RE: this was probably really stupid

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 05:22 PM 5/26/2004 -0600, you wrote:
>Original poster: "Daniel Kline" <daniel_kline-at-med.unc.edu>
>
>
> > -----Original Message-----
> > From: Tesla list [mailto:tesla-at-pupman-dot-com]
> > Sent: Wednesday, May 26, 2004 1:35 PM
> > To: tesla-at-pupman-dot-com
> > Subject: Re: this was probably really stupid
> >
> >
> > Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>
> >
> >
> > Ed:
> >
> > I have always wondered how these long distance EHV lines
> > avoid producing
> > excessive corona.
> >
> > The cables do not appear to be very large in diameter ---
> > perhaps an inch or
> > two at best.  With that small radius and diameter, why don't they emit
> > tremendous corona?
> >
> > With corona inception potential around 67 kV per inch (30
> > kV/cm) they should
> > be glowing a lot with their small diameters.  Especially in
> > rainy weather.
> >
> > Dr. Resonance
>
>Down in the Florida Keys, the transmission lines have corona where the
>wires contact the insulators.
>It's a constant "snap, crackle and pop" too. It takes a few minutes to
>get your eyes accustomed to
>the necessary darkness, but I've seen it several times. I'm guessing the
>humid salt air has something
>to do with it. Next time, I'm taking a pair of binoculars so I can see
>the effect "close up".
>Dan K.
Probably more surface arcing over the dirty insulator surface.  In normally 
dry southern CA, you know when the humidity comes up because you get more 
insulator noise.

They have UV cameras to look for corona losses on the cables (and 
insulators), and on some HV lines they use large donut shaped corona 
reducers at insulators.

Corona loss is a big deal in the power industry, because it's a non-revenue 
generating use of power.

Khalifa gives a formula:

Pc = 3.73*k/(D/r)^2 * f * V^2 * 1e-5

kW/conductor/km
f = frequency (Hz)
V line voltage
D phase conductor separation
r phase conductor radius
k is a factor depending on the ratio of working voltage to corona onset 
voltage k=1.0 for V/Vo =1.4

Typical values are 0.3 to 1.7 kW/conductor/km for 500 kV lines

For bundles... Emax (Max field) = V/ln(4*h^2/(r*d)) * (1/r + 1/d)
V is voltage
h is height above ground, d is distance between conductors in the bundle, r 
is the radius of the bundle conductor.