Will AC power distribution become obsolete?

[schmitt trigger]

This hairy old chestnut.

DC power over very long distances is practical and efficient,  but not for final distribution.

The thing is that there are those who have little understanding of the technicalities and safety aspects in letting Joe public near high energy DC.

Why would it need to be high voltage? Joe Public won't get electrocuted from 30 volts. That's what I meant by safety, if you had read my post.

By now I think you are trolling...
Over and out..

Either that, or the TS has a severe lack of understanding of basic electrical theory.
Most likely he is a troll.

[tooki]

Edison lost the war of the currents to Westinghouse and Tesla because his DC current couldn't be transformed to the higher voltages required for long range transmission. Alternating current, however is more difficult to use, once it gets to it's destination. A single-phase AC motor was a difficult engineering problem, and to this day is less efficient than either DC or 3-phase AC.

I think the issue wasn’t in converting it up (because you could just generate it at a higher voltage), but converting it down to the voltages needed at the consumer.

But DC power can now be transformed to higher or lower voltages without transformers. Solid state converters have become ubiquitous and relatively cheap. For example, fast-charging in your smartphone is accomplished by raising the voltage in the cable, allowing more power to be transferred without exceeding the current capacity of those small wires.

Right. And this alone should explain why moving to even lower voltages would be stupid: wires get thicker and thicker.

Heck, we are at the point where DC-DC converters are so commonly placed right at the load on a PCB that newer PC motherboards no longer receive anything but a 12V input. No more 5V and 3.3V rails, with their correspondingly higher currents.

In other words: we are now better positioned than ever to use HIGHER voltages and convert them on the spot.

And indeed that’s exactly what we’ve been seeing, like USB going from 5V to now all the way to 48V.

Your 30V DC fever dream is never going to happen, because we’d need insane amounts of copper (and no, going to silver wouldn’t make this problem go away) and absurdly chunky switches and circuit protection devices.

All to get rid of AC, which isn’t even a problem. You know that converting AC to DC is a problem we solved over a century ago, right? Taking AC mains and turning it into a safe (=galvanically isolated) low-voltage DC output is no harder than doing it from DC, and in fact can be easier.

[TimFox]

The OP is returning to old territory, where his pointless rant about UK plugs rapidly turned into pointless argument about 30V DC distribution in the home. It didn't end productively last time, I can't see him understanding any better this time...

https://www.eevblog.com/forum/chat/grumpy-rant-783/msg5102037/#msg5102037

In his previous topic, he never answered how 30 V DC distribution would help the 3000 W teakettles that are common in the UK.
One of the proposed reasons for Brexit was an allegation that the EU would ban kettles at that power range, so we may conclude that the OP is a stalking horse for EU regulations.
At 240 V, 3 kW is only 12.5 A (which is practicable), but at 30 V it would be 100 A, requiring roughly AWG 0 (53 mm² area or 8.3 mm diameter) copper wire cordage.
When presented with a new idea, it is always useful to quickly analyze it for extreme, yet practical, conditions.

[tooki]

This hairy old chestnut.

DC power over very long distances is practical and efficient,  but not for final distribution.

The thing is that there are those who have little understanding of the technicalities and safety aspects in letting Joe public near high energy DC.

Why would it need to be high voltage? Joe Public won't get electrocuted from 30 volts. That's what I meant by safety, if you had read my post.

By now I think you are trolling...
Over and out..

Either that, or the TS has a severe lack of understanding of basic electrical theory.
Most likely he is a troll.

I think both. In one of his early posts, he outright states that he doesn’t know much about electricity, and their post history show a consistent lack of understanding, combined with unwarranted confidence and “I have this great solution to a problem Everyone Else™ is too dumb to think of” nonsense.

[themadhippy]

At 240 V, 3 kW is only 12.5 A (which is practicable), but at 30 V it would be 100 A, requiring roughly AWG 0 (53 mm2 )

53mm² for 100A?  25mm² is more like it,

[TimFox]

Wire tables vary, but that is what I found in one normal table for AWG/mm² values as a safe (not fusing) value for 100 A.
It depends on how hot you are willing to get the wire.
The other extreme to my tables is specifically for 2% drop of 220 VAC (single phase) for 25 feet in conduit:  AWG 8 or 3.26 mm diam = 8.4 mm².
However, that's for 2% of 220 V = 4.4 V, which would be a big chunk of 30 V.

[IanB]

The power cord on my 3 kW kettle has 1 mm2 conductors for 13 A, although the manufacturer was cutting costs, and 1.5 mm2 would have been more suitable.

This cord gets slightly warm, but barely detectable, when the kettle is operating. And I don't know what the voltage drop is.

By simple scaling you could probably get away with 10 mm2 for 100 A, if the voltage drop was acceptable.

[soldar]

Wire tables vary, but that is what I found in one normal table for AWG/mm² values as a safe (not fusing) value for 100 A.
It depends on how hot you are willing to get the wire.
The other extreme to my tables is specifically for 2% drop of 220 VAC (single phase) for 25 feet in conduit:  AWG 8 or 3.26 mm diam = 8.4 mm².
However, that's for 2% of 220 V = 4.4 V, which would be a big chunk of 30 V.

But we would be using silver instead of copper
https://www.eevblog.com/forum/chat/why-not-silver/

[David Hess]

Alternating current, however is more difficult to use, once it gets to it's destination. A single-phase AC motor was a difficult engineering problem, and to this day is less efficient than either DC or 3-phase AC.

The problems of single phase motors are irrelevant because they are only used at low power levels.  Big motors are three phase, and the third wire in a 3-phase system triples its capacity.

But DC power can now be transformed to higher or lower voltages without transformers.

Transformers are still used in DC to DC conversion for isolation and efficiency.

About a mile from here there is a DC transmission line, running at 500,000 volts. The higher the voltage, the lower the amperage, which reduces power loss through heat. This used to be accomplished by using transformers which required AC, and significant power losses were always a factor. Now with high voltage DC, this is much less of a problem. Not only is only 1 conductor required instead of 3, it's also easier to convert power than with the old, bulky and inefficient transformers.

Low frequency AC transformers are generally more efficient than DC to DC conversion.  Transformers can always be made more efficient at the cost of more materials, size, and weight.

Did you ever wonder why DC links are used for the highest power long range power transmission when the AC voltage could have been further increased.  Corona losses are proportional to some power of the voltage, so above some voltage corona losses of DC transmission are less than AC transmission for a given power.  DC of course also avoids the problem of AC grid synchronization which must take place in one way or another.

So why do we need AC in our homes? We don't. A house could be supplied with DC power from the mains, and converted to any type of power we could require. Imagine a future where DC power receptacles are installed in a house, at a safe voltage, where electrocution is impossible, and converters simply transform the safe current into anything that is required. Synchronization between solar power and grid power will be much simpler than it is now. It takes some sophisticated equipment to synchronize AC circuits together. With DC, it's a much simpler matter.

High voltage DC will electrocute you just as fast as AC.  AC at endpoint voltage levels has the advantage of self extinguishing arcs.  An equivalent infrastructure for DC has special requirements for switches, connectors, fuses, and circuit breakers to do what AC gets for free.

I likely won't live to see it, but I foresee a world of ubiquitous, safe, DC power in the future.

That world will also include lower reliability, higher cost to repair, higher cost, and likely lower efficiency.

[TimFox]

Oh brave new world, that has such features in it!
(slight change to Shakespeare's Tempest)

[coppice]

The power cord on my 3 kW kettle has 1 mm2 conductors for 13 A, although the manufacturer was cutting costs, and 1.5 mm2 would have been more suitable.

1mm2 is fine for a 3kW kettle, unless you are using the kettle in a very unusual way that keeps it running for long periods, or you heavily insulate the wire. Intermittent use wiring is not usually rated in the same way as continuous use. I wouldn't use 1mm2 wire for a 3kW laundry dryer, for example.

[IanB]

Well, indeed. Even my expensive Tefal kettle has a 1 mm2 power cord. It seems it must meet consumer product requirements.

[Someone]

Well, I will say this: we have the technology to do it, today.

We won't do it, probably in the next half-century, and maybe not ever, because of extenuating factors:

1. Mains distribution must be robust.  It is exposed to direct lightning strike, nearby (induced) strike, arcing due to crossed wires, tree falls, switching (especially inductive) loads, etc.

2. It must be able to source massive currents, to start rotating machinery, clear fuses, etc.  High surge capacity is, in one respect, a passive safety feature.

3. There is another passive safety afforded by AC: arcs are somewhat self-extinguishing.  DC arcs are notoriously hard to put out.  This reason, alone, may well be sufficient to never adopt a DC distribution system!

AC ground currents also don't cause corrosion -- indeed, it's not even a rare occurrence, as I understand it, for an underground substation (vault) to flood with water -- at least as long as it's not sea water I suppose (but maybe even then!), these can just keep on operating, at higher power loss perhaps, but corrosion is negligible, and not much special material or coating is required of the conductors and switches in these installations.

4. I don't have any idea if the semiconductor cost will come down in the future, or how it can come down in some best-case scenario, and if so by how much -- but at least given current top materials (SiC and GaN), replacing a simple wall switch takes about as much semiconductor solid, plus packaging, to handle the same ratings as a mechanical switch.  Similar proportions apply to everything else handling power: relays, breakers, transformers (--> converters), tap switchers (would be obviated by converters, at least), etc.

Pretty comprehensive, I'd add that breaking DC is much harder than AC due to the sustained arcing. An issue all the way from the consumer outlet (USB-PD in the 3.1 revision for 100W+ power includes specific protections for this) through the distribution. HVDC distribution has come "down" in cost and increased application, but I can't see it making sense at the domestic level for decades to come. Transformers and fuses are just so cheap and reliable.

[Someone]

But DC power can now be transformed to higher or lower voltages without transformers.

Citation required! Pretty much all mains SMPS units do use a transformer (or at least an inductor) with high frequency AC.

[coppice]

But DC power can now be transformed to higher or lower voltages without transformers.

Citation required! Pretty much all mains SMPS units do use a transformer (or at least an inductor) with high frequency AC.

We typically use a transformer because we actually want a transformer for galvanic isolation. Otherwise we use an inductor. You just need something to store the in-flight energy.

[Someone]

But DC power can now be transformed to higher or lower voltages without transformers.

Citation required! Pretty much all mains SMPS units do use a transformer (or at least an inductor) with high frequency AC.

We typically use a transformer because we actually want a transformer for galvanic isolation. Otherwise we use an inductor. You just need something to store the in-flight energy.

You know that, I know that. But the OP makes out like HVDC will eliminate transformers. Lots of things are possible but that doesnt mean they make sense.

[TimFox]

The power cord on my 3 kW kettle has 1 mm2 conductors for 13 A, although the manufacturer was cutting costs, and 1.5 mm2 would have been more suitable.

1mm2 is fine for a 3kW kettle, unless you are using the kettle in a very unusual way that keeps it running for long periods, or you heavily insulate the wire. Intermittent use wiring is not usually rated in the same way as continuous use. I wouldn't use 1mm2 wire for a 3kW laundry dryer, for example.

Note that your 3 kW at 240 V is only 13 A.
If the suggestion for 30 V DC were adopted, the current would be 8x higher, and the allowed voltage drop 8x lower, requiring 64x less resistance and 64x more cross-section area for equivalent performance.

[NiHaoMike]

I can see it going obsolete for lighting, it just makes sense to run a lot of LEDs from a single DC supply, most likely 48V. No flicker and dimming would be excellent.

[David Hess]

We typically use a transformer because we actually want a transformer for galvanic isolation. Otherwise we use an inductor. You just need something to store the in-flight energy.

A transformer is also used when the conversion ratio is high or low to move the duty cycle closer to 50% because very small or very large duty cycles are problematical.  In some cases a tapped inductor can do the same thing, but this is less common than using a transformer.

[Connecteur]

If I were to guess, it will probably come in stages.  The same high tension lines that carry AC could probably carry HVDC.  The transformers will have to be replaced with solid state converters.  Once in the home, it can be converted to a variety of useful voltages, probably not as hazardous as our current outlets.  I don't know which protocols will be established, but some will be for electronics and others will be for power appliances, I imagine.
Of course this is all a ways off, and probably beyond most of our lifetimes, but I definitely foresee the end of AC power.

[Connecteur]

But DC power can now be transformed to higher or lower voltages without transformers.

Citation required! Pretty much all mains SMPS units do use a transformer (or at least an inductor) with high frequency AC.

I don't claim to know for sure, I just made an educated guess. 
Don't throw "citation required" at me again.

[tooki]

But DC power can now be transformed to higher or lower voltages without transformers.

Citation required! Pretty much all mains SMPS units do use a transformer (or at least an inductor) with high frequency AC.

I don't claim to know for sure, I just made an educated guess. 
Don't throw "citation required" at me again.

I suspect that a great deal of the ”facts” you think you know are, in fact, guesses — both educated and uneducated. It’s great that you wonder about things. Curiosity is awesome. But don’t make the mistake — which we have seen with some other members who posted similar types of threads in the past — of ignoring what others with more education and experience have to tell you. (One of them I described as “filling in the gaps in their knowledge with delusions, and then treating those as canon.”) Their education and experience trump your guesses. This forum is a gold mine of electronics education by highly qualified people whose knowledge you’d pay through the nose for if you had to pay tuition or consulting fees to talk to them. Avail yourself of it instead of trying to outsmart them.

P.S. Yes, transfomerless DC-DC converters do exist (like the common buck, boost, and buck-boost converters using inductors, and switched-capacitor voltage boosters). But that doesn’t mean they are ideal for every situation. As I and others have said, galvanic isolation is a desirable (or required!) characteristic in many situations, and transformers are one of the few ways to achieve this.

[nctnico]

It would help if there was some kind of standard for low voltage DC power connectors.

That's a very honourable idea, but trying to implement it will just create another connector, not replace any.

That connector already exists: USB-C and supports up to 48V @5A . Voltage is negiotated so every device from earphones to a big laptop can be charged / powered from the same outlet.

[Gyro]

If I were to guess, it will probably come in stages.  The same high tension lines that carry AC could probably carry HVDC.  The transformers will have to be replaced with solid state converters.  Once in the home, it can be converted to a variety of useful voltages, probably not as hazardous as our current outlets.  I don't know which protocols will be established, but some will be for electronics and others will be for power appliances, I imagine.
Of course this is all a ways off, and probably beyond most of our lifetimes, but I definitely foresee the end of AC power.

The only place where 'grid scale' DC conversion does make sense is for international bidirectional import/export interconnects, typically sub-sea cables. These remove the need for absolute frequency and phase locking between the two countries. [EDIT: Oh, and offshore windfarms.]

About a mile from here there is a DC transmission line, running at 500,000 volts. The higher the voltage, the lower the amperage, which reduces power loss through heat...

In that case, I suspect that you live within a few miles of the coast. 500kV AC transmission lines are common BTW, nothing special about the voltage.

[Kleinstein]

There are quite some induction motors, especially in commercial uses. They are cheap, reliable and robust, but they need AC, ideally 3 phase. An extra inverter adds quite some costs and EMI problems.
Even the universal motors don't like DC that much and would need a different (lower) voltage. Existing speed control eletronics usually is based on SCRs of some kind and thus also only works with AC.

Low voltage DC (like 48 V) is not practical for the distance from a mains transformer to the houses. Higher voltage DC (like used with PV) is tricky with fuses. There is less danger from electrocution, but more danger from a persistant spark to create a fire or let fuses or switches fail. There is a reason that the DC ratings for switches / relays is quite a bit lower than the AC rating.

Some may opt for an extra in house DC network at a lower voltage for low power devices and maybe lights.