Huh? I thought it was generally accepted now that DC is better for very long transmission lines.

If they use AC, how are they going to handle the phase issue?..zero degrees in Minneapolis and zero degrees at some other load city are not going to be at the same time.

david,

The whole grid is supposed to be synchronous. But generators drift. Which is why that around midnight every day the grid is shifted +/- to account for phase drifts. There is still the problem (as you point out) of small phase shifts causing circulating currents. If transmission lines had zero resistance these phantom currents would not matter much (except for sizing of eqpt). However, since our lines have finite resistance phase currents contribute to unbillable losses.

DC has been recognized as best for the long distances for decades. I remember details from around 1960.

But I haven't studied why adoption has been so slow. Probably because our power companies are regional and their investments and innovations are regulated.

And constructors and manufacturers will keep making what the buyer wants.

How will they handle the intermittency problem? The German company ION, which a substantial number of wind turbine generators, says the transmission net becomes unstable when wind power becomes a significant fraction of the total generating capacity.

Bob,

That is part of the beauty of DC. Instability problems are greatly reduced.

In any case wind has to get up to 10% before there are problems. It is currently at 1% or so. There is a ways to go.

DC transmission? The whole reason AC won out over DC back when electricity was being introduced was due to the inefficiency of DC transmission - the losses are simply too great to transmit any great distance. AC, but not DC, can be transformed "hence the term "transformer") up to very high voltages/low amperages to allow long distance tranmission. If someone has a method to use DC for distance transmission, it would still need to be transformed (using a DC motor to generate an AC current, with attendant losses) near the point of use, since every house and business in the country is wired for AC. If someone can point to a link describing this proposed DC system, I'd love to see it.

alanstorm: No, I don't think you want to see at all.

If you did want to see you would have gone to Wikipedia HVDC and found many links to specific places it is in large-scale use. You would also find that solid-state devices developed in the last few decades were needed to create the modern HVDC.

Wikipedia has a thorough discussion of the merits and problems. A great problem is that HVDC systems, or any DC, is not well suited to short distance transmission. There is zero chance that DC will be used for local power. The whole point is to move power long distances.

The DC of Edison is totally different from anything in use today. Forget DC motors.

"alanstorm: No, I don't think you want to see at all.

If you did want to see you would have gone to Wikipedia HVDC..."

Annoymous, you are an ass. What would make you make such a statement, other than your own inflated sense of adequacy? My statement about wanting to see something on the subject was EXACTLY THAT - no more and no less. (BTW, the article was indeed informative - I had no idea of the developments in the field.)

That, however, does not excuse your incredibly rude and condescending tone.

I took a two-day drive through the SoDak/South Minn. wind farm last construction season. There was a lot of activity, especially road closures for transit of v.large tower tubes that had come, a local said, up the Miss. on barges.

The towers are in clusters of 3-7. For every group of three, one was out of service. Now I am not an EE, but that seemed excessive. Maybe Mpls/St Paul was full up with juice that week? Perhaps Anon can insult me, and send a link explaining that.

Because it sure looked like Amateur Night at Tomorrowland from where I stood, hot shot.

alan,

Your understanding of DC vs AC is about 100 years behind the times. And the use of MG type converters is rather out of fashion given 6,500 volt 600 A IGBTs.

http://www.pwrx.com/Grids.aspx?g=128&m=50

DC to AC conversion in fact is rather practical even at lower powers and is one of the elements in the advent of the variable speed AC drives now becoming common.

What the immediate future holds (10 to 20 years) is HV DC for long distance transport and AC for local distribution.

Anonymous says that there is "zero chance that DC will be used for local power" but I thought that some contractors were using Power over Ethernet wiring to power low-voltage lighting throughout a house. Also, many appliances require AC to DC conversion to run (cell phone chargers, computers, etc.). Except for the big motors (Refrigerator compressors, washer/dryers etc.) couldn't a house run on DC?

M. Simon: Yes, it is possible to operate a house on DC. But I think zero comes close to the probability that our standard will be changed to DC.

However if such came about the problems that plagued Edison DC can be overcome. His system worked, it just lost to a better one.

It would help a lot if all the small DC devices used the same voltage and plugs were standardized at the device end. But power consumption varies so one plug size seems impractical.

I wouldn't run Power through Ethernet but you could, it is wire. The question might be "why?" Standard low voltage DC wiring is not rare. It is usually used only for built-in lights, around swimming pools, and lawn lights. I would use that wiring standard rather than Ethernet.

We go off topic in discussing the local electrical supply or house wiring. HVDC is beast suited to a different problem.

alanstorm: At the risk of getting trashed I will guess what irritated Anonymous.

There is a rhetorical trick more familiarly called a Wild Goose Chase. The trick is to give someone a task that cannot be done. And impossibility.

There is no proposed DC system. This large project will use AC and the question is why not use DC?

So when you asked for a link to the proposed DC system you asked for the impossible. It would have been a Wild Goose Chase looking for what doesn't exist.

It is fine to be uninformed about HVDC. The great portion of mankind is and always will be. But it is amazing that you didn't realize from the posting and the previous comments that HVDC is very real. And then reading only a few minutes online would have given you the background information.

Instead you issued what can be taken as a challenge "I'd love to see it."

People can't hear your tone of voice online.

Actually, with new designs coming on line it is now economical to do utility scale DC to AC conversion with loads as small as 30 MW.

And yes - in theory your house could run on DC. The problem is cost not technological ability.

I think the Space Station runs on DC - a 270 VDC bus IIRC. So maybe the house of the future is DC already.

It would help a lot if all the small DC devices used the same voltage

It is worse on the other end of the plug. I'm designing a microprocessor system that has at least six different DC voltages at this time and may wind up with 8 or 12 before it is done.

M.Simon: Sorry, I should have sent my 5.52PM house message as a reply to Some Fool who commented just after you at 4.18PM. Name error.

I don't quite grasp the meaning in your first sentence. But it sounds like progress. I'm for that.

What is 'utility scale?'

I'm guessing it means a solid state converter station for DC to AC can now be afforded at a modest local level, 30MW.

That serves, what, 6000 homes? A town.

I think the "average home" averages 3 KW so 30 MW = 10,000 homes.

Utility scale power is in the MWs. Home scale is in the KWs (or less).