Program for grounding analysis

[Alex68]

hi friends,
I'm looking for a CHEAP but effective software for the grounding grid analysis. Could you suggest anything?

On the other hand, I could write by myself the prg, if somebody could suggest the basic algorythm.

Thank you
Alex68

 

[jwerthman]

We use the Ground Grid Design module from the ETAP program by Operation Technology, Inc. at

http://www.etap.com.

Two others that I am aware of are by SKM at

http://www.skm.com

and CYME at

http://www.cyme.com.

 

[Alex68]

Thank you, jwerthman

I know very well these programs.
Usually I use CYMGRD, its biggest problem is the high cost.
All of these programs don't import the grid from Autocad, exept for CYMGRD because I asked to add this possibility.

I think that the best prg is produced by Sestech, that is by Mr. Dawalibi, "the earthing man"!

I'm looking for something cheaper if possible. I would like to start an indipendent activity but the initial budget is low. I'm ready to write by myself the prg, if sombody could suggest the basic algorythm

 

[jghrist]

We use the SES program. It is an excellent program, but as you say it is not cheap. I don't think there is a good cheap program.

You could do a simplified analysis on a spreadsheet or math program like MathCad, based on the calculations given in IEEE std 80, Guide For Safety In AC Substation Grounding. To adequately handle complex grid layouts or multi-layer soils, however, you would need to write a very complex program. A couple places to start would be:

F. Dawalibi, D. Mukhedkar, "Optimum design of substation grounding in two layer earth structure", Part I, II, & III, IEEE Transactions, Vol. PAS -94, No. 2, Mar/Apr 1975, pp. 252-272.

F. Dawalibi, D. Mukhedkar, "Multi-step analysis of interconnected grounding electrodes", IEEE Ttransactions, Vol. PAS -95, No. 1, Jan./Feb. 1976, pp. 113-119.

If you did attempt such a complex program, it should be tested extensively and verified before using it for a safety-lated application such as grounding design.

 

[Alex68]

Thank jghrist

I've already prepared a spreadsheet based on IEEE 80-2000, but it isn't sufficient for medium and large grounding grids.

I would like to write a prg, using the cymgrd results and the measuraments for testing it until I have the possibility.

Thank you for the suggestion of some papers

 

[Breaker]

An alternative grounding analysis program you might like to look at is GROD2002. You can find details of it on the following website:

http://www.era.co.uk

 

[Alex68]

Thank Breaker,
I will try

 

[GordS]

I can suggest 2 papers that give the algorithm for ground grid analysis. First, IEEE Transactions on Power Delivery Apr 2002 pg 596 gives the method for calculation whereone has finte volumes of resitivity within a certain background resistivity.

IEEE Transactions on Power Delivery Jan 1997 pg 179 is limited to systems where soil is modelled in layers. The paper describes how to handle the 2 layer case. It relies in the developement of self and mutual inductances between grid elements.

Both algorithms can be done in Excell by writing a macro. I found the first one more generic because it is possible to model multiple layers (each layer is modelled by a rectangle of given resitivity that is much greater than the size of the grid) in addition to finite volumes such as rocks and ponds. I suppose the second paper can also deal with multiple layers but keeping track of all of the images becomes fearsome.

 

[jghrist]

You're a better man than me, GordS, if you can set and solve the set of linear equations from the Apr 2002 paper with Excel. We have the SES software developed by the paper's authors. It would be interesting to compare this with your Excel results. If you have a fairly simple system, I'd be glad to set it up on the SES software for comparison. My email address is jghrist@utilitytec.com

 

[Alex68]

Thanks Gords for your suggestion and congratulations for your Excel files.

I have already developed by myself a software based on some pubblications. Starting from the resistivity measures and the Autocad drawing of the grid, I build the 2 layers soil model and then I can calculate:
the grid resistance, the GPR, touch and step voltage, profiles, touch voltage surfaces.

I tested it with good results, I could give you all the report of the comparison with the examples of IEEE80-2000 and with the results of CYMGRD.

Moreover I would like to compare my prg with the Gords' one

 

[jbartos]

Suggestion: It is a good idea to verify if the Client system accepts other software kinds and results than specified. Grounding grid design results are verifiable in the field. Some modifications of the grounding grid might result if the grounding grid parameters are insufficient.

 

[Alex68]

In Italy, electrical codes impose to measure the equivalent resistance and the touch voltages every two years in power plants.
So I have compared the results of my prg with the measures. The prg is OK. The differences are negligible.

If a Client imposes a particular prg, I'm out. But it imposes only a Standard, I can propose my prg with the validation report.

 

[jghrist]

It isn't easy to verify touch potential results in the field. You can inject a current and measure touch potentials on a grid not connected to transmission line shield wires. This could verify the touch potential related to the calculated earth current. The calculated split of ground return current between the earth and shield wires is very important and I don't know how that can be field verified short of injecting the current through the transmission line itself. The amount of fault current returning through the transmission line shield wires depends on the mutual coupling between the conductor and the shield wire and between the conductor and earth return.

 

[Alex68]

You're right! the measurament are not simple.
The italian standard is very complex and requires expensive instruments. Only a few societies are able to do accurate measuraments.

 

[jbartos]

Comment: The Utilities have specifications and procedures that have to be followed for the grounding grid engineering, design, construction, and testing.

 

[jghrist]

GordS,

I have analyzed two sample grids that you sent me by e-mail with the SES MALT program, for comparison with your Excel program.

Case 1:
0.5 m deep 50m x 30m grid in 2000 ohm-m soil, 8 meshes by 4 meshes. 0.01 m radius conductor. 1000A fault. Grid corners at (x=0, y=0), (x=50, y=0), (x=0, y=30), (x=50, y=30).

Grid resistance - 23.45 ohms
GPR - 23450V

Maximum touch voltage within grid area - 4900V directly over the four corners. Touch voltage inside grid at (x=2, y=2.5) - 4827V (other corners the same). Touch voltage at (x=-1, y=-1) - 8627V (other corners the same).

Maximum step voltage - 2856V at (x=0, y=7.5). Step voltage is about the same along the short sides close to cross conductors.

Case 2:
0.5m deep 18m x 12m grid in 300 ohm-m soil with a vertical cylinder of 50 ohm-m soil (10m diameter centered at x=0, y=0). Equal size 2 x 2 meshes. Conductor radius 0.005m. Grid corners at (x=2, y=0), (x=20, y=0), (x=2, y=12), (x=20, y=12). 1000A fault.

Grid resistance - 7.693 ohms
GPR - 7693V

Maximum touch voltage - 2370V at (x=17, y=9.5). Touch voltage in mesh closest to 50 ohm-m cylinder is lower (<2155V).

Maximum step voltage - 1309V at (x=20.5, y=6). Step voltage on side near 50 ohm-m soil is lower (<1178V).

How does this compare to your results?

 

[GordS]

Thanks jghrist for taking the time to check my results.

Case 1 used the formulation of self and mutual impedances between grid elements. I get the following:
Grid R = 23.9 ohms
Touch volts within grid = 5271
Touch volts at (-1,-1) = 9042
Vstep = 1818 volts in the same area as you noted (looks like I am way out on this value)

Case 2 was based on the first of the papers I referenced. I get 5.43 ohms for the grid resistance.

This same grid was modelled in the Transactions on power Delivery, July 2000 in a paper entitled &quot;Analysis of Grounding Systems in Soils&quot; where the result was 5.5 ohms.

My maximum touch voltage calculates to 4130 V at (10.5,0). My step voltage is 706V (from (11,0) to (11,2). The touch voltages within the low resistivity cylinder are about 10% lower than outside the cylinder. The touch voltage at (17,9.5) comes to 3690 V.

Again thanks for yout time. Not sure if I feel good or bad about the results.

 

[busbar]

Addressing the original inquiry re CHEAP, there is

http://members.aol.com/ocsoft/13.htm

that apparently is an IEEE 80 and 142 grounding-grid DOS application for $550. I know nothing else about the material or firm offering it.

 

[jbartos]

Comment on the above calculations. Normally, I do have to present a number and size of ground rods to the Utility since they impact the touch and step potentials. The feasibility of ground rod locations is sometimes available from the grounding preliminary study or grounding schematics.

 

[jghrist]

On the calculation comparison:
Case 1 results are very close. Case 2 is considerably different. I wonder why your touch voltage is much more than mine but your step voltage is much less. Your calculations are based on a paper written by the developers of the software I used, so the theoretical basis should be the same. I suspect either my input has an error (I will check), your input has an error, or your program has an error. This is the first time I have used a cylindrical soil model. One thing I note is that the calculation time is much longer. I calculated potentials every 0.5m over a surface extending 5m outside the grid (28m x 22m, about 2500 points). I didn't time the run, but it took well over 1/2 hour on a PC.