Overhead Versus Underground System

OVERHEAD VERSUS UNDERGROUND SYSTEM

The distribution system can be overhead or underground. Overhead lines are generally mounted on wooden, concrete or steel poles which are arranged to carry distribution transformers in addition to the conductors. The underground system uses conduits, cables and manholes under the surface of steels and sidewalks. The choice between overhead and underground system depends upon a number of widely differing factors.

1. Public safety

UG cable is preferred, as there is less chance of any hazard to the public.

2. Initial cost

The underground system is more expensive due to high trenching, conduits, cables, manholes and other special equipments. The initial investment on UG cable system is about 10 times the rate on OH line system.

3. Flexibility

The overhead system is move flexible than the underground system. The overhead line system can be modified easily.

4. Faults

The chances of faults in underground system are very rare as the cables are laid underground and are generally provided with better installation.

5. Appearance

The general appearances of an underground system is better as all the distribution lines are invisible.

6. Fault location and repair

Fault location and rectification of fault is easier in OH line system. In underground system, if a fault does occur, it is difficult to locate and repair.

7. Current carrying capacity

An overhead distribution conductor has a considerably higher current carrying capacity than an underground cable of the same material and cross section.

8. Useful life

The useful life of underground system is much longer than that of an overhead system. An overhead system may have a useful life of 25 years, whereas an underground system may have a useful life of more than 50 years.

9. Maintenance cost

The maintenance cost of UG cable system is low, as the chance of fault is less in an UG cable system.

10. Interference with communication circuits

An overhead system causes electromagnet interference with the telephone lines. The power cable currents are superimposed on speech currents, resulting in the potential of the communication channel being raised to on undesirable level. However, there is no such interference with the underground system.