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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
>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 naturalgas 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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