The underground cables have several advantages such as less liable to damage through storms, lightning, low maintenance cost, less chances of faults, smaller voltage drop and better general appearance. Voltage drop is also an important factor of cable design. Underground cables consists of one central core or a number of cores (two, three or four) of tinned stranded copper conductors (sometimes use of aluminium conductor is also made) insulation from each other by paper or varnished cambric or vulcanized bitumen or impregnated paper.Typically overhead lines are more common in rural areas as they are used to cover greater distances. Underground electricity cables are laid below the ground and are usually found in built up areas such as cities.
There is no requirement of digging, manholes, and trench. So, the overhead line system is cheaper than the underground system. The initial cost of the underground transmission system is more compared to the overhead line because it needs digging, trenching, etc.
As overhead line exposed to the environment, the chances of faults are more. The cables are not exposed to the environment, there is less chance of fault.
This system is less safe as the conductors placed on the towers. This system is safer as the cables placed underground.
In this system, useful life is approximately 20 to 25 years. Useful life is approximately 40 to 50 years.
The general appearance of this system is not good because of all lines are visible.The general appearance of this system is good because of all lines are invisible.
In this system, no need to dig at the time of maintenance. Hence, for the same number of faults, the maintenance cost is less. In this system, to find the fault, digging is compulsory. It increases labor cost. Hence,