The distribution system can be overhead or underground.Undergrounding is more expensive, since the cost of burying cables at transmission voltages is several times greater than overhead power lines, and the life-cycle cost of an underground power cable is two to four times the cost of an overhead power line.
The overhead lines are mounted onsupports like wooden, steel, RCC, Reinforced plastics. The underground cables require digging trenches and this may be complicated by other utility service lines such as water pipes, oil and gas pipelines, sewer lines. Other complications may arise due to rocks, loose soil and water along the routes, making them more expensive to install.
|Sr.no||Features||Overhead system||Underground system|
|1||public safety||All the conductors with high voltages are placed overhead. Therefore less safer compared to underground system||All the distribution wiring is placed under the ground. Therefore safer.|
|2||Initial cost||Initial cost is less compared to underground system||Initial cost is high due to the high cost of trenching, conduits, manholes, and other special equipments.|
|3||Flexibility||In this, the poles, wires, transformer, etc can be easily shifted to meet the changes in the load conditions. Thus more flexible||In this, the manholes, duct lines, etc are placed permanently once installed and the load expansion can be met by laying new lines only.|
|4||faults||Fault chances are comparatively high (due to lightning’s, insulation failure ,etc)||The chances of faults here are less since all the wiring is underground and is provided with insulation.|
|5||appearance||The appearance of overhead line is not so good.||All the distribution lines are kept underground. So it gives better appearance.|
|6||Fault location and repairs||The conductors are visible and are accessible so the fault can be located and repaired easily.||Generally, there are very less chances of faults in an underground system. But if at all any fault occurs, then it becomes difficult to locate it and repair.|
|7||Current carrying capacity and voltage drop||It has considerably higher current capability.||It has comparatively low current capability.|
|8||Useful life||25 years.||More than 50 years|
|9||Maintenance cost||Due to the chances of faults and service interruptions in an overhead system due to wind,ice,lighting as well as from traffic hazards , the maintenance cost of overhead system is high||As compared to the overhead system the maintenance cost is comparatively less due to less chances of faults|
|10||Interference with communication circuits||An overhead system causes electromagnetic interference with the telephone lines.||In underground system there is no such interference.|
The underground cables are more expensive to construct and install, however, they are convenient, less likely to break and mostly used to provide the missing link where overhead cables cannot be used. The choice of the cable to use is determined by the particular situation. The overhead cables are widely used due to their cost and ability to carry more power compared to the underground.