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Which of the following transmission line have more initial cost?
Overhead Transmission
Underground transmission
Both have almost the same initial cost
None of the above
Underground transmission
Underground transmission lines involve significantly higher initial costs compared to overhead transmission lines. This is primarily due to the complex installation requirements, including expensive underground cabling, specialized insulation materials, and intensive labor for excavation and trenching.
Underground transmission lines involve significantly higher initial costs compared to overhead transmission lines. This is primarily due to the complex installation requirements, including expensive underground cabling, specialized insulation materials, and intensive labor for excavation and trenching.
CtotalтАЛ=ClandтАЛ+CcablingтАЛ+CtrenchingтАЛ тАФ Basic cost estimation model for underground systems
The cost disparity arises because underground cables require robust insulation (dielectric materials) to withstand high voltage in proximity to earth and surrounding materials, whereas overhead lines use air as a natural, free insulator. Furthermore, underground construction involves civil engineering challenges such as conduit installation, thermal management, and protection against moisture and mechanical damage, all of which are absent in overhead transmission construction.
Overhead lines use bare conductors with air as the primary insulation.
Underground cables require complex multi-layered construction including conductor, insulation, screen, armor, and serving.
Repair costs for underground faults are also significantly higher than overhead lines.
Underground cables have higher shunt capacitance, requiring compensation at higher voltages.
Less susceptible to lightning and weather interference
No visual pollution (aesthetic)
Higher safety in crowded urban areas
High initial cost
Difficulty in locating and repairing faults
Limited current carrying capacity due to thermal constraints of insulation
Highly congested urban areas
Vicinity of airports and defense installations
River or water body crossings
| Feature | Overhead | Underground |
|---|---|---|
Initial Cost | Low | High |
Insulation | Air | Solid/Polymeric |
As a rule of thumb, for higher voltages, underground cabling can cost 5 to 15 times more than equivalent overhead lines.
Option A is incorrect because overhead lines rely on simple lattice structures and air, keeping costs minimal compared to the civil engineering required for cables.
B is correct тАФ Underground transmission involves massive expenses related to specialized high-voltage insulation and civil work for subterranean installation.
In exams, remember that while underground transmission is aesthetically superior and safer from external weather, its economic viability is limited to urban or high-security zones.