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# [Phys-L] Re: long-distance electric power transmission

• From: "Frohne, Vickie" <VFrohne@BEN.EDU>
• Date: Tue, 22 Mar 2005 09:21:33 -0600

Why not choose larger values? Because the line voltage is limited by=
the insulators and the breakdown of air. When the electric field be=
comes around 30,000 V/m, the air ionizes. To put it simply, the elect=
rons and the positive nuclei in the atoms are pulled in opposite dire=
ctions in the electric field. If the field is strong enough, the out=
er electrons pop right off - hence, ionization. Ionized air conducts=
electricity, and the result is a large spark. In that case, the ele=
ctricity doesn't get where it's supposed to go.

As for AC vs. DC, I did not know that some power transmission is DC, =
so let me speculate.... The advantage to AC is that transformers can=
be used to convert high voltage/low current to low voltage/high curr=
ent and vice versa. One advantage to DC might be that DC power lines=
uld cause energy loss for AC lines. However, the electricity must be=
converted back into AC at some point in order for transformers to wo=
rk.

=2E.......... I looked on Google, too. Yep, DC transmisison is used =
when capacitative coupling resulting in energy loss (the radio antenn=
a idea) is an issue. DC is also used when there's a problem in gettin=
g power stations in phase. See