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From: jamm on 16 Feb 2010 17:14

Something i've never puzzled out..

If I make a 14kv generator (and I have made a few high voltage generators in
my time), I get constant corona from its unattached output.

Why do the 14kv power lines strung around town not do the same? I know
sometimes there is just a little bit of discharge around power lines, i've
seen and heard it. But thats not what i'm talking about.

Is it because the lines are fully terminated into a load?

--
*From the 1966 TV series:*
Robin: You can't get away from Batman that easy!
Batman: Easily.
Robin: Easily.
Batman: Good grammar is essential, Robin.
From: Bob Eld on 16 Feb 2010 17:49

"jamm" <joe(a)friend.com> wrote in message news:4b7b1883(a)news.acsalaska.net...
>
> Something i've never puzzled out..
>
> If I make a 14kv generator (and I have made a few high voltage generators
in
> my time), I get constant corona from its unattached output.
>
> Why do the 14kv power lines strung around town not do the same? I know
> sometimes there is just a little bit of discharge around power lines, i've
> seen and heard it. But thats not what i'm talking about.
>
> Is it because the lines are fully terminated into a load?
>

No, It has nothing to do with the load. It has to do with the electric field
intensity. The field lines converge into conductor. The smaller the radius
of that conductor, the higher the field strength is, because of this
convergence. The lines get closer and closer together as they converge.
Depending on air pressure, humidity and other factors break down of the air
causing corona happens at a field strength of about a million volts per
meter. That number is easily exceeded with small diameter wires or point
sources whereas the power lines are much larger in diameter and never
terminate in points that could cause such breakdown. Your bench top supplies
have small wires with sharp ends that create the high field intensities.
Note that very high voltage lines are always multiple conductors spaced a
number inches apart for this very reason. It keeps the converging and
increasing electric field in check within allowable limits around such
lines. There are equations to determine the expected field intensity around
a given conductor.


From: John Larkin on 16 Feb 2010 21:14
On Tue, 16 Feb 2010 13:14:51 -0900, jamm <joe(a)friend.com> wrote:

>
>Something i've never puzzled out..
>
>If I make a 14kv generator (and I have made a few high voltage generators in
>my time), I get constant corona from its unattached output.
>
>Why do the 14kv power lines strung around town not do the same? I know
>sometimes there is just a little bit of discharge around power lines, i've
>seen and heard it. But thats not what i'm talking about.
>
>Is it because the lines are fully terminated into a load?

HV lines do have corona loss. As noted, big conductors and
large-radius hardware helps.

Termination doesn't matter, just voltage gradient.

John

From: terryS on 17 Feb 2010 15:47
On Feb 16, 11:14 pm, John Larkin
<jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> On Tue, 16 Feb 2010 13:14:51 -0900, jamm <j...(a)friend.com> wrote:
>
> >Something i've never puzzled out..
>
> >If I make a 14kv generator (and I have made a few high voltage generators in
> >my time), I get constant corona from its unattached output.
>
> >Why do the 14kv power lines strung around town not do the same? I know
> >sometimes there is just a little bit of discharge around power lines, i've
> >seen and heard it. But thats not what i'm talking about.
>
> >Is it because the lines are fully terminated into a load?
>
> HV lines do have corona loss. As noted, big conductors and
> large-radius hardware helps.
>
> Termination doesn't matter, just voltage gradient.
>
> John

Function of the potential and btw 14kv static or DC is less than say
60 hertz. 14 kv. RMS, whre the peak potential is some 1.4 x 14 =
almost 20 kv.! And yes one can sometimes hear that hissing/corona on
33 kv and higher lines.
From: jamm on 17 Feb 2010 18:17
Thanks for the replies all. That makes sense.

--
*From the 1966 TV series:*
Robin: You can't get away from Batman that easy!
Batman: Easily.
Robin: Easily.
Batman: Good grammar is essential, Robin.
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