## GPR in Concrete

## GPR in Concrete

(OP)

Dear experts,

I have not come across sufficient information to assist me in designing grounding system for a switchyard control building using IEEEStd80:2013.

I am seeking your expertise to advise me if my thoughts are incorrect?

1. GPR in concrete is different from GPR in soil.

2. a. What is the formula to calculate grid resistance of horizontal grid conductor (either separate copper ring or rebar) embedded in concrete? Eqns 63, 64 and 65 refer to ground rods encased in concrete, however if I am to use copper or the rebars embedded in concrete horizontally only. (some sections of the rebar might be vertical but not penetrating the soil.

2. b. Failing to find this equation in 2.a.(above) I used equation 57, I substituted the soil resistivity with the concrete resistivity to obtain the grid resistance, then multiplied this with the max grid current to obtain the GPR.

If my view of solving this problem is wrong, I would appreciate your expert views in pointing me the right way.

Thank you.

Yogima

I have not come across sufficient information to assist me in designing grounding system for a switchyard control building using IEEEStd80:2013.

I am seeking your expertise to advise me if my thoughts are incorrect?

1. GPR in concrete is different from GPR in soil.

2. a. What is the formula to calculate grid resistance of horizontal grid conductor (either separate copper ring or rebar) embedded in concrete? Eqns 63, 64 and 65 refer to ground rods encased in concrete, however if I am to use copper or the rebars embedded in concrete horizontally only. (some sections of the rebar might be vertical but not penetrating the soil.

2. b. Failing to find this equation in 2.a.(above) I used equation 57, I substituted the soil resistivity with the concrete resistivity to obtain the grid resistance, then multiplied this with the max grid current to obtain the GPR.

If my view of solving this problem is wrong, I would appreciate your expert views in pointing me the right way.

Thank you.

Yogima

## RE: GPR in Concrete

At first, when you calculate the permissible touch and step potentials. Then you use 27,32,33.

Second, when you calculate Ig [as Rf] and use 63

Third, when you calculate GPR=Ig*Rg then use 63

For Em and Es calculation only soil resistivity is considered.

## RE: GPR in Concrete

Appreciate sincerely your feedback.

I have covered item 1, item 2 and 3 are proving tricky as they refer to resistance calculation of vertical electrodes embedded in concrete.

For my case, am intending to use the rebars or run parallel copper conductor embedded horizontally in the concrete foundation (no rods penetrating soil) of the substation control building. I hope this clarifies why I am hesitant to use use eqn 63 or 64. I hope this has clarified my query more.

Thank you and appreciate you and other experts feedback.

Yogima

## RE: GPR in Concrete

You could consider the reinforced concrete foundation as an equipotential surface. Touch and step voltages within the building will be negligible. Touch voltage to the outside of the building will be the same as to any grounded structure.

If you really want to consider the voltage gradients in the foundation, you could model the rebar or embedded copper wire within a volume of concrete in a program such as SES CDEGS. I know of no way to do this by hand calculation.

## RE: GPR in Concrete

I appreciate your input here. I did not consider the the requirement to calculate the grid resistance, I now see how much of a pain that can be.

Thank you for the commentary on this.

Appreciative,

Yogima

## RE: GPR in Concrete

EasyPower Grounding Resource page and E&S Grounding blog have a lot of good information as well as free workshop on grounding studies.