Why Substation Designs Reduce Grid Resistance but Increase Surface Resistance?
- Lower Grid Resistance Lower Earth Potential Rise (EPR)
During a fault, the grid can rise thousands of volts above remote earth.
Reducing Rg using more conductors, deep rods, conductive backfill, even salt) helps safely dissipate fault current and minimize voltage rise.
Goal: Protect equipment and the site as a whole from high EPR.
- Increase Surface Resistance Reduce Body Current
When someone is standing on the ground during a fault (especially near a fence or equipment), the danger is body current, not voltage alone.
By laying high-resistivity crushed rock (≥100 mm, p ≥ 3000 Q-m), we increase the foot-to-earth resistance, making it harder for current to flow through a person.
Goal: Protect people from electric shock via touch or step voltage.
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