A comparison of Overhead and Underground Transmission

Electric Power needs to be carried over long distances from the point of generation to the point of consumption.  This Transmission is done either through overhead lines or underground cables.  Each of these two methods of transmission has its own advantages and disadvantages. 

Overhead Transmission lines are cheaper as the insulation cost is lesser and the conductor material cost is lesser too.  They also have better heat dissipation.

However, they have significant disadvantages.  Overhead lines are vulnerable to lightning strikes which can cause interruption.  Overhead lines use  bare conductors and can cause damage if they break.  They are considered to be unsightly as they mar the scenery of the landscape.  The maintenance cost of overhead lines is more and the voltage drop in overhead lines is more.

Underground transmission due to cables is costlier than overhead transmission as the ground needs to be excavated.  This can be difficult when passing though geographic obstructions such as hills, marshes and rivers.  Special trenches need to be constructed when passing through loose soil.  Besides, heat dissipation in underground cables is an issue. Hence,  the conductors have to be thicker.  The insulation required for the cables is expensive.  Hence, it is difficult to use underground cables for voltages at HV levels (> 33 kV).  

Underground cables may have to be rerouted to accommodate other underground structures such as pipelines, sewage lines, etc.    It is necessary that the routes of underground lines are clearly marked with sign boards to prevent accidents when excavations are carried out for other reasons at a later date. 

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