When Hurricane Ike made landfall in Galveston, Texas, U.S., on Sept. 13, 2008, its Category 2 winds extended 275 miles (443 km) from the center. Behind Andrew in 1992 and Katrina in 2005, Ike was the third-costliest U.S. hurricane of all time, causing more than 13 million businesses and homes to lose power.

Typically, distribution systems are not designed to survive major weather events like hurricanes, including direct damage from wind and storm surges, and indirect damage from falling trees and flying debris. Many are beginning to wonder whether it would be beneficial for utilities to harden their systems so that they incur less storm damage and have faster restoration times.

In December 2008, a few months after Hurricane Ike, the Public Utility Commission of Texas hired Quanta Technology to investigate the costs and benefits of a variety of potential storm-hardening projects. Part of this investigation included a utility survey on best practices for distribution hardening.

A Dozen Best Practices

Based on the overall survey results, a list of 12 best practices was assembled to ensure distribution hardening is pursued through a process that is cost effective, consistent, transparent and data driven. The full survey report discusses an additional six recommendations for utilities that would like to be more aggressive.

The best practices are organized into two stages. In the first stage, the best practices are either inexpensive or good practices regardless of hardening considerations. They are also relatively simple to implement. In addition to being potential quick wins, they set the foundation for more ambitious actions. The best practices in the second stage are designed to be implemented in the intermediate term and generally require more utility effort, investment and potential changes.

First-Stage Best Practices

The first-stage best practices are no-brainers:

• Pole test and treat

  Wood poles are susceptible to decay, causing a reduction in strength and a corresponding increase in failure probability during a major storm. As such, utilities should establish and maintain a test-and-treat cycle for wood poles. This program should focus on, but not necessarily be limited to, decay at the ground line since this is typically the failure point for distribution structures under wind loading and the part of the pole most susceptible to decay. The goals of the test-and-treat program are to ensure no pole has lost more than one-third of its original strength and no pole is likely to have lost more than one-third of its original strength before its next scheduled inspection. This program should ensure deficient poles are reinforced or replaced in a timely manner.

• Feeder inspections

  Second-Stage Best Practices

  Utilities should have a formal feeder inspection program that periodically examines feeders for problems that will likely lead to an outage during normal and/or storm conditions. At a minimum, all three-phase main feeder trunks should be inspected every five years, although more aggressive programs are encouraged. Inspectors should be trained to watch for specific issues such as broken crossarms, cracked insulators, pole-top decay and so forth. The feeder inspection program is separate from the test-and-treat program. Information from these inspections should be kept in a common database, facilitating the analyses of trends and backlog.

• Attachment audits

  Attachments are a source of wind loading on poles. Therefore, it is important that utilities have a good understanding of the number and size of third-party attachments on their distribution poles. Third-party attachment audits should occur, at a minimum, every five years for all three-phase main feeder trunks. The attachment audit can be combined with feeder inspections if desired. Processes should be in place to identify new attachments, to determine whether the new attachments have overloaded the distribution poles and to mitigate overloaded poles.

• Foreign-owned poles

  Hardening Road Map

  Not all utilities own all of the poles on which they have equipment. Major storms do not distinguish between pole ownership when inflicting damage. Electric utilities should try their best to ensure foreign-owned poles are in as good of shape as their own poles in terms of remaining strength and loading. The processes addressing foreign poles can vary widely, ranging from the electric utility performing all inspections and maintenance to the electric utility ensuring the foreign owner is doing an adequate job.

• Setting depths

  A strong pole is of no use if its foundation is insufficient. Therefore, each utility should develop standards and processes to ensure the foundation of a distribution pole will not fail before the pole. These standards should have setting depth tables for poles of different heights and classes and for different soil conditions. Tables also should be made for very strong poles, including non-wood poles, which may be used for hardening purposes. The standards should describe how a setting depth calculation should be performed when none of the tables apply.

• Loading calculations

  The ability of a distribution pole to withstand extreme loads, such as wind and ice, is a direct function of its loading. A utility should have systems and processes in place to ensure poles do not become overloaded after they are initially installed. At a minimum, this should include a loading assessment whenever an additional piece of equipment is placed on the pole, a loading assessment whenever a new attachment is discovered on the pole and mitigation actions as appropriate.