Comparison and contrast between the underground cables and overhead lines in distribution systems

• Maintenance costs:
The present worth of the maintenance costs associated with underground lines is difficult to assess. Many variables are involved, and many assumptions are required to arrive at what would be a guess at best. Predicting the performance of an underground line is difficult, yet the maintenance costs associated with an underground line are significant and one of the major impediments to the more extensive use of underground construction. Major factors that impact the maintenance costs for underground transmission lines include.

• Cable repairs:
Underground lines are better protected against weather and other conditions that can impact overhead lines, but they are susceptible to insulation deterioration because of the loading cycles the lines undergo during their lifetimes. As time passes, the cables' insulation weakens, which increases the potential for a line fault. If the cables are installed properly, this debilitating process can take years and might be avoided. If and when a fault occurs, however, the cost of finding its location, trenching, cable splicing, and re-embedment is sometimes five to 10 times more expensive than repairing a fault in an overhead line where the conductors are visible, readily accessible and easier to repair.

• Line modifications:
Overhead power lines are easily tapped, rerouted or modified to serve customers; underground lines are more difficult to modify after the cables have been installed. Such modifications to underground power lines are more expensive because of the inability to readily access lines or relocate sections of lines.

• Appearance:
The general appearance of the underground system is better since all the distribution lines are invisible. The conductors are visible and easily accessible in overhead system.

• Flexibility:
Underground cables are less flexible since manholes, duct lines etc. but overhead line are more flexible due to poles, wires, transformers etc. Those can be easily shifted to meet the chances in load conditions.