Ultra High Voltage DC Power Transmission.

This post was brought to you courtesy of the Central Propaganda Department of the Chinese Government.

So they plan to pollute the unique and pristine Gobi Desert. Wonderful.

And why are they opening so many coal-fired power stations and burning record amounts of coal?

They needn't do any of the above. They have some good designs for nuclear power stations, so they ought to be building them like fury. I know they're building some, but not nearly enough.

They are building anything and everything they can, but china is due for an epic financial crash that will wreck its economy for 50 years.

That's why they want to start a war.

So..... What I want to know is why DC, surely the problem of converting it all to AC has to have losses? DC fell out of favour back in the early days as you could not use transformers on DC. Brian

Hasn't this been discussed in this group fairly recently with reference to the links to France/Norway etc.?

Well that is an easy one. It's for the same reason that undersea (and long underground) links are DC, namely dielectric losses. These are of course much lower for transmission towers in air than for the substantial insulated cables required underground or undersea, but not negligible for long lines.

There's a point at which the capital cost (and losses) in converters is less than the AC losses.

Its not dielectric losses as much as a perfectly rotten power factor that means that there are huge out of phase currents, raising resistive losses to unacceptable levels. This is due to the capacitance to earth of a cable surrounded by salt water.

There is one further point, and that is synchronisation of grids. Very large grids spanning more than about 1000 miles start to run into time delay issues via the various parts that end up with large out of phase currents being drawn. DC interconnectors between segments avoid this problem.

Likewise if grids are not phase locked, some sort of AC-DC-AC coversion is necessary anyway.

Conversion efficiencies are pretty high really - very high 90s percentage wise.

Actually completely untrue. The gas shock is forcing all countries to re-examine their nuclear power programs, and there is a large voice calling for nuclear power across all of the world.

Long before undersea power cable were in use. the USSR was using Dc to cross from west to East.

Its a pity you didnt read the rest of what I wrote.

For same power transfer, DC also has lower (x 0.707) peak voltage of AC?

So, the pylons are cheaper to build?

Yes. But its not a huge issue. You size the voltage to the breakdown capabilities of your insulator and indeed your inverter semiconductors (or valves, whichever)...

I think the normal undersea runs at about 275KV. That's pretty high for semiconductors

For a 500MW cable that's still 2000A....

Much much cheaper. Cable uses the air for insulation, and to cool the cables .

Far far less capacitance to ground.

No need to dig holes in the ground to lay it.

No, I meant that DC pylons are cheaper than AC.

Apart from anything else, you don't need to transmit three phases, and keep those separated. So, whilst you might want several conductors, because those are easier to handle and rig, they can be in one bundle at the top of the tower.

Oh. Sorry. Not much in it really.

Well you don't *need* to 'transmit' three phases for AC either....

As maybe but we need the power now!, not in years time best to keep the old coal plants on the go for now I think lights out wouldn't go down well with the populace!....

Germany is not 'most countries' - it is the exception to the rule, because Germans are very very green and wet behind the ears. And will end up importing all their power from countries that are not.

Since when have nukes been considered 'green'

E.g. Belgium which is heavily nuclear is looking to SMRs to replace its massive nuclear fleet.

The reality is that in the EU with proportional representation and the greens as kingmakers, Nuclear has simply been off the agenda.,

But people are getting heartily sick of Greens and are increasingly leaving them on the side of the plate.

Oops yes. Long time since I did this stuff.

:-)

The EU, beginning to realise the stupidity of its total commitment to renewables, has now decided that natural gas and nuclear are 'green'!