🔧 Engineering Decision Tool D3

GPR & Transfer Voltage

Interactive calculator

Ground Potential Rise (GPR) and transferred voltage assessment for substation grounding design per IEEE 80.

📐 Calculation Steps

1

Compute GPR

GPR = I_G * R_g

Ground fault current x grid impedance.

2

Mesh voltage

Em = rho*Km*Ki*I_G/L

Maximum voltage between grid and ground surface.

3

Compare to tolerable

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

Per IEEE 80 Table 7/8 for given soil resistivity.

🧮 Formula

GPR and Transfer Voltage

GPR = I_G*R_g; Em = rho*Km*Ki*I_G/L; Es = rho*Ks*Ki*I_G/L

IEEE Std 80 mesh and step voltage equations.

Symbol	Variable	Unit	Description
GPR	Ground potential rise	V
I_G	Grid current	A
R_g	Grid resistance	ohm
V_touch	Touch voltage	V
V_step	Step voltage	V

📋 Worked Example: 138kV Substation GPR

Result:

🔍 Result Interpretation

✅ V_touch < tolerable

✅ V_touch 1-2x tolerable

✅ V_touch > 2x tolerable

🔥 Guidance

Transferred voltage Any metallic path out of grid

Water pipes, fence wires, cable sheaths can transfer GPR to remote locations.

💡 Engineering Recommendations

🔧

GPR > 5000V

Install isolation joints on all metallic services 50m beyond grid.

SSB (Scotchply) isolation kits for pipes, fiber optic for telecom.

⚡ Quick Facts

5-25kV for HV substations

Typical GPR range

Counterpoise, deep wells, grid extension

Reduction methods

{V_touch50, V_step50} per soil type

IEEE 80 limit

🔬 Engineering Insight

"GPR does NOT kill - transferred voltage does. The real danger is when a remote fence, pipe, or cable brings the full GPR into an area of normal ground potential. Always isolate metallic services entering and leaving the substation."

📜 Standards & References

IEEE Std 80-2013 — IEEE

Guide for Safety in AC Substation Grounding.

↗

❓ Frequently Asked Questions

What is transferred voltage? ▼

When GPR travels along metallic conductors (cable shields, pipes, fence wires) to remote locations, creating a dangerous potential difference.

🔧 Related Calculators

→

Ground Resistance Calculator

→

Grounding System Design Calculator

📖 Related Knowledge

→ Substation Grounding Design

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