When I was looking for a picture of a HVDC power line I stumbled on a report about DC distribution in buildings.

It's from the Swedish institute "Elforsk" ("El" means electricity and "forsk[ning]" research. You can figure out the rest)

Anyway, the idea put forward was a 350 VDC network to replace existing 230 VAC. In 33 pages they conclude that it would work but cost a lot of money. (This was intendend for a residential area where construction just finished here in Stockholm. The report is a few years old.)

Apparently, there were earlier ideas about a 400 Hz network in another residential area. (Never built)

I learnt something else: Submarines have standard 220V and 440V 3-ph 60 Hz systems.

I will provide the link, but there isn't even an abstract in English. Sorry!

Link

[This message has been edited by C-H (edited 01-09-2006).]

The Royal Dutch airforce has been using 400 Hz for years. ( used in other European countries too )
Main reason is that plant is more efficient and more compact.
We used 115Vac @ 400Hz for power and 416 Vac @ 400 Hz for 3 Ø machines.
Cheers Ray

AFAIK, 400Hz is standard all over the place in the military. Makes for lighter gear.

Yep, virtually all Air Force aircraft use 115v, 400cy 3ph AC.

And it hurts a lot when you get bit!

To a degree, this is why the Switch-mode Power supply has won out over the Linear type.
With a higher frequency, there is less transformer.
However, DC, within buildings, is a totally different kettle of fish.
Most places are designed to have AC switching in them, the difference being the distance between the contacts and the speed at which they close (or more importantly) open.
AC has a natural current zero, twice per cycle.
DC has none of this.
I have heard of where a bulb has blown, that the arc has travelled back down the wiring to the switch and had the switch not been opened, the wiring coulkd have burned further.
DC needs a lot heavier contacts and quicker opening than AC.

I've seen 400Hz systems on some of the ferries as well. Smaller transformers etc. would certainly be an advantage for distribution at that frequency.

Why 350V DC though? Are they actually suggesting that this could become a standard utilization voltage in domestic systems?

It seems that would necessitate a complete new range of appliances for domestic use, not to mention making simple brushless induction motors in small appliances impossible to use.

My guess is to allow the use of exisiting switchmode power supplies which already run on around 340VDC (rectified & filtered 240VAC).
It's a stupid idea though, apart from the switch issue (are we going to see a return to tumbler switches?). Are we going to have two light bulb sections in the supermarkets? One for 350V and the other for 230V? Think of how long the 350V bulbs are going to last in areas with conventional 230/240v mains!
What of the insulation requirements too? I have a set of British electrical engineering books printed in 1931. Apparently the reason for 250V being the highest voltage for domestic consumption was because the fire authorities felt that anything higher would compromise the insulation available at the time.
Someone must have a lot of idle time to think up strange new supply voltages and frequencies...we've been through all that over the last hundred years.

Aussie240 found the reason for the voltage.

They did make a list of all common (and not so common) types of equipment and appliances only to find that none will work. This wasn't enough to deter them. The authors believe that going from 230VAC to 350VDC will be easier than from 230VAC to 230VDC simply because more and more equipment contain switch mode power supplies.

About the only thing they found to be tested for this use were wires and fuses.

The peak value of the sine wave of 230 - 240 - 250 volts supply is.
324V - 338V - 352V. ( could be a reason why that voltage level was chosen )

Standard 230 V. mains cables are dc tested at 500 Vdc with a megger anyway.

The other things with rectified ac makes sense. 230 x 1.41 = 324 V in case of switch mode powersupplies.

I don't think dc is a good option at all.

To make and especially break a dc load need special heavy duty switchgear, because the arc doesn't extinguish 100 times a second as with ac.

A standard lightswitch wouldn't last long at all.

It's always an interesting topic to discuss these alternative options.

Chhers Ray.

I sometimes wonder whether it is (or better will be) ecologically (regarding over all power consumption) useful to provide for example 24 VDC on the base of a flat or house as a separate cabling. More or less all electronic devices could work with a primary DC source as well.

But to run a hoover or a washing machine or an elevator on DC does not really persuade me at the moment.

Wolfgang

There's no real advantage to it outside of some very specialist applications. 50 or 60Hz systems are quite satisfactor for almost all applications.

There would be no logic to change to 350V DC!

Ah.... I don't know why the peak value of 240V RMS didn't occur to me before. It kind of makes sense, in a way.

I don't think it would be a very sensible move though. What about all the millions of appliances already in use which rely on a transformer or induction motor? That's not to mention everything which has been designed for A.C. only in the last few decades and has switches which would not last long on D.C.

It seems to me that this would just be introducing another standard for no good reason.

@Wolfgang: Voltage drop would be a big issue with 24V. I know a guy who runs his house on solar panels only, and he wired his 24V ceiling lights with 6mm2 - that's ridiculous. Besides, most small appliancess use all kinds of queer voltages inside, so they'd need a DC-DC converter like a chopper anyway. So I think a Switching mode power supply or good old transformer from 230 to whatever voltage is needed is still the better option.