[rescue] SGI Challenge L systems available in Denver

Francisco Javier Mesa-Martinez lefa at ucsc.edu
Fri Sep 17 15:20:43 CDT 2004

On Fri, 17 Sep 2004, Sandwich Maker wrote:

> yes yes yes...  i was assuming that since we were talking relative to
> specific loads we were talking about constant power.  [implicit in the
> statement 'you need thicker wires for running large loads' than with
> ac is the assumption that you'll be running at lower voltage, right?]

Huh?...  I was agreeing with the original poster on the load statement.

> " The reason for using AC is very simple: It is easier to genreate alternate
> " current, and AC can be easily stepped up or down. The low voltage/ hight
> " current generated can be stepped up to high voltage/low current for
> " transmission (lower loss when the current is smaller), and then it can be
> " stepped back to low voltage/high current at the destination point. Plus
> " you can also play with the phase in order to adapt for long distance
> " distribution, something that can not be done with DC.
> yes, westinghouse won because ac greatly simplifies the
> infrastructure, and tesla's invention of the alternator et al put his
> system over the top.
> but phase doesn't matter in dc - and the latest long-distance
> transmission lines are dc, because inductive and radiative losses
> losses are significant over hundreds of miles and hundreds of
> kilovolts.

That is correct, so basically AC is easier to generate, convert to DC for
transmission and then back to AC for distribution to the end user. Another
advantage of AC for domestic use is that the breakers for example are
"simpler" (i.e. cheaper), since DC arcs are much harder to interrupt. Also
DC currents used to be a pain to modify their voltages, but it seems that
a number of advances in the last decade or so has produced systems w/o the
necessity to go back and forth AC in order to modify DC voltages.

I think that recently high voltage DC has been used in some extremely long
transmission lines, not that much because of the inductive/radiactive losses
(which are not lower in DC than in AC for the most part as far as I would
guess) I assume that most of the losses in AC would be capacitative
though, correct? Also AC has issues over long distances when multiple
generators need to be in phase and so on, which I assume DC needs not worry

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