220kV GIS (Indoor) - Earth grid design

[RRaghunath]

GIS occupies much less space when compared with AIS. While this makes it desirable in places where the space is at a premium, it poses a challenge when it comes to designing the earth grid for the installation.
The location is with high soil resistivity and would it be advisable to embed the grid in the floor concrete to take advantage of the decreased resistivity!
Appreciate any advice / references.

Thanks

 

[raadhatab]

the resistivity of earthing system should be less than 1 ohm,embiding it in the concrete floor are subjected to many variables,i suggest to add some salts to the earthing rods in the yard to obtain the required resistivity

 

[RRaghunath]

Thank raadhatab for the opinion. I am afraid that it is not adequate for the indoor GIS with limited space available (treated earth pits are used widely otherwise).

 

[cuky2000]

Investigate if the following may be feasible to consider:

* Specify long ground rods
* Use diagonal counterpoises.
* Reduce soil resistivity with soil enhancement.
* Use the concrete and rebar as supplementary ground electrode.
* Interconnect ground grid if any close grid (Pwr plant, substation, etc.).
* Use the injected current to ground instead the full SC current.

 

[HiSet]

Although Earth Grid should be designed to carry full short circuit current for 3 sec yet step and touch potential should be calculated based on max single phase ground fault current at the location keeping in mind appropriate appropriated distribution factor.