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Mainly, line loss (voltage drop) as the lines get farther from the
generator. In order to have nominal voltage near the end of the line, the
generator voltage had to be somewhat higher. Although proper engineering can
accommodate some voltage variation, early electrical devices lacked
sophistication. So, some devices overheated.
In addition, wiring techniques varied all over the map in the early days; so,
much of the problem may have been mechanical and cured by the rapid
proliferation of electrification with the development of AC.
Vis-a-vis the question of magnetic fields, DC magnetic fields are more or
less stable, while AC fields build and collapse in opposite directions 60
times per second. Some "authorities" claim it is the variation in the field
that is dangerous. While the jury is still out, the only serious research I
know of that links magnetic fields and disease is for doubling of a certain
rare brain cancer in electrical workers exposed to extremely high-intensity
alternating magnetic fields.
BTW, modern ultra-high-voltage transmission lines are DC because it suffers
less line loss than AC at these voltages.
John -dot- Renish -at- conner -dot- com
My statements are my own and do not represent Conner Peripherals, Inc.
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