The AC/DC debate has raged for over a hundred years because each side has some merits over the other, but overall the differences are relatively minor compared to the cost of ripping up an existing AC or DC system and replacing it, or even switching to one system or the other going forward. PG&E isn't going to scrap all of the transmission towers they have on order just because DC might save them a few dozen watts.
Why DC May Replace AC (2019)
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Re: Why DC May Replace AC (2019)
#72I can't find the date this article was written. Is it 20 years old or 2 days old?
Re: Why DC May Replace AC (2019)
#73Earlier quoted context omitted.
> The required converter stations are expensive and have limited overload capacity. At smaller transmission distances, the losses in the converter stations may be bigger than in an AC transmission line for the same distance. The cost of the converters may not be offset by reductions in line construction cost and lower line loss. https://en.wikipedia.org/wiki/High-voltage_direct_current#Di... Not to mention that circu…
> Not to mention that circuit breakers are harder in DC. [Citation needed]
I can believe this is true. It's easier to make reliable AC switches because whatever arcing you get is self-extinguishing because the voltage passes zero 120 times a second. With DC, if you get an arc it'll just keep going as long as conditions allow. That means if you use a designed-for-AC switch in a DC application with the same voltage, it's likely to destroy itself sooner or later.
(Apparently this is one of the reasons why cars stick with 12V for accessories, because if they used higher voltages the electrical switches would be more expensive and less reliable.)
I don't know how this is normally overcome. In a lot of cases, the solution might just be "use a fuse instead".
Re: Why DC May Replace AC (2019)
#74Earlier quoted context omitted.
Right, agree. But then there is the tradeoff of the popularity and availability of 12VDC devices due to RV/Boating. But strictly from a technical point of view you are spot on.
> But then there is the tradeoff of the popularity and availability of 12VDC devices due to RV/Boating. Which is exactly why we need to get away from those 12V old garbages asap. 12V is so bloody wasteful, in terms of both wasted power and wasted conductor material. The only reason why its still around is people got used to it and don't wanna change.
what is the optimal voltage based on empirical data ?
Re: Why DC May Replace AC (2019)
#75For safety alone DC is not going to replace AC. The author seems to be confusing local use, and distance transmission.
In what way is AC safer than DC? Ohm’s law says V=IR, that means your resistive body is gonna get shocked regardless of whether the voltage is constant or changing.
Don't forget that AC can flow through capacitors.
Re: Why DC May Replace AC (2019)
#76> In China and Europe, new cities and villages are being envisioned that will be entirely DC powered. Citation needed? Other then HVDC links or micro-generation I can't see a practical use for DC unless you are entirely off-grid.
lots of things are envisioned every day. everyone has ideas; calling it "envisioned" doesn't make those things any more feasible or realistic. article author is either sole owner of a huge copper deposit or isn't articulating themselves very well. DC makes no sense for distribution at all.
But DC is used for distribution, just at extremely high voltages.
Re: Why DC May Replace AC (2019)
#77Earlier quoted context omitted.
lots of things are envisioned every day. everyone has ideas; calling it "envisioned" doesn't make those things any more feasible or realistic. article author is either sole owner of a huge copper deposit or isn't articulating themselves very well. DC makes no sense for distribution at all.
But DC is used for distribution, just at extremely high voltages.
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Re: Why DC May Replace AC (2019)
#78There is some validity to using DC distribution within a building or domicile, it can make it cheaper and more reliable to have a central power supply and battery system. That is not a new idea obviously, that exact approach has been in use in the telecom industry for decades. There is a AC feed to a system of rectifiers that converts the AC from the grid to -48VDC and continuously charge a string of batteries. There…
Correct me if I'm wrong but isn't the whole point of using AC that it's easy to convert voltages super-efficiently with transformers?
Having DC power at home seems like the worst of both worlds. Low voltage DC at home causes large losses in the wiring, and high voltage DC causes large losses in the step-down regulator (leaving you with a buck-type regulator operating at the low extreme of its duty cycle). After all, DC-DC conversion relies broadly on turning the DC into something vaguely sinusoidal and using an inductor - so its basically DC-AC-DC anyways.
Am I missing something?
Re: Why DC May Replace AC (2019)
#79The author seems very confused about whether they're talking about the grid or devices. "DC power is significantly more energy efficient than AC power." -> the examples go on to specify end points for electrical energy but we already use DC there, AC is mainly used in transmission, so the claimed advantages of DC are irrelevant. "DC motors and appliances have higher efficiency and power to size characteristics." -> B…
If you wanted to efficiently make an efficient deeply variable speed modern motor run on AC, you might very well turn the AC into DC then back into AC in a brushless motor controller.
Indeed, changing the frequency of an AC wave programmatically is incredibly difficult (but possible through a CVT, I guess), you're better off turning it into DC then back into AC through some some form of function generator.
So indeed, the widespread use of BLDC motors is a point in favour of DC electric circuits in the home.
Same goes for variable velocity generators, you will generally have an AC-DC-AC conversion in a variable speed generator. Either that, or a gearbox, those are your two options.
Re: Why DC May Replace AC (2019)
#80Earlier quoted context omitted.
AFAIK wind turbines, as opposed to conventional turbines in power plants, don't directly connect to the 60Hz Grid but go through DC and an inverter. This is done so they can efficiently work at different speeds at not just a few mechanically selectable ones
They have to, because the variable wind means that they need to be spinnable at a continuous range of speeds. Components connected to the AC grid need to synchronize with the grid's frequency. Since we can't force the wind to blow at a particular rate, we'd either need a lot of fancy mechanics on the turbines themselves to drop their speed (which would waste energy) or we decouple their spin rate from the grid freque…
You could also have a continuously variable gearbox, which is still hugely problematic, but would waste less energy.