It wasn't my idea to start with you idiot, it was a discussion about possibilities. I'm so glad that a world leading expert such as yourself would chime in and share your dearth of knowledge. *snicker*
TDD
You sure "helped" it along.
It doesn't take a "world leading expert" to see that you're full of shit. Common sense is enough. Like I said earlier, try thinking for yourself sometime. Your neuron might be scared at first, but it'll calm down.
DC Power transmission lines are used to rid the line of skin effect and allow the entire cross section of the conductor to carry current. They are as yet only practical for long haul point to point circuits.
-- Tom Horne
That's what I read. My only experience with high voltage power transmission has been installing buried conduit, setting transformers, making connections and splices on 15kv coaxial underground cable. Of course there was all of the other wiring on the low voltage side of the transformer including the facilities wiring. What I find fascinating about the long haul high voltage DC power transmission systems has to do with the changes in technology over the years to handle the conversion of AC to DC then back again. The early mercury arc valve systems have got to be a sight to behold. I can imagine a mad scientist wearing super thick lensed glasses cackling in the background.
TDD
Its finally happened: USB
Which is why I suggested 100 insults ago that a 5vdc system might be usefully, and perhaps 12vdc
A more practical solution would be special J boxes that have the transformers in them and are sensitive to loads being plugged/ unplugged and cut off power to the primary when not in use. Everyone hates wall warts, they draw a little current even when not in use. Your electrician would then install these low voltage outlets easily throughout the house. The important thing is that they be able to detect "no load" and cut off the primary, and sense an item being plugged in or turned on and re-connect the transformer primary. Your whole house DC distribution idea would not be able to do this because it has to be "ready" globally with no local outlet control sensors.
picture...
There is no reason that could not be designed into wall-warts. I've never measured the quiescent primary current draw of old style wall-warts verses the newer tiny switcher wall-warts, I'm sure someone has done so. I think your idea is great for office cubicles because it could be built in during manufacturing and would help lead to a less cluttered work space, at least for some people.
TDD
Even a 5Kw 6 phase converter was a sight to see- looked like an octopus with glowing arms and a bright spot dancing on a dish of mercury. Seriously the advantages of DC transmission has relatively little to do with skin effect as conductors are typically ACSR with aluminum on the outside and steel inside- and, at these voltages are grouped in bundles. The size of the conductor has more to do with mechanical than electrical properties. DC transmission at high voltages is economical for long lines where the reduced cost of the line exceeds the added cost of the terminal equipment. There are also some other technical advantages . This breakeven point is at a much shorter distance for underground or underwater cable. DC back to back terminals are often used where frequency differences (e.g. in Japan with both 50 and 60 Hz systems) or stability concerns arise. They do have the disadvantage that reasonable and economic circuit breakers for DC don't exist and this means that the system is essentially point to point rather than through an interconnected grid. In addition, conversion from one voltage level to the next is bloody expensive, awkward and inefficient compared to the use of AC transformers. At low voltages, even for relatively short distances, DC is not a viable option.
From my reading, the problem of capacitive reactance is also minimized with the DC transmission lines. When I was at Kwajalein Missile Range during the late 80's, I got the chance to explore the old phased array radar installation on Meck Island. It had a room we called the Frankenstein room which was the power supply for the old radar. From what I was told, the way they were able to make that monster scan, was to change the phase angle of the microwave beam. The Frankenstein room looked just like a prop from a science fiction movie. I wish I still had the pictures. Here's a link, look for Meck Island an you can see the big building in the upper right. There are two pictures, one showing a view of the missile silo or silos. I don't remember if there were two.
Only the Navy with their ships and submarines make use of DC well. That still doesn't mean that it wasn't one hell of a costly implementation.
DC is great... on anything miniature, like a scooter, or model airplane. :-]
Supplying DC feeds that can push as much power as we are used to with current AC settings in the home would not be easy, and homes are low consumption examples.
Even if we had compromised, and made AC to the pole, and DC into the house, the DC part has a lot of pain in the ass required maintenance that AC does not suffer from. Galvanic effects being the first one I think of.
OK, so we drop the HV down to about 600V on the local poles, and then we rectify that and feed the homes? Sounds like a very high maintainence/service oriented method.
Maybe if we could make a nice DC chopper that would let us step off DC highs and Gnd lows.. kind of a psuedo-alternation.
Around 2002 I found a wonderful mid-sized mercury arc recifier in use still for the tram system at the MOTAT museum in Auckland, NZ - it might still be operational there. Fascinating to watch it run, and the brightness change according to load as the trams moved around.
I'm sure there are still some running in other countries, too, but that's the only one I've seen over the years (although various museums have ones that aren't hooked up - I don't know how many of those are still technically OK and could be made to run).
There may still be a few tucked away in buildings with really old DC elevators, although there can't be many left now that haven't been updated.
cheers
Jules
I do not think there have been DC elevators in the US since the late Thirties.
AlwaysWrong strikes again.
That too, and that is a major benefit. However, there is still a reactive problem at the receiving end where it is necessary to have the capacity to supply reactive. This will be dependent on load and the particular control of the system as a whole. For long lines this will be less than what would otherwise be needed to compensate for line capacitance.
o3p$i3r$ snipped-for-privacy@news.eternal-september.org...
Thats why Westinghouse beat Edison in the early days of deciding what electical distribution system to use, Westinghouse (scientist) wanted AC, Edison (who was more of an inventor than a scientist) would not let go of his prejudice for DC. I still have an old AC/DC radio from those days, when radios were sold to work on either distribution system.
Hmm, that triggered a memory. I used to have an AC/DC one from the '60s - manual switch, and you could feed 12V DC in on the same power socket as AC. I doubt something like that would pass H+S these days, never mind the amount of people who'd try to feed it domestic AC with the switch on the DC setting and fry the thing ;)
cheers
Jules
messagenews:habo3p$i3r$ snipped-for-privacy@news.eternal-september.org...
Have you had any experience with high frequency AC power systems? I've come across 400hz AC power in some old computer installations and seen a lot of military surplus aircraft power equipment that used 400hz AC power. My assumption has always been that higher the frequency, the smaller the mass of the transformers not only making equipment smaller but lighter.
TDD
Very common (standard?) in aircraft.
Filter capacitors and inductors too. It's not uncommon for switching power supplies to be above 1MHz, also to keep the size of components (and costs) small.
...and transformers get *very* big at DC.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.