Gene Smar wrote:
> TT:
>
>
> ----- Original Message ----- From: "jimlux" <jimlux@earthlink.net>
> To: "K1TTT" <K1TTT@ARRL.NET>
> Cc: "'towertalk reflector'" <towertalk@contesting.com>
> Sent: Friday, September 04, 2009 10:23 AM
> Subject: Re: [TowerTalk] Static Discharge Wicks
>
>
>>
>> What radius? you'd have to look at the fields.. but let's say the field
>> is 10kV/meter under the thunderstorm. You have a 20 meter high tower,
>> so the potential of "the air" at 20 meters, if the tower weren't there,
>> would be about 200kV. If the tower didn't perturb the field (which it
>> does, but that just helps, here).. the grounded antenna would be at that
>> potential relative to the surroundings. The radius of curvature needed
>> to prevent breakdown at 200kV is on the order of 3" (6" diameter) which
>> is pretty big.
>>
>
> It is for this same reason (high field intensity surrounding a small
> energized conductor) that power transmission lines operating at 500 kV
> and up use two conductors per phase. You can see the paralleled wires
> suspended from twin sets of insulators at each end of a span and
> jumpered together along the span with shorting bars. To operate the
> lines as single conductors would only cause arcing and concommitant
> energy loss along the entire line. The dual conductors spread out the
> E-field that surrounds the phase, keeping the field from getting too
> high and arcing over in air. (The two conductors are NOT needed to
> carry the current.)
>
> Just thought you'd want to know.
>
>
also reduces inductance (very slightly, but on 1000 km of cable, it adds up)
and reduces resistance (skin effect) (skin depth at 60Hz in aluminum is
something like 1/2" or 1/4", but again, 1000km of cable, etc.)
You also see triples and quads (although the +/-500kV DC line around
here only uses pairs)
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