For a large power station, earth resistance should be extremely low so high fault currents can return safely and protective devices operate quickly. The exam's IS 3043-based target is ideally not exceeding about 0.5 Ω.
Formula / Key Relation
Earth-potential rise:
EPR ≈ Ifault × Rgrid
Lower Rgrid → lower EPR for the same ground-fault current
Detailed Explanation
Concept & ReasoningLarge substations/power stations use extensive earth grids to limit earth-potential rise and touch/step voltages during faults. A lower resistance is desirable because the available fault current is large and personnel/equipment safety is critical. Actual design also requires grid-potential and touch/step-voltage calculations, not resistance alone.How to Solve It in the ExamLarge power station → very low earth resistance, ~0.5 Ω target in exam tables.Important Exam PointResistance is one criterion; safe touch/step voltage is the deeper design objective.Related Revision PathThis question sits in the revision path Electrical Laws, Standards and Energy Policy → Indian Standards → Earthing Design .
Concept & Reasoning
Large substations/power stations use extensive earth grids to limit earth-potential rise and touch/step voltages during faults. A lower resistance is desirable because the available fault current is large and personnel/equipment safety is critical. Actual design also requires grid-potential and touch/step-voltage calculations, not resistance alone.
How to Solve It in the Exam
Large power station → very low earth resistance, ~0.5 Ω target in exam tables.
Important Exam Point
Resistance is one criterion; safe touch/step voltage is the deeper design objective.
Related Revision Path
This question sits in the revision path Electrical Laws, Standards and Energy Policy → Indian Standards → Earthing Design .
Quick Trick
Large power station → very low earth resistance, ~0.5 Ω target in exam tables.
Common Mistake
Applying a domestic installation earth-resistance rule to a large station grid.
Exam Tip
Resistance is one criterion; safe touch/step voltage is the deeper design objective.
SEO + Knowledge GraphRelated PYQs & Exam ContextExam path, knowledge path and deeper practice links.
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