steel ground grid

[hamid66]

Hi
I would like to have some information for using steel instead of copper in substation ground grid. Although the main problem is corrosion and it should be considered in design stage.
I would like to know if in your HV substation steel is being used and what type of conductor (Galvanized steel stranded wire / al clad steel stranded wire/rectangular cross section steel bar) is prefered.
How about their connection welding/exothermic welding/ bolt /clamps/...)

 

[marks1080]

It doesn't sound like a good idea. Copper is certinaly the best bet. You do see more copper clad steel these days in an effort to combat copper theft. Typically you don't know of a failure in the ground grid until it's too late. Steel would be more prone to failure I would think.

 

[ScottyUK]

Many years ago cast iron plates were used as earth electrodes. Cast iron was relatively cheap, and it has better corrosion resistance than steel. I'm not aware of anyone using steel as an earth electrode. A stainless steel might have more merit, depending on your soil chemistry, although that is purely speculative.

 

[Kiribanda]

hamid66,
If you are putting the ground grid near a CP (Impressed current type) protected underground steel structure such as pipe lines etc,
then you cannot use Copper for your ground grid. Because once your Copper grid is in operation there are hundreds of intentionally
and unintentionally connected bonding paths between Copper grid and Steel structure. As a result you will see that the rectifier
transformers associated with the CP system are loaded. Also since Copper is the noble metal, steel will get corroded and may disappear
after sometime. Therefore, if you are having such a CP situation, my advise is to design & install the ground grid with Galvanized
steel wires and rods instead of Copper and to use exothermic (CADWELD)connections even though expensive than compression connections.
Having said that, if Copper is used, there are methods (eg. DIARYLAND insulators) to isolate intentional bonds of the two grids
but depending on the installation it will be practically difficult to break unintentional bonds.