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Why DC May Replace AC (2019)

electricalindustry.ca

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Re: Why DC May Replace AC (2019)

#61

Post by distortedsignal »

elihu wrote: post #52
Arainach wrote: post #47

Earlier quoted context omitted.

https://www.youtube.com/watch?v=S7C5sSde9e4&t=3m18s https://www.youtube.com/watch?v=S7C5sSde9e4&t=7m34s The thermal properties of AC for comparable amounts of power in a conductor are significantly better. Copper is expensive, and having dealt with just the difference between connecting 12 gauge and 14 gauge to outlets and pulling it through conduits I'm certainly not enthusiastic about needing larger conductors.

He was running ten amps over thin wires; of course that doesn't work. The problem there was that he was transmitting significant power at low voltage and high current. That doesn't say anything about the superiority of AC or DC. AC has historically been the more practical choice because you can trade AC voltage for current easily with a transformer, but there are ways to do that with DC now too. Maybe there's an argu…

> 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 circuit breakers are harder in DC.

Re: Why DC May Replace AC (2019)

#62

Post by dhdc »

WorldMaker wrote: post #12
sabareesh wrote: post #6

Earlier quoted context omitted.

I don't think it is efficiency, we had no way to step up and step down DC as we can do AC

Yup, transistors especially have given us major breakthroughs in the ability to step up/step down DC. Also, there have been huge breakthroughs in High-Voltage DC: https://en.wikipedia.org/wiki/High-voltage_direct_current At certain huge (grid) scales they have found that AC and DC swap "efficiencies" again and we're increasingly starting to see current flows as DC-AC-DC "sandwiches" with DC used by the majority of co…

> DC-AC-DC "sandwiches"

Couldn't have said it better, I had a good laugh.

Re: Why DC May Replace AC (2019)

#63

Post by cfraenkel »

thehappypm wrote: post #55
Overtonwindow wrote: post #51

For 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.

It isn't - both can kill you. DC results in a continuous muscle contraction, where AC makes for many contractions; DC 'let go' current is higher than AC; lethal AC current is also lower than DC. But we're talking mA here - house current will kill either way if it goes through the heart. source: https://www.brighthubengineering.com/power-plants/89792-ac-a...

Re: Why DC May Replace AC (2019)

#64

Post by dhdc »

distortedsignal wrote: post #61
elihu wrote: post #52

Earlier quoted context omitted.

He was running ten amps over thin wires; of course that doesn't work. The problem there was that he was transmitting significant power at low voltage and high current. That doesn't say anything about the superiority of AC or DC. AC has historically been the more practical choice because you can trade AC voltage for current easily with a transformer, but there are ways to do that with DC now too. Maybe there's an argu…

> 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]

Re: Why DC May Replace AC (2019)

#66

Post by dhdc »

zw123456 wrote: post #59

There 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…

Since we are doing DC-DC, I'd say we go with the highest DCV we can get away with. 12V is just simply too low and the associated I^2R losses will be unacceptable.

Re: Why DC May Replace AC (2019)

#67

Post by zw123456 »

dhdc wrote: post #66
zw123456 wrote: post #59

There 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…

Since we are doing DC-DC, I'd say we go with the highest DCV we can get away with. 12V is just simply too low and the associated I^2R losses will be unacceptable.

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.

Re: Why DC May Replace AC (2019)

#69

Post by dpierce9 »

zdragnar wrote: post #56
dpierce9 wrote: post #42

The major thing that is unaddressed is the inertia of the extant built environment. We know that lead paint is bad for people, especially kids, but we haven’t remediated it in much of the pre-1976 housing stock. Why? It is expensive and the places where it is worst are not high-value areas. Similarly, there are many homes in America with low voltage knob and tube which is an uninsulated wire. Would you retrofit homes…

It's a tangent, but worth pointing out that like asbestos, lead paint remediation is often more dangerous than doing nothing. Paint over it, and it isn't hurting anyone. Sand it off, and now you have super fine lead particles floating in the air and settling all over the place just waiting to be disturbed and kicked up again. Lead pipes are an entirely different matter, and remediation is usually (wrongly) deferred d…

Lead remediation isn’t just sanding and covering with paint is not always a good idea. First windows and doors are painted friction surfaces which create lead dust. Second, painting over it assumes the bond between the substrate and the lead paint will hold in perpetuity. In practice it doesn’t but yes often painting is a good form of remediation. This does not work outside though. Third, sanding is not great for all of the reasons you mentioned but not the only way to remediate (e.g., steaming, chemical stripping, physical encapsulation, or removal are all options). Fourth, it was really just an example of how the built environment is incredibly sticky to things which are downright dangerous, known to be dangerous, and yet continue to persist because of the associated expense. Your example is also good.

Re: Why DC May Replace AC (2019)

#70

Post by dhdc »

zw123456 wrote: post #67
dhdc wrote: post #66

Earlier quoted context omitted.

Since we are doing DC-DC, I'd say we go with the highest DCV we can get away with. 12V is just simply too low and the associated I^2R losses will be unacceptable.

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.

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