventually transition away from AC power entirely.

This is actually a really good point I hadn't fully considered, but it's right: the primary reason we use high voltage anywhere is because it minimizes resistive losses (and the reason we use AC is because it's easy to transform between voltages).

But most of the stuff in my home doesn't need high voltage - it's all running at 5V or 12V. Or it's a motor which is magnetically driven and depends solely on magnetic field strength (which is independent of voltage).

If all your conductors have zero resistance, then high voltage is obsolete. You could safely run a residential property on 12V power. Home electrical hazards would a thing of the past.

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6 comments · 4 top-level

myrmidon2y ago· 2 in thread

This is drawing completely wrong conclusions from erroneous oversimplifications:

We're using high transmission voltages to keep current down. Superconductors would not change this AT ALL; superconductivity generally breaks down not only with temperature increases but also magnetic field strength (i.e. current).

Switching large currents is also a hassle; especially with non-resistive loads.

And completely changing household electricity architecture is simply not gonna happen just to marginally improve safety, cost/benefit ratio is WAY too high.

XorNotOP2y ago

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.

myrmidon2y ago

> The losses you take are zero.

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...

2 more replies

jacquesm2y ago

It's interesting to see how many assumptions about our world are underpinned by the lack of superconducting material. That also immediately gives you an idea of how transformative (heh.) room temperature superconductors would be.

hwillis2y ago

> But most of the stuff in my home doesn't need high voltage - it's all running at 5V or 12V.

85 volt DC carries the same power as 120 volt AC, but 85 volts DC is essentially safe to touch. The human body has a much lower AC impedance, so it's MUCH more dangerous. DC does still hurt, though.

40-80 volts (see also: split phases) DC is very convenient for most electronics. It's really just things with batteries that want 5-12 volts, but stepping that down isn't too hard.

At the grid scale, it's a question of which is cheaper. If the infrastructure becomes much more expensive (because the wires are SC) then you can save money by using DC (which gives you 41% more power). If its cheaper to use transformers than it is to use more superconductors and semiconductors to convert voltages, they'll do that.

Either way the grid would stay relatively high voltage (10s of kV), because it's just always going to be worth it at that scale to minimize the conductor area.

Workaccount22y ago

We use AC because changing voltage levels with it is extremely simple and efficient compared to DC.

In fact the only (practical) way to convert DC voltage levels is to convert to AC, do the level conversion, then convert back to DC.

Believe it or not, DC already is more efficient for energy transfer and why there are already DC high voltage transmission lines. You don't have to deal with reactive parasitics.

But again the killer is that AC voltages are so easy to switch and can by done with >99% efficiency.

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