Ground Resistivity, Overhead Power Line

[Yjoshi]

Dear all, we are building an overhead line in which the grounding design for each tower is a horizontal wire buried at a depth of 0,7m with a length from 30m to 120m for each tower leg (depends on the soil resistivity of each tower). To determine the soil resistivity the client spec refer us to use the Wenner method. My question is, considering the design that we intend to use, is the Wenner method appropriated and efficiently for us to follow?

 

[7anoter4]

You can state the method according to required accuracy of the measurement, number of work hours you can spend and number of workers. See [for instance]:

http://www.lightningman.com.au/Earthing.pdf

Remark: If you intend to use the result in order to follow the change with the time you need a more precision. For short-circuit calculation [using Endrenyi method for instance] I don't think the precision is so important.

 

[karls2]

Hi !
The Wenner method will allow you to determine the soil resistivity of the area were the wire will be buried.
These measures will allow you to increase accuracy when you will caculate the equivalent resistor of your earthing ground.
In some case it's possible to estimate the value (you can find some board on internet) following some samples of topsoil but it will be not the same value at 5 or 10 meters deepest.
The measuring depth change following the geometry of the earthing cable loop(additionnaly in some case you can have several layers with different resitance value).
More informations in 80-2000 - IEEE Guide for Safety in AC Substation Grounding.