Underground vs Aboveground (Overhead) Power Distribution|
Article - November 13, 2017 By LarsonElectronics.com
Underground vs Aboveground (Overhead) Power Distribution
According to the Federal Energy Information Agency, less than 18 percent of power lines in the US are buried underground. When it comes to exposure to unpredictable weather, aboveground transmission lines are highly prone to damage from nearby trees, poles, homes and structures.
With over 40 percent of power outages in the US caused by tree branches (falling/broken or overgrown), why don’t cities move power distribution underground, like they do in commercial airports?
Find out below.
Underground Power Distribution (Pros, Cons and Construction)
The advantages of underground power distribution are straightforward. Taking up less space on the surface, buried lines promote spaciousness and freedom in congested cities. Such configurations also make sensitive lines less prone to damage caused by strong winds and ice. These factors help improve electrical reliability, resulting in fewer power outages.
To reduce in-ground corrosion, underground lines are typically up to five times thicker than overhead variants. Moreover, the components can be placed in a conduit for extra protection. During installation, workers must dig a deep and wide trench, measuring 16’x 9’. This part of the process can be costly and very time consuming, depending on other underground structures present in the area. Prior to installation, the soil must be tested to determine the type of protective materials used to reinforce power lines.
It’s undeniable that locations with underground lines experience less power outages (up to 20 percent less). However, the time it takes to repair the structures in the event of failure is up to 1.6 times longer, compared to aboveground lines. This is because overhead poles are more accessible, as workers are required to first locate the issue before digging deep into the ground (difficult to do in bad weather), when it comes to fixing underground lines. It’s important to clarify that such wiring configurations can be damaged by floods, humans (accidental digging/trenching) and lightning.
True Cost of Underground Power Distribution
Numerous utility companies around the country have explored the large-scale application of underground power lines. Based on published reports of the projects, most business don’t move forward with the installations due to the following reasons:
• Underground lines are extremely costly; around 5-10 times more than overhead wiring
• The lines have a shorter lifespan
• Replacement and maintenance costs are high
• Redundant lines are needed to streamline repairs
• Lines buried underground cannot be uprated
According to a 2003 report released by the North Carolina Natural Disaster Preparedness Task Force (titled The Feasibility of Placing Electric Distribution Facilities Underground), researchers estimated it would cost the state $41 billion to move overhead lines underground. Surprisingly, such projects would take 25 years to complete and would result in higher rates for local customers. The report was furnished after a crippling ice storm hit North Carolina in 2002.
One of the few cities to attempt the widespread implementation of underground power lines is Anaheim, California. The city is currently in the process of completing a 50-year project that involves moving overhead lines underground. Local officials estimate costs to be $3 million per mile of cables buried, of which will be covered through a four percent increase in monthly energy rates for local residents. By comparison, overhead lines cost roughly $138,000 per mile during installation.
To conclude, from a large-scale perspective, underground power distribution is impractical and too costly for cities to adopt. But there are some situations wherein the application of underground lines is viable, such as locations that are prone to strong winds and highly populated areas (school campuses, airports and more).