Monday, November 2, 2020

How to Reduce Storm Restoration Times? Design ‘Super’ Structures

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Grid operators at Dominion Energy have learned from experience that damaged utility poles are among the most detrimental impacts of severe weather. In 2011, the 1,776 poles damaged by Hurricane Irene took nine days to repair, leaving 1.2 million Dominion customers without power for part or all of that time. Hurricane Isabel in 2003 damaged more than 6,300 poles, interrupting electric service for 1.8 million customers for up to 15 days.

“Dominion Energy has a responsibility to keep businesses operational and support the communities we serve by providing reliable electric service,” said Jason Hawkins, manager of electric distribution standards at Dominion Energy. “Based on a review of data from previous major storms, we determined that there was a direct correlation between the number of poles broken during a storm and the total restoration time. We concluded that a new resiliency standard to reduce the number of broken poles would greatly improve overall restoration efforts and allow Dominion Energy to better meet the needs of our customers.”

When trees fall on power lines during severe weather, restoration times depend on which components break. Past research by EPRI has demonstrated that it can take 15–35 labor hours to replace a single pole, depending on the complexity of the structure. (A two-person crew working for eight hours is the equivalent of 16 labor hours.) Replacement of a crossarm takes an average of about six labor hours (see chart). In general, damage to pole-top components can be repaired much more quickly than damaged poles.

“If a pole breaks, crews have to transport a pole to the site and complete a great deal of work to set and erect the pole,” said EPRI Technical Leader Joe Potvin, who leads research on resilient designs for distribution systems. “If the pole remains intact after a storm, you’ve eliminated all that site work. To shorten storm restoration times, utilities can design poles so that the pole-top components break before the pole itself.”

At its Lenox, Massachusetts site, EPRI built an outdoor facility that enables researchers to simulate tree strikes on various distribution pole designs. For each utility participating in the research, EPRI builds two structures according to the utility’s unique design and then interconnects the poles with unenergized power lines. The tree strike is simulated by dropping a large wooden pole on one of the spans (see video). If a pole breaks, the team makes design changes aimed at keeping the pole intact. Modified structures are retested, and additional adjustments are made to improve the structure’s resiliency.

“When we simulate tree falls, we observe how the pole system fails and document the order of events—component A breaks before component B which breaks before component C,” said Potvin.

Dominion Energy is one of the 15 utilities from the U.S., Europe, and Canada participating in the research. In 2019, EPRI simulated a tree fall with a structure built according to Dominion’s original design, and the pole broke. Based on the test results, Dominion designed a new structure with a wider pole diameter and a crossarm made of fiberglass instead of wood. When the modified design was subjected to a simulated tree fall, the pole did not break. Dominion is using the new design as the basis for its pole resiliency standard and is building new distribution structures according to that standard.

“Our modified design was better in theory, but there was a degree of uncertainty,” said Jason Beck, distribution standards technical specialist at Dominion Energy. “Partnering with EPRI gave Dominion Energy the opportunity to test and perfect our new design—and demonstrate that it did not result in broken poles. Using the videos from the EPRI tests, we were able to clearly communicate the results to internal stakeholders and gain their buy-in. In March, the Virginia State Corporation Commission approved the first three years of our ten-year grid hardening program, which allows us to use the new pole standard to upgrade structures in areas with frequent, long-duration outages.”

In late 2019, more than 20 utility experts convened at EPRI’s Lenox facility to share and discuss the industrywide results. At the end of 2020, EPRI plans to publish a comprehensive report on the research.

Key EPRI Technical Experts:

Joe Potvin, Drew McGuire
For more information, contact techexpert@eprijournal.com.

Technology Transfer Awards for Improving Resiliency of Distribution Pole Designs

Several utilities won EPRI Technology Transfer Awards for submitting their distribution pole designs for full-scale testing at EPRI’s Lenox, Massachusetts facility and then making design changes based on the results. The awardees were American Electric Power (AEP), BC Hydro, Central Hudson Gas & Electric, Dominion Energy Virginia, DTE Electric Company, Duke Energy, Electricity Supply Board, FirstEnergy, Georgia Power Company, Hydro One Networks, National Grid, and Xcel Energy Services.


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