Grounding

[surineman]

I have a grounging study for a new water treatment plant.
We have to design the grounding system for this plant.
The plant is located on a granite rock outcorp and soil resistance clearly is high.
Depend on spacing of probes the resistance changes from 330 to 102.5 ohms.
we want to run a 4 odd cable along the storm sewer pipe (which is PVC) for nearly 200 ft and connect it to a ground rod buried 20 ft and backfill the hole with ground enhancemet material and have an extension pigtail for a grid connection just in case we have not got the appropriate resistance.
also we considered some ground rods around around the building and 24.9/600 v transformer connected to the 200 ft cable.
since I have never done a grounding design before, I gathered information here and there and I am not sure what I am doing.

Any references, materials, thoughts, helps would be highly appreciated

 

[peebee]

Check the IEEE Green Book, and the Erico website.

 

[surineman]

Can I use the duct bank used for primary cable to transforner for ground wire? should it be above or lower the power cables if possible?
Thx

 

[cuky2000]

The application described with high soil resistivity may be a challenge even for experience engineers using conventional design approach.

In spite of the negative impact of high soil resistivity, the good news is your project has several elements such as large concrete structures, pipes, rebar, water, etc if use properly could help to made significant improvement reducing the material and construction cost of a grounding system.

Take advantage of those good elements using available commercial software with capability to model foundation with high moisture and underground metallic structure. Beware that good grounding software are not cheap and the learning process may slow the project. Other option is to hire a consulting firm/engineer with grounding experience and software license to do this work.

 

[RalphChristie]

Download RUS Bulletin 1724E-300, Design Guide for Rural Substations:

http://www.usda.gov/rus/electric/pubs/1724e300/1724e300.pdf

Ch9, pg501

 

[surineman]

Ralph,

Thx for reference but it seems the website facing some difficulties.

Regards,

 

[cuky2000]

Surineman,

Download the file saving it in your system. That may work in your computer.

The grounding section is OK for standard substation ground grid following the general guidelines from the IEEE Std 80. However, the deterministic method recommended have limited application since is difficult or almost impossible to model foundations, underground pipe and other components.

You have the final choice either pay extra in construction phase or pay extra during the design phase.

For comparison purposes, see the enclose information.

http://www.sestech.com/Products/SoftPackages/AutoGroundDesign.htm

http://www.cyme.com/software/cymgrd/

 

[RalphChristie]

Surineman

Maybe you have to use cuky2000's advice, download the file saving it in your system. I am still able to open it, but beware, it is a rather big file. (10MB) It is full of useful information regarding substations, such as grounding issues, etc.

Regards
Ralph