The two recent hurricanes, Helene and Milton, have devastated power lines in many places but especially in Florida and N. Carolina. Florida Power estimates that underground lines fared 12 times better than lines that were overhead during the hurricanes.
There are two situations utilities face, depending on whether it is a new installation or a change from aboveground to underground. In either case there are several OM factors that are discussed in your textbook that are relevant when deciding whether to use overhead lines are below ground lines.
Fixed costs In general, underground lines require trenches and manholes which are more expensive to build than erecting pylons/poles for overhead wires. Also, underground wires require special insulation. The cost of installation can vary depending on the locality. Underground lines cost 5-10 times as much as aboveground lines–$1.5 to $3 million per mile compared with $285,000 to $800,000 per mile for above ground lines.
Variable costs The major variable costs are for maintenance and repair. Underground lines are more difficult to maintain or repair. The major direct cost to consumers is the cost of being without electricity. Ultimately all of the costs will be borne by the consumers.
Capacity Above ground cables have roughly 6 times as much capacity as underground lines.
Reliability While below ground lines are not 100% reliable, they are more reliable than overhead lines. Above ground power lines can be felled by wind, ice storms, falling trees and damaged by squirrels. Below ground power lines can be washed away or corroded along coastal areas due to storm surges. In Winter Park, Florida, where 80% of lines are underground, 98% of customers had power during Hurricane Milton.
Lifespan Aboveground lines have twice the lifetime, 70 years, compared with belowground lines.
Risks Aboveground lines can spark and cause fires. Pacific Gas & Electric paid $55 million after its power lines started a destructive brush fire. Also, sometimes power needs to be shut off to prevent any fires.
Aesthetics Clearly, belowground lines lead to a more pleasing appearance than overhead lines.
Classroom Discussion Questions
1. Does your community have underground or overhead wires or both?
2. What analysis could be done to make the decision between overhead or underground lines?