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Resiliency

Resiliency/Hardening of Overhead Wood Pole Systems

Resiliency

Overhead systems that utilize wood poles must withstand a variety of environmental challenges from potential deterioration due to deacy and insects to hurricane-force winds, ice storms or wildfire.

Often after these extreme events, wood poles may come under criticism for their peformance, with calls to replace them with other "stronger" materials or to move the lines underground.

Such simplistic solutions ignore the economic benefits and inherent strengths of wood poles and the century-long record of solid performance in place. Advances in the smart grid and the coming wave of 5G will put more emphasis on overhead systems and wood poles have the capabilities to meet these new challenges, both structurally and economically.

Negative perceptions about wood poles often stem from the lack of investment in overhead systems. A 2017 infrastructure report card by the American Society of Civil Engineers gave the U.S. energy system a D+, citing an aging inventory that dates back to the 1950s. Osmose Utility Systems estimates the average age of wood poles in investor-owned utility systems is 33.9 years nationally.

More demanding environment

Meanwhile, the conditions wood poles face are becoming more demanding. The Center for Climate and Energy Solutions notes an increase in Category 4 and 5 hurricanes is predicted as a result of climate change. Wildfires are also increasing as summer tempertures rise and drought conditions persist in the West.

Despite such challenges, wood poles offer unique capabilities that can improve their reliability in place. Proper remediation, with proven preservatives and techniques, can extend the life of a wood pole at a fraction of the cost of installing a new pole. Wood poles offer a unique overload capacity that is recognized in national design standards, allowing wood poles to withstand extreme loads beyond their design capacity without failing.

Efforts such as vegetation management around overhead lines, as well as new methods to protect poles against wildfires, are improving reliability. And a variety of studies note that while moving lines underground marginally improves reliability, the costs are as much as 10-20 times more expensive compared to wood pole overhead line systems.

The following publications detail many aspects of reliability, including the considerations that should be reviewed when seeking to improve electrical grid reliability.

 

Wood Pole Resiliency

ServiceLife Technical Bulletin - Estimated Service Life of Wood Poles
Overview of the actual service life of wood poles in use, which is often much longer than what is assumed by utilities and others. Also includes review of the benefits of proper remediation in extending the service life of a pole.
8 pages, 03/16
PDF
TB_Overload NEW! Technical Bulletin - Unique Overload Capacity of Wood Poles
Reviews how natural variations and recognition of such variations in the National Electric Safety Code allow wood poles to have a much greater overload capacity in extreme weather events compared to poles made from alternative materials.
8 pages, 10/19
PDF
Equiv Technical Bulletin - "Wood Equivalent" Poles and the NESC
Discussion of issues in marketing thin walled steel poles, prestressed concrete poles, and fiber-reinforced polymer poles as "wood equivalent." Includes details on how the NESC applies different strength and load factors for each material, which means there can be no true "wood equivalent" poles.
8 pages, 05/17
PDF
CRS Weather-Related Power Outages and System Resiliancy
Congressional Research Service report on weather-related outages, the economic cost of such outages and recommendations on minimizing power disruptions.
18 pages, 08/12
PDF
TBHardening Technical Bulletin - Hardening of Utility Lines: Implications for Utility Pole Design and Use
Despite calls for "hardening" utility systems in response to storms, qualitative evaluations indicate current sytems perform as expected and potential actions to harden the system are expensive and offer questionable benefits.
8 pages, 11/07
PDF
PoleFire Performance of Utility Poles in Wildland Fires
Review of research on the performance of wood and steel utility poles in wildland fire hazard areas.
12 pages, 05/14
PDF