Re: Corona breakout voltages?

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

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Terry and all,

Antonio's and Jim's previous posts explain the reasons for the lack of 
corona on high voltage transmission lines. As Jim indicated, utilities 
often use "bundles" of spaced conductors for each phase to increase the 
"effective" diameter of the conductor for higher voltage lines. These 
can range from 2 (most common) to 8 (for EHV transmission lines). But 
even more importantly, as Antonio indicated, the surface E-field for a 
HV wire over a conducting plane is much lower than one would think just 
looking at conductor diameter, so that it's operating voltage can be 
much higher before corona begins.

The combination of these two effects significantly decreases the maximum 
E-field seen at the HV conductor's surface... to the point where it's 
brought below the corona inception voltage! High voltage and EHV AC 
transmission lines are typically designed so that the maximum surface 
voltage gradient typically falls in the range of 13 - 18 kV/cm RMS (or 
about 18-25 kV/cm peak).

For those wanting to do a bit more research on AC corona and HV power 
transmission, some excellent sources include:
1. Electric Power Research Institute (EPRI), “Transmission Line 
Reference Book 345 KV & Above”, 2nd ed, Revised, EPRI., 1987, 625pp

2. Begamudre, R. D., “Extra High Voltage AC Transmission Engineering”, 
2nd ed., New Age Int’l Publ., 1997, 580pp

Best regards,

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
"Electromagically" (TM) Shrunken Coins!
http://www.teslamania-dot-com


Tesla list wrote:
> 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...
> 
> 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?
> 
> Cheers,
> 
> 	Terry
> 
> 
>