What's the most efficient for modern grids and electronics?
Would it be a higher frequency (1000hz)?
I know higher voltage systems are more dangerous but make it easier to transmit more power (toaster ovens in the EU are better because of 240v). I'm curious if we would pick a different voltage too and just have better/safer outlets.
> What's the most efficient for modern grids and electronics?
I do not think it is possible to answer the question as posed. It is a trade-off. Higher frequencies permit smaller transformers in distribution equipment and smaller filtering capacitors at point of use. On the other hand, the skin effect increases transmission losses at higher frequencies.
If you want minimum losses in the transmission network, especially a very long distance transmission network, then low frequencies are better.
If you want to minimize the size and cost of transformers, higher frequencies might be better. Maybe the generator is close to the user so transmission loss is less important.
If you want smaller end-user devices, high frequency or DC might be more desirable.
You have to define some kind of objective function before the question becomes answerable.
The losses over distance thing is the fundamental conflict between desired properties. For transmission you want as high a voltage as possible, but high voltage is both very dangerous and tricky to contain. So for residential use you want a much lower voltage. we picked ~ 200 volts as fit for purpose for this task. but 200 volts has high loses during long distance transmit. So having a way to transform the current into voltage is critical.
Some of our highest voltage most efficient long distance transmission lines are DC, but this is only possible due to modern semiconducting switches.
quadratically
This would be a pretty good approximation of the ratio of transmission lines to transformers.
>Generally, for long-distance power transmission, DC lines can be thinner than AC lines because of the "skin effect" in AC, which concentrates current flow near the surface of the conductor, making thicker wires less efficient; therefore, for the same power transmission, a DC line can be smaller in diameter than an AC line
This is especially a problem at high voltages and currents.
Also, DC arcs don’t self extinguish as well as AC arcs do, so DC arcs are a lot more dangerous and destructive.
It’s why HVDC lines are still relatively rare (and capital expensive), and typically used for long haul or under salt water, where the inductive loss from AC would cost more than the higher capital costs required for DC voltage conversion and stability.
or that it, itself, isn't a consequence of its own series of sunken cost fallacies
For instance, I would say that the scope of the global electrical grid includes every phone charger. Not just because the last foot devices are techically connected, but because they are the reason the rest even exists in the first place. So nothing that serves either the long haul or the local at the expense of the other can be called "minimal operational cost".
So trains use their own 25hz or even lower because that's good for long haul. But that would mean phone chargers are undesirably large and heavy. Or maybe it would mean that every house has it's own mini power station that converts the 25hz utility to something actually usable locally.
Meanwhile planes use 400hz 200v 3-phase for some mix of reasons I don't know but it will be a balance of factors that really only applies on planes. Things like not only the power to weight but also the fact that there is no such thing as mile long run on a plane, the greater importance to avoid wires getting hot from high current, etc.
Simply saying "the objective function is 'what is best?' and the scope is 'global'" doesn't turn an undefined scope and objective into defined ones.
Does this help you understand the original commenter's question?
You're asking how high is up.
240v is a good middle ground for safety and power.
Higher Frequency: Things that use electricity can be made smaller. But losses in long transmission become much worse.
DC instead of AC: Lower losses in transmission, don't need as much spacing inside electronics for arcing. But harder and less efficient to convert to different voltages.
Most Americans don’t drink tea and most coffeemakers heat water themselves. For most other applications using a pot on a stove is not a deal breaker.
Euro standards are 8-10A 240V circuits. I have an EU kettle, and it draws max 2200W.
US standards are 15A 120V circuits. It could draw 1800W, though some kettles might limit to 12A and draw 1440W.
So a Euro kettle might have 22%-52% more power than a US, which increases a 4 minute boil to 4m53s or 6m7s worst case.
So it seems like it's not a significant factor, though it would be useful if US kettles really maximize power.
Hrm, which country is that? Something between 13 and 16 amps is normal everywhere in Western Europe that I can think of, at 230V.
In Ireland, any random kettle that you buy is likely to be 3kW (pedantically, 2.99kW); you do sometimes see 2.2kW ones, generally _very_ cheap ones.
The Swiss outlets in my recent construction apartment were 8A. The standard allows a different outlet with higher amperage but I only ever saw that in commercial settings, similar to US 20A outlets.
That said, 2.2kW kettles definitely do seem to be more common there than here in Ireland (where 13 amp outlets are standard).
Our electric circuits aren't rated for 13A continuous draw (e.g. plug-in EV chargers should be set to 8A or 10A), but they are fine at 13A for the few minutes it takes to boil a kettle. 2.2kW kettles would be a major drain on productivity: millions of extra minutes spent every day waiting for a cup of tea!
Perhaps electric cars limit their draw below 13A as they're much more likely to be connected using extension leads.
> So why not use 400 Hz everywhere? Such high frequencies cannot be economically transmitted long distances, since the increased frequency greatly increases series impedance due to the inductance of transmission lines, making power transmission difficult. Consequently, 400 Hz power systems are usually confined to a building or vehicle.
* https://aviation.stackexchange.com/questions/36381/why-do-ai...
The NMEA2000 standard is confined to 12V however, meaning that all boats still need a 12V system as well. Maybe just with DC-DC conversion, or maybe with also a backup battery.
In reference to consumer power supplies, only reason why GaN power bricks are any smaller than normal is because GaN can be run at a much higher frequency, needing smaller inductor/transformer and thus shrinking the overall volume.
Transformers and inductors are often the largest (and heaviest!) part of any circuit as they cannot be shrunk without significantly changing their behavior.
Ref: Page 655, The Art of Electronics 3rd edition and Page 253, The Art of Electronics the X chapters by Paul Horowitz and Winfield Hill.
Short protection at the breaker for every circuit would probably be necessary at that voltage
I guess there’s some internal resistance or something, but…
Going to more than 20amp requires a multiphase circuit which are much more expensive and the plugs are unwieldy and not designed to be plugged and unplugged frequently.
There is no multi-phase power available in the vast majority of US houses. A typical residence has a 120/240 split-phase service, which is single-phase only. A service drop is two hot conductors from two of the three transformer phases and a center-tapped (between the two hot legs) neutral conductor. Either hot leg is 120v to ground and line to line is 240V.
> https://en.m.wikipedia.org/wiki/Split-phase_electric_power
Single-phase breakers are also available in sizes larger than 20A, usually all the way up to 125A.
The US could have toasters and hair dryers that work as well as European ones if everything was wired for 32A, but you only do that for porch heaters or electric vehicle chargers.
240V appliances typically get a 35 or 50A circuit.
But then you also have to deal with the fact that a lot of homes have wiring that can only handle 10A, but someone has replaced the glass fuse with a 20A breaker. Fun stuff.
I suspect some beauty products might also use 20A, or in combination easily reach that.
Most places with 240V regularly have 16A sockets, allowing a maximum draw of 3840W of power. That’s the limit. Cheap fast kettles will often draw 3000W and boil 250ml of water at room tempature in 30s.
Kettles in the US are often limited to 15A and thus max 1800W (usually 1500W) and take twice as long (60s)
Technology Connections has a great video on this: https://youtu.be/_yMMTVVJI4c
4.18 J/g/C * 250g * (1/ 20,000 kJ/s) * 75C = 3.918sOtherwise, you will very quickly vaporize the water near the heater and the resulting lack of contact will inhibit heating the rest of the water volume.
The trouble is the wires. A given wire gauge is limited in its ability to conduct current, not power. So if you double to the current, you'll need to have roughly twice as much copper in your walls, in your fuse panel, in your appliance, etc.
Additionally, losses due to heat are proportional to the current. If you double the current and halve the voltage, you'll lose twice as much power by heading the wires. For just a house, this isn't a lot, but it's not zero.
This is why US households still have 240V available. If you have a large appliance that requires a lot of power, like an oven, water heater, dryer, L2 EV charger, etc, you really want to use more voltage and less current. Otherwise the wires start getting ridiculous.
This is not to say that higher voltage is just necessarily better. Most of the EU and the UK in particular has plugs/outlets which are substantially more robust and difficult to accidentally connect the line voltage to a human. Lots of people talk about how much safer, for instance, UK plugs/outlets are than US plugs. If you look at the numbers though, the UK has more total deaths per year to electrocution than the US, despite the fact the US is substantially more populous. This isn't because of the plugs or the outlets, US plugs really are bad and UK plugs really are good. But overall, the US has less deaths because we have lower voltage; it's not as easy to kill someone with 120V as 240V.
So there's a tradeoff. There is no best one size fits all solution.
[1]: https://www.cpsc.gov/s3fs-public/Electrocutions-2011-to-2020...
By modelling the wire as an (ideal) resistor and applying Ohm's law, you can get P = I^2*R. the power lost in the wire is actually proportional to the square of current through it!
Therefore, if you double the current, the heat quadruples instead of doubling! You actually have to use four times the copper (to decrease resistance by 4x and get heat under control), or the wasted energy quadruples too.
Crucially, voltage is not in the equation, so high voltages - tens or hundreds of kilovolts - are used for long distance power transmission to maximise efficiency (and other impedance-related reasons).
Not sure about US, yet some high current lanes (thinks of threephase ~400V x 36A; IEC 60502-1) in the households are actually made of Al, not Cu. They tend to be underground though, the wires in the walls are still Cu.
Cu is more conductive than Al so an Al wire has to have a cross section area about 1.56 times that of a Cu with the same current capacity.
But Cu is also denser than Al so the Al wire is only about 0.47 times the weight of the Cu wire.
Al is is much cheaper than Cu so the Al wire is only about 13% the cost of the Cu wire.
Here is a table of the conductivity (in units of 10^7 S/m), the density, and the cost of copper (Cu), aluminum (Al), silver (Ag), and gold (Au).
Cu Al Ag Au
Conductivity 5.96 3.5 6.3 4.1
g/cm^3 8.96 2.6 10.5 19.3
$/kg 9.03 1.2 1030 92100
Weight Cost Diameter
Al 49 7 139
Ag 110 12646 97
Au 310 3190000 121* Currently using a cable spool which will have problems before blowing the fuse if it's wound up and I draw too much current. It has a thermal cutoff, but I still unspool some extra wire on the floor.
It would also make sense to have a high voltage and low voltage nets in houses. Low voltage for lighting and other low power equipment. High voltage for power hungry equipment. For example 48V and 480V.
DC or a significant frequency boost would be good inside a house for lights and electronic items. Not so great for distribution.
I'm not convinced multiple voltages would be a net benefit outside of the dedicated runs we already do for big appliances.
My grandfather worked in a Chicago office building that had 110V DC service even into the 1960s. He had to be careful to buy fans, radios, etc. that could run on DC.
Time will tell!
That'd be difficult; a breaker typically feeds an entire room, not a single outlet. (And when it does feed a single outlet, that's typically because it's dedicated to a specific large appliance, like an air conditioner or electric stove, which wouldn't benefit from being able to dynamically negotiate a voltage.)
One of the best things about living in the UK! https://www.youtube.com/watch?v=UEfP1OKKz_Q
Totally not, that would mean both worse skin effect and worse impedance. Likely the best option (if you really don't care about the existing infrastructure) would be DC, 0Hz. There are some downsides of DC, of course.
Almost everything complex does run on DC internally, but you feed those via AC adapters that then invert it to DC. You'd have to get bespoke DC-DC adapters (transformers, really) for everything.
DC (high) voltage to DC would skip the 1st few steps of AC->DC.
I always assumed it was just one induction and transformation step.
Lights, first and foremost. LEDs are DC.
> Almost everything complex does run on DC internally
almost everything runs on either 5V or 12VDC. What you would need are appliances that bypass the wall-warts/adapters and tap directly off DC, but this comes with some significant challenges. I'm already talking way outside my wheelhouse though, so I'll stop before I make a mockery of this topic.
Its very cool as a theoretical exercise and you could probably make a proof-of-concept house, but if you want to live in it and use literally anything non-bespoke, you have to convert DC to AC, which kind of defeats the purpose.
However, if that were worked out, you could have DC plugs in the house for all existing appliances and fixtures, and theoretically you would get a gain on both sides (no inverter, and no v-regulator (or a simpler, less lossy one)).
Then you wire your EV charger and big electrical appliances like stoves, ovens, microwaves, fridges (?), electric boilers, central AC, heat pumps, etc. into that DC circuit.
That alone would switch the majority of your electrical consumption to DC. Maybe long-term, you could have a special DC socket that you plug toasters, kettles, crock pots, vacuums etc in to, if they became available and cheaper.
Higher frequencies have terrible transmission (skin effect, transmission line length limit) and would start to interfere with radio.
Lower frequencies need larger transformers.
DC while nice is too expensive.
So about where we are now.
48VDC inside homes would be enough for most applications except heating and it would be kid-safe.
240V for heating applications.
Edit: Paulmann Velora are the expensive lamps at home.