Researching the history/compatibility of 120v DC/AC utility power

Wendy

Joined Mar 24, 2008
23,473
I can live with that, but given superconductors of this type are currently a fantasy the problem is not coming up too soon.

Of course, we could always use impedance matching and coax to minimize losses. In any case, the voltage would still boosted, since superconductors are also current sensitive. The voltages may even be much higher values than currently used.
 

WBahn

Joined Mar 31, 2012
30,286
The superconductors themselves are not really the problem. Even 20+ years ago when I was working in the superconductor research group at NIST, wire fabrication technologies for conventional superconductors were quite mature. We would routinely push 4000A (because that was the limit of our capability) through conductors the size of a mechanical pencil lead in 10+ Tesla magnetic fields. In ambient fields, those same conductors would probably have carried tens of thousands of amps before going normal.

But to use them in practice, you also have to have the cryogenic support. For standalone installations, such as an MRI machine, this is no big deal. Liquid helium is expensive, but once the magnet is cooled, the parasitic burn rate is pretty manageable. But providing uninterrupted cryogen support for distribution is a whole other critter. Not only is it technically challenging, but it's not cheap to build nor free to operate. Those expenses have to be weighed against the present transmission losses and I don't know that the scale will ever tip in the favor of superconductors.
 

Thread Starter

DMahalko

Joined Oct 5, 2008
189
The only bias here is trying to discuss a topic that is not well understood or explored anymore. I keep focusing on DC because, um, that is the topic of the thread. That's what thread topics are supposed to be about?

The primary knowledge is in books 75+ years old at this point, back when doing anything moderately powerful required a metal forge to cast parts weighing a couple tons.

This might be a challenge to build now:


Figure 328: A large current low voltage bipolar dynamo built for electrolytic work and here shown to illustrate the large size commutator and brushes necessary to collect the large current.

  • The machine here illustrated gives 310 amperes at 7 volts when running at a speed of 1400 RPM, corresponding to an output of 2.17 kilowatts.
Yep, I scanned and uploaded that from a 1917 book set I bought for $100 on ebay, which is in the public domain in the United States, and so all the content can be reused on Wikipedia:
Hawkins Electrical Guide



The discussion of a DC/DC high voltage transmission grid is theoretical and would not qualify for a Wikipedia article because it does not currently exist in any form, and primary sources such as scientific journals and studies generally don't qualify as a usable source. Secondary sourcing is usually required where someone else has distilled the topic.

I am simply proposing concepts in order to explore how it could work or be utilized. It is almost certain that a bidirectional solid state DC/DC step-up/step-down SMPS converter has never been built or even contemplated before. Bidirectional cable antenna amplifiers also likely never existed in the cable TV industry, before the concept of cable modems were contemplated.

There are fun and really technical questions here that probably have no known answer -- anymore. So if 125v DC is "harder" to break arc than AC, does this mean that a 125v DC circuit breaker will by default work fine with 125v RMS AC?



I am aware of Mike Holt. There can be an intellectual bent to learning the NEC and other building codes, though it's more about "How did this person violate the code rules" or "what are the specific rules differences for the 2005 vs the 2008 vs the 2011 if you have to work in different jurisdictions". There's lots of facts and figures and tables to memorize too if you want, but it's a very narrow straight down view at just what you need to know to do your job and pass the certification tests.



Also, didn't you know, DC is a bias'd topic to begin with. :p
 

#12

Joined Nov 30, 2010
18,224
Personally, I prefer stepping up the frequency of the power grid. That would make all the transformers and motors smaller. (400 Hz is used in some aircraft.) Imagine a 3HP drill that you can hold in one hand!

We could also consider 440 Hz. We could still use the power line frequency to keep our clocks accurate, and we could tune our guitars with it.
 

#12

Joined Nov 30, 2010
18,224
True. I have already seen one person that was too dense to let go of the drill before it ripped the tendons in his arm, and that was only a 60Hz drill.
 

takao21203

Joined Apr 28, 2012
3,702
Not to forget DC needs polarized plugs, and if you look all these different DC wall adapter plug sizes + 2 different polarities you see how stupid people are, and that very likely this will never work out properly.

So, rip out the existing wiring from all buildings?

We have so many old buildings in cities which are totally a waste in terms of heating and space efficiency, but we keep them.

Also see this: http://forums.energymatters.com.au/energy-efficiency/

There might be more people over there with advice for your DC grid questions.

You may find your research already has been done elsewhere.
 

takao21203

Joined Apr 28, 2012
3,702
The high voltages are commutated with phase link thyristor banks.

Or how can a DC generator for 300 kV become isolated?

Have you seen generator bars some time?

What you write, that nobody is on the grid, is cery unlikely.
So you also can't switch High voltage D.C. properly.

Not under load, that is...
 

Wendy

Joined Mar 24, 2008
23,473
With the advent of 3 prong grounded plugs DC would not be a major reach. I suspect a lot of the same safety standards could translate over (including ground), though the plug should be a lot different to prevent confusion.

Since appliances in general are not going to be able to use DC, there is no reason use 120VDC as a standard. I think this is what is bothering a lot of people. Trying to convert to a new system while keeping old conventions in place simple does not make sense.

120VDC would be very dangerous, with no real benefits. How about a 36V, or a 48V system at the house? You are already talking about dropping line voltages with DC/DC converters. You could make it a safe system just as easily.
 
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