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I apologize for making one of those horrible mistakes that seem to occur at
3AM.
For the 100 horsepower motor to run at 50 percent efficiency at a distance of
1/2 mile from the source, the wire cross section area is 0.4 square inches and
the conductor pair's weight is 3 pounds per foot for a total of 7,800 pounds,
contrary to my earlier erroneous calculations.
Losing one-half of the generated power in the process of connecting to the
load one-half mile away seems unreasonable. Increasing the size of the
current-carrying wire is a possible remedy. For our example, to enable the
motor to run at its full 100 horsepower with 90 percent efficiency, the supply
voltage must be raised to 110 volts and the weight of the copper conductors
becomes 75,000 pounds total. That is an unreasonable remedy. It is Edison's
problem and was never solved to anybody's satisfaction. That's why nobody uses
low voltage DC except (for example) in cars where there is a battery within a
few feet of the starter motor.
--rod
(As an aside, when Detroit changed the automobile system from 6 volts to
today's 12 volts, they cut the weight of copper wire in the car by a factor of
4.)
On Oct 9, 2011, at 3:22 AM, Rod Holt wrote:
> Certainly Jobs was no Edison, for which we can be thankful.
> Smil's Edison is mostly hocum.
>
> This article is absurd, not because it belittles Jobs, but rather that it
> attributes the success of all things electrical to Edison. Smil states:
> But the electric system remains Edison’s grandest achievement: an affordable
> and reliably available supply of electricity has opened doors to everything
> electrical, to all great second-order innovations ranging from gradually more
> efficient lighting to fast trains, from medical diagnostic devices to
> refrigerators, from massive electrochemical industries to tiny computers
> governed by microchips.
> This is an unfathomable exaggeration. It is like awarding the invention of
> quantum theory to the Greek Atomists like Democritus (5th Century, BC).
>
> Edison’s electrical system was all DC (direct current) and was quickly
> recognized as a dead end because the voltage where power was delivered could
> be changed only by motor-generators, which were grand pieces of whirling
> machinery but terribly inefficient, expensive, and required continuous
> maintenance.
> For household lighting, Edison supplied 100 volts. But for example, to run a
> 100 horsepower motor at that voltage located just one-half mile from the
> power source (say a steam engine-driven DC generator) required a pair of
> copper wires 13 square inches in cross section and totaling 250,000 pounds of
> copper! To avoid this, power was distributed at 600 volts or higher so the
> copper needed was reduced to 7,000 lbs, still an enormous number. And even at
> that, half the generated power was lost between the generator and the motor.
> With Edison’s system, the user had to be physically close to the source.
> Otherwise intermediate motors had to be built which ran from high voltages
> and in turn ran generators producing useable low voltages.
>
> Westinghouse and Tesla very quickly made a fool of Edison by generating and
> distributing alternating current (AC) where voltages could be increased or
> decreased with transformers requiring no moving parts, no maintenance and
> were easy to build. The distribution system envisioned by Tesla and
> Westinghouse is that in use today.
>
> If Smil’s deifying Edison wasn’t enough to sicken you, then see how he
> complains, “Until 2010, none of the microprocessors in Apple’s i-products
> were designed or made by Apple.” Imagine that. A sharp observation by Smil,
> indeed. I’ve made similar observations. Some years ago I noticed that Frank
> Lloyd Wright didn’t make re-bar, nor nails, nor concrete, and naturally I
> wondered how he had become so famous. I have not yet figured it out.
> But I have figured out the origins of Vaclav Smil. He is a scholar with the
> American Enterprise Institute, a co-fellow with John Bolton, Lynne Cheney,
> Wolfowitz, Gringrich, Richard Perle and other deep thinkers well known for
> their honesty.
> If I were Steve Job’s ghost, I’d smile.
> --rod
>
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