Comment: DC power is great once you

(See in situ)


DC power is great once you

DC power is great once you have high-efficiency semiconductors to do voltage conversion for transmission.

If you are using rotating machinery you have very low voltage limits - far too low for long-distance transmission - because commutators arc over. Back in those days, AC and transformers beat the pants off DC and rotating machinery, transmission-efficiency wise.

DC was approaching competitive breakeven for long distance transmission about the start of the '60s. But by then so much installed plant was AC that it also had to convert back to AC at the terminal end. So very few DC long-distance transmission lines have been built. (It's gotten a LOT easier in just the last few years, thanks to Moore's Law. So you may see a few more, or even some conversions of older AC systems.)

To justify replacing in-place infrastructure you need to have, not just an advantage, but a BIG advantage. Like a factor of 10. AC is good enough that a factor of 10 isn't available.

Also: DC has some disadvantages. A big one is a safety issue: It's a lot harder to extinguish an arc with DC than AC, so you need better circuit breakers. It also has a greater risk of locking-up your muscles if you grab onto it at home-power voltages, and you'd need to rewire with more than twice as much (expensive!) copper to run your house distribution at 48V nominal. (It also makes trees bend if you don't swap the polarity occasionally.)

Now if we get a practical fusion reactor of a polywell style (or another that can do P + B11 -> 3 He4) which can direct-convert the fusion energy to DC by electrostatic deceleration of fusion products, you'll get the output as DC at about twice the voltage of the current DC transmission lines (which could be handled very easily by existing DC transmission technology with larger semiconductor and insulator stacks, slightly taller poles, and fatter hollow wires). This might drive the installation of new DC transmission long-lines operating at the natural voltage of the fusion products of this reaction, allowing reactors to be hooked directly to (the positive side of) the high lines without voltage conversion equipment, cutting long-line terminating equipment costs by maybe 20%.

= = = =
"Obama’s Economists: ‘Stimulus’ Has Cost $278,000 per Job."

That means: For each job "created or saved" about five were destroyed.