"Dwight K. Elvey" wrote:
> I'm not sure if they had the same reason but today,
> DC is actually used for long range, high voltage lines
> in a number of places. DC doesn't require the insulation
> to hold off quite as much voltage. It doesn't suffer
> from inductive losses.
But you need specialized devices not available at the end of the
19th century to produce DC in the required range (>750KV).
Back then you only had the transformer (or inefficient DC-DC
motor converters(.
> It isn't much good for home use. In fact, lamps don't
> do as well on DC as AC because of the electrical effects
> of the wire evaporating ( not sure which end goes first ).
Ah, the "Edison Effect". Some electrons (especially those
closer to the negative side) would jump away from the filament
and then, thanks to the electric field, land on the filament
but closer to the anode. The result was that the section of the
filament closer to the anode would be carrying more current
than say, the first third of the length of the filament (in the
- towards + direction). So filament failures almost always
occured in the last 1/3 of the filament. The fact that part
of the current traveled through the space, not the filament,
was extraordinary news in 1883, especially since the electron
was unknown at the time.
With metal filaments this became worse since some metal atoms would
migrate closer to the - terminal.
carlos.
--
Carlos E. Murillo-Sanchez
Dean of Engineering
Universidad Autonoma de Manizales, Manizales, Colombia
----
"After finding no qualified candidates for the position of principal, the
school department is extremely pleased to announce the appointment of David
Steele to the post." Philip Streifer, superintendent of schools, Barrington
RI.
Received on Mon Dec 13 2004 - 12:00:03 GMT