As wildfire and extreme weather events increase, utilities are upgrading their electrical systems in an effort to become more resilient against these threats. This process—known as system hardening—benefits customers and the environment by improving grid safety and reliability.
When making a system hardening decision, a key question typically arises: should we keep overhead lines or transition them underground? While the cost to underground distribution lines is typically higher than updating existing overhead lines, there are a number of other factors unique to system hardening that impact the outcome of this decision more than cost alone. Though not an exhaustive list, the following are some of the things utilities in high fire-risk areas should consider when deciding whether to update overhead infrastructure or move distribution lines underground.
FAA Height Restrictions
Engineering design criteria often dictates that replacement poles are taller than existing poles. If the planned pole replacements are within a Federal Aviation Administration (FAA) jurisdiction, there may be structural height restrictions. If this requirement conflicts with the engineering design for new overhead structures, a utility may make the decision to underground the line throughout jurisdictional airspace.
Scenic Areas
Most national, state and local scenic areas have strict regulations for development. Often, these policies are intended to protect the scenery by considering the infrastructure’s visual impact, making it challenging to acquire the necessary permits for overhead lines. Often, to obtain necessary permits in these spaces, it may be advantageous to underground a project through a scenic area.
Waterways and Habitat
Many counties—especially in Oregon—have strict development requirements to protect water-related areas such as riparian zones, floodplains and floodways. The protections include efforts made to modify existing distribution lines. Riparian zones may be impacted by vegetation clearing for either overhead reconductoring or installation of new underground lines. Consequently, it is important to carefully review local development codes, as they may impact permitting costs and project schedules.
Additionally, ground disturbance in environmentally-sensitive areas—wetlands, endangered species habitat and sensitive cultural resource areas, for example—may cause constraints that make undergrounding the line less feasible.
Public Agency Directives
Public agencies may have specific requirements for utility projects that can inform the decision to underground or overhead a system hardening project. For example, a state transportation department may have revised and updated design standards after an existing distribution pole was constructed. The revised standards may prohibit removing and/or replacing a pole in the same location along the highway. In some cases, these highway design standards have been the sole factor that determines whether to convert overhead distribution lines to underground lines along the state highway.
Right-of-Way and Easement Limitations
Typically, right-of-way agreements specify the width of an easement and the types of utility activities allowed within it. If an existing private easement only allows maintenance on an overhead line, then converting an overhead line to underground may require a new easement with the landowner.
On public lands—such as lands owned by the U.S. Forest Service or the Bureau of Land Management—use agreements between the utility and agency need to be renewed at regular intervals. If a utility plans to transition an overhead line underground, it is important to verify that the existing use agreement covers underground lines. If not, the use agreement will require modification. Similarly, if reconductoring is planned in an area with an expired use agreement, securing an agreement renewal will likely cause delays.
Extreme Weather
In areas where high winds and/or extreme cold conditions are present, undergrounding lines may minimize the risk of downed lines or disrupted service and allow year-round maintenance access. Areas that may experience significant ice loading or are snow-covered during the winter may consider undergrounding a line as an essential method for meeting operational requirements.
Community
Public sentiment—especially in residential communities—generally supports undergrounding distribution lines. In some communities, ordinances require that new distribution lines are installed underground for aesthetics and to minimize risks of service interruption from wildfires.
Even when overhead lines are being reconductored, utilities may face additional landowner requests, such as increased tree trimming or relocation of utility poles.
Physical Constraints
Soil type and topography are common considerations when deciding between overhead and underground solutions. These constraints can impact accessibility for maintenance and construction. In rocky terrain, undergrounding may not be cost-effective or feasible. While it is possible to underground lines in steep terrain, level surfaces are required for staging the drilling equipment.
Lack of access in remote areas can be a primary motivator to underground a line, whereas overhead is the common approach in rural areas where access is good and vegetation clearing is feasible.
Procurement
Recently, procuring project materials has proved challenging. On some projects, poles and equipment have been ordered up to a year in advance. On other projects, the inability to procure covered conductor and long lead times for poles have driven decisions to underground lines. Depending on the inventory needed, underground projects have also been negatively impacted by the lack of available materials.
A Collaborative Approach
The potential factors that may influence a decision to overhead or underground a distribution line for wildfire system hardening purposes are varied. It is essential to get input from multiple departments within a utility to make an informed decision. From the land department to construction and engineering, from environmental to community relations and procurement, each role brings a unique perspective and focus to the discussion.
Understanding the key drivers that influence the decision to overhead or underground a line for distribution system hardening can help inform the discussion. Considering each project’s unique constraints and working collaboratively to analyze the options will lead to more successful projects.
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