🔧 Engineering Decision Tool D3

Grounding System Design Calculator

Multi-tab calculator for Grounding System Design

Grounding system design calculates grid resistance, step/touch voltages, and conductor sizing per IEEE Std 80-2013 for substation safety.

📐 Calculation Steps

1

Define grid geometry

Area, spacing, conductor length, depth.

2

Calculate grid resistance

Rg = rho*(1/L+1/sqrt(20A))*(1+1/(1+h*sqrt(20/A)))

Sverak's equation.

3

Mesh voltage

Em = rho*Km*Ki*IG/L

Maximum voltage between grid and surface.

4

Compare to tolerable

E_touch50 = (1000+1.5*Cs*rho)*0.116/sqrt(ts)

Per IEEE 80 Table 7.

🧮 Formula

Grid Design per IEEE Std 80

Rg = rho*(1/L_T + 1/sqrt(20*A))*(1+1/(1+h*sqrt(20/A))); Em = rho*Km*Ki*IG/L_T; Es = rho*Ks*Ki*IG/L_T

Sverak's grid resistance equation and IEEE 80 mesh/step voltage equations.

Symbol	Variable	Unit	Description
R_g	Grid resistance	ohm
A	Grid area	m2
rho	Soil resistivity	ohm-m
L_T	Total conductor length	m
I_G	Maximum grid current	A
h	Burial depth	m

📋 Worked Example: 138kV Substation Grid

Result:

🔍 Result Interpretation

✅ Em < tolerable

✅ 1-2x tolerable

✅ > 2x tolerable

🔥 Guidance

High GPR > 5000V

Transferred voltage risk to remote equipment.

💡 Engineering Recommendations

🔧

Em > tolerable

Add more cross conductors (reduce spacing).

Halving spacing doubles conductor length, reducing Em by ~45%.

⚡ Quick Facts

0.5-5 ohm for substations

Grid resistance typical

Up to 5000 m2 grid area

IEEE 80 valid range

🔬 Engineering Insight

"The biggest design margin comes from adding perimeter conductors. For grounding grids of a given area, mesh voltage decreases approximately linearly with conductor length, while grid resistance plateaus after ~2000m."

📜 Standards & References

IEEE Std 80-2013 — IEEE

Guide for Safety in AC Substation Grounding.

↗

❓ Frequently Asked Questions

What is GPR? ▼

Ground Potential Rise: the voltage rise of the grounding grid relative to remote earth during a fault.

🔧 Related Calculators

→

Ground Resistance Calculator

→

GPR Transfer Voltage

📖 Related Knowledge

→ Substation Grounding

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