Re: Corona breakout voltages?

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Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>


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From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, October 12, 2002 7:41 PM
Subject: Corona breakout voltages?


> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>
> Hi All,
>
> There is this well known formula for corona of 3MV per meter of radius.
If
> I have a 1 meter radius sphere, I can but 3,000,000 volts on it before
> corona breaks out.
>
> So I used to work on 375kV power lines, they were about 1 inch in diameter
> (0.0127m radius).  0.0127m radius suggest a corona voltage of 38,100
volts.
>  So at 10X that, those lines should have been glowing and streamering like
> crazy!!!  375kV was also an "RMS" voltage...

But, were those "bundled" lines, which increases the effective radius?
Also, corona inception voltage isn't exactly matched to free air breakdown
field... you can get a low grade corona which creates a semiconducting
ionized sheath increasing the effective diameter of the conductor..not that
I'd want to get anything grounded near it, for the flashover potential is
high, but, out in free space, you might get some crackle and hiss, but not a
whole lot of visible corona (in UV on the other hand...).   You'll see
corona rings at the insulator strings, too..

>
> I am having trouble getting little spheres to corona at the voltage I
think
> they should (seems to take far far higher voltage) and I think what ever
> held corona back on those high voltage power lines is also holding back
> corona in my sphere experiments.  Is the surrounding air just charged up
> and acts to reduce the e-field or something???
>
> I am just wondeing if anyone has any insight into this or can tell me what
> I am missing in all this?

HV is strange...

Mostly, there's a big difference between uniform and nonuniform fields, in
terms of observed effects.  Running small diameter conductors at high
voltages, you've got a nonuniform field.