From: ChuckKuecker (ckuecker@mcs.net)
Date: Fri Aug 21 1998 - 08:12:37 MDT
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At 04:09 AM 8/21/98 +0800, you wrote:
>If there was to be a new global standard for the "electricity grid",
>meaning the power outlets on the wall, which would be better, AC or
>DC?
>
>If you were creating new cities all over the world, and had it to do
>all over again, would you choose 120 VAC, 24 VDC, or something else?
>
>In terms of eliminating the needs for transformers, adapters,
>converters, etc., what would be the most efficient standard?
>
An AC standard makes most semse for a distribution system. In the
future, the present copper webworks may not exist, and be replaced
with small generators or fuel cells at the point of use. Here in
Illinois, Commonwealth Edison is planning on selling small natural-
gas powered turbogenerators to consumers who then make their own
power, free of the grid. The generators will produce 60 Hz AC because
all our systems expect it now.
For machinery, 3-phase AC is king, as the induction motor requires
it, sepecially in the larger horsepower ranges. Advances in power
inverters may make this obsolete, as the required AC can be created
from DC if needed.
AC has one big advantage over DC - the voltage can be simply raised
and lowered with transformers to allow transmission of power over
long distances. There have been a (very) few high voltage DC
transmission lines - the one I remember most is a coaxial cable from
England to France that transfers power from whoever has the surplus
to who needs it. There's a bidirectional HV inverter on each end of
the cable to connect to that countries' AC grid.
If fuel cells or some breakthrough in home nuclear power becomes
popular, the generator will probably produce DC. In this case, a
local inverter can make AC for motors, etc. Lighting can work as
efficiently from either DC or AC.
A 24 V DC system would be OK for small loads, but you need heavy
wires to conduct the current required for big loads, one reason that
440 V 3-phase is so popular in industry - the wiring is much cheaper
than if a lower voltage was used.
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