DC ring main around the earth

[bruce varley]

I heard this suggestion a long time ago, not sure where. It's pretty extreme
and there are lots of factors against it, but this is one forum which should
at least consider it.

The idea is to run a BIG DC ring main around the earth, traversing many
equatorial parts where the solar energy (and in some places wind) is
moderately reliable. That way you can have relatively constant energisation
through renewable sources. Spurs running north and south would feed the
energy to consumers.

 

[Bill Shymanski]

Ohhh! Ohhh! Can we get the engineering for that? Let's see, 10% of 5
trillion would be a very nice addition to the company bottom line - even
if it was spread out over 25 years or 50 years.

Aside from the ruinous high cost of consulting engineers to design the
thing, practical problems with this would include:

1. High voltage DC circuit breakers are still pretty much a research
topic, and not something you can order from a catalog. This means that
right now it's impossible to tap a HVDC line - multipoint distribution
is not practical without some way to protect the branches.

2. There's probably an upper physical limit on the DC voltage you could
use, in terms of how much corona loss you can stand per km for conductor
bundles of a practical size. I suspect the limit is well under 2
million volts pole-to-pole. This severely limits the transmission
distance - I doubt a line even 10,000 km is practical.

Right now this part of the world is looking at a much less ambitious
connection to take advantage of the fact that when it's supper hour in
Ontario, the kids are just getting out of school in Alberta - thereby
spreading out the peak loads, and also allowing Manitoba to sell hydro
power in both directions. Not 5 trillion, but I'm sure 5 billion
dollars would get used pretty quickly.

Bill

 

[John Gilmer]

1. High voltage DC circuit breakers are still pretty much a research
topic, and not something you can order from a catalog. This means that
right now it's impossible to tap a HVDC line - multipoint distribution
is not practical without some way to protect the branches.

Come on: the "taps" would be just like the terminals. They would be you
"basic" (and expensive) DC-AC bi-directional conversion stations.

2. There's probably an upper physical limit on the DC voltage you could
use, in terms of how much corona loss you can stand per km for conductor
bundles of a practical size. I suspect the limit is well under 2
million volts pole-to-pole. This severely limits the transmission
distance - I doubt a line even 10,000 km is practical.

Over land it would be just like the situation today with AC networks: Power
is "wheeled" from end to end rather than sent along a un-tapped transmission
line. For the necesssary underwater links, the present technology just
isn't up to the problem.

Right now this part of the world is looking at a much less ambitious
connection to take advantage of the fact that when it's supper hour in
Ontario, the kids are just getting out of school in Alberta - thereby
spreading out the peak loads, and also allowing Manitoba to sell hydro
power in both directions. Not 5 trillion, but I'm sure 5 billion
dollars would get used pretty quickly.

Amen. The intra-continental links are not yet fully developed (or
"debuged".)

 

[Don Kelly]

Come on: the "taps" would be just like the terminals. They would be you
"basic" (and expensive) DC-AC bi-directional conversion stations.

---------------
This can be done-in theory- it is expensive and each such tap requires both
a rectifier and inverter as well as AC reactive sources. That is each would
be a "back to back station" If you wanted feeder spurs to be DC then the
equivalent of 3 AC circuit breakers would require the equivalent of 3
converter stations. as well as the availability of a strong AC system at
each tap point. At some point "feasibility" degenerates into a no go
situation. This point is reached long before consideration of a "round the
world link".>In the case of a cross-continent tie -the tap points would be
reduced to back to back converters such as those in Japan,
Alberta/Saskatchewan and Eel River New Brunswick (all of which are DC for
stability or frequency conversion needs ). At these "taps" the local
systems do need some muscle.

Over land it would be just like the situation today with AC networks: Power
is "wheeled" from end to end rather than sent along a un-tapped transmission
line. For the necesssary underwater links, the present technology just
isn't up to the problem.

Again, in present AC systems, circuit breakers at reasonable cost and
effectiveness are very important. How far apart must the 'taps" be to make
it either economically or technically worth while to use such a tapped DC
system? (yes- there is in fact such a system if I remember correctly- the NW
power pool DC link which ties strong areas of generation to major loads and
is in parallel with AC ties

It all boils down to the merits and demerits of any proposed situation: Load
here---Generation here---what's the best way to get them married? In some
cases, don't bother- intercontinental transfer may have no net benefits and
a lot of costs even if technology was up to the task.

Don Kelly
[email protected]
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