Minimum Corona Free conductor sizes 3

[NAZ55]

Does anyone have a list/chart/reference standard for minimum corona free conductor sizes?

I will appreciate any information I can get.

Thanks

 

[edison123]

Corona is a voltage related issue. What conductor size has got anything to do with that ?

 

[magoo2]

There's an empirical formula for determining it called Peek's equation. It gives you the corona onset gradient in kV/cm.

I know the EPRI Red Book has some info on it. I'll see if I can find it and post some additional info. If you're not an EPRI member, it will cost you a kajilion dollars! : )

 

[waross]

Hi edison. Corona is also related to the effective radius of the conductor. One of the reasons that transmission cables are two-plexed, three-plexed and four-plexecd is to increase the effective radius and lower the corona losses.
Sorry, I don't have any charts or information.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[cloving]

Isn't corona a volts/length (circumference) issue? At high voltages, you experience corona at shapes that change abruptly or small conductors.

 

[magoo2]

As waross correctly points out, it depends on the conductor radius.

See if the attachment comes through OK. This is Peek's equation or formula from 1929.

 

[waross]

Thanks Magoo2;
Actually I think that the effective radius (in terms of corona onset/avoidance) of a four-plex bundle is much greater than the actual radius of the conductors comprising the bundle. Hence my use of the term "effective radius".

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Absolutely the effective bundle radius is greater than the individual radii. This is because one of the wires is in field created by the other conductors. This reduces the gradient.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[NAZ55]

I appreciate the input from all. The reason I asked this question is because I have an old Westinghouse sliders which actually gives a minimum corona free conductor size.

However I am not aware of any recent standards or references that may have this information to validate that data.

Thanks magoo for the equation. I will try it on a couple of conductors

A chart or table would be very handy or if you know of a standard name and number which may have this info.

 

[magoo2]

I agree, Bill. This equation is really designed to be used on a single conductor.

say zazmat,
What voltages are you dealing with

and

Are they single conductor lines or multi-conductor bundles?

 

[jghrist]

The Westinghouse T&D Reference Book (Chapter 3, IV Corona, pp. 56-62 in 4th edition) gives an equation somewhat different from Magoo's Peeks equation.

E_o = g_o·delta^(2/3)·r·m·ln(D/r)

where
E_o=critical disruptive voltage in kV to neutral
g_o=critical gradient in kV per cm (21.1 kV/cm, but Section 10 gives more accurate numbers and includes bundled conductors)
delta = air density = 17.9·b/(459+°/f)
b=barometric pressure in inches of Hg
r=conductor radius in cm
D=distance in cm between conductors for 1Ø or equivalent Ø spacing for 3Ø

m=surface factor (0.82 for stranded, 0.92 for segmental)

It also has corona loss curves for different conductor types.

 

[waross]

Star for you, jghrist.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[NAZ55]

Cool!

Thanks jghrist. This would even work on bundled conductors.

Magoo2 most of the lines I work with are 345, 138 and 69kV.

And 138kV and 345kV lines do require multi-conductor bundles.

Mostly

2-795kcmil, 2-1590kcmil ACSR and 2-2500kcmil AAC

Thanks all for your valuable input.

 

[davidbeach]

Bundled 138kV? If so, that is entirely for loadability and has nothing to do with corona. Single conductor 230kV with no anti-corona provisions at the insulator strings are extremely common. The only 345kV line I'm familiar with is single conductor, but does have anti-corona hardware at each insulator. There is even a fair bit of single conductor 500kV around - that one does surprise me, but I know its there.

 

[jghrist]

minor correction:

delta = air density = 17.9·b/(459+°F)