Electric field - ground clearance relation

[akle]

Hi,

while dealing with electric field radiated by high voltage transmission lines, I thought that the formula E = I / 2*pi*eps0*r*c (by faradays law for a long line) is enough for me to calculate electric field. it is obvious that electric field should drop down as r - distance increases.

 

but when I took a look on literature I saw figures showing that electric fields values increases for some meters away from conductors after it drops down. literature says that its because of ground clearance, what they mean. how can I calculate ground clearance and apply to formula of electric field?

 

any help is appreciated ...

[lawcat]

I am an electrical engineer, and I don't know a whole lot about this. The best I can tell you is, follow published tables for safe ground clearance.

 

As far as the electric field, it's calculated considering 1) type of conductors (some are twisted and have non linear field distribution as electrons flow), 2) phasing of current, 3) sag and shape of the line, 4) effects of ground current induced by line's magnetic field. In other words, geometry makes electric field distribution nonlinear. Correct calculations are done using vector matrices, and when modeled, the nonlinear results agree with observation. The best answer I can give you is, the geometry makes it so, nonlinear and "counterintuitive."

 

Remember, the electric field is a vector field. Most phenomena are nonlinear. The linear idea of electric field stems from Gauss law, which is a simple special case of one charge, or infinite conductor, and in most application it is just a useful approximation. In this case, you are asking for a specific formula where we can not apply the approximation for accuracy purposes. Due to geometry, vector values add up in nonlinear fashion. For that, a particula set of vector formulas is developed to agree with observations. You need to consult literature and I don't have that info.