- 2069 Bhadra · 4 marks
Underground cables vs overhead lines
Short answer
Underground cables have higher cost, better safety, lower inductive reactance, higher capacitance, and harder fault repair; they are used in congested areas. Overhead lines are cheaper, easier to repair, suited for long-distance high voltage, but are exposed to weather and faults.
Compare underground cables with overhead lines.
Overhead lines carry bare conductors on insulators and towers. Underground cables carry insulated, sheathed conductors buried in the ground.
| Point | Underground cable | Overhead line |
|---|---|---|
| Initial cost | High (5–10 times) | Low |
| Insulation | Solid or oil insulation all along the length | Air, plus insulators at the supports only |
| Working voltage | Limited (insulation and charging current) | Can be very high (765 kV and above) |
| Fault chances | Few (no lightning, storm or bird faults) | More (exposed to weather and accidents) |
| Fault location and repair | Difficult and slow (digging needed) | Easy and quick |
| Charging current | High (large capacitance) | Low |
| Inductive reactance | Low (conductors close together) | High |
| Heat dissipation and current rating | Poorer | Better |
| Appearance and safety | No visual impact, safe for the public | Spoils the view, with risk of contact |
| Flexibility and extension | Poor | Easy to tap and extend |
| Interference with communication lines | Negligible | Possible |
Cables are used in cities, substations, river and sea crossings, and airports. Overhead lines are used for long-distance, high-voltage transmission.
✓ Answer checked by Claude Opus 5.5 (high effort)
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