The landscape of reliability
Vegetation management programs keep power flowing safely to homes
By Megan McKoy-Noe
Trees may seem harmless on a calm, sunny day. But add a bit of wind or ice on a stormy night and those towering pillars may threaten your home’s electric supply. The last three major blackouts in the United States were triggered by tree-related transmission outages. It was a real wake up call when 50 million people were left in the dark after the last blackout in August 2003.
A great majority of our storm outages are related to trees contacting power lines. Regular trimming of trees and brush along power lines helps cut down on the number of everyday outages, multi-day long storm outages, as well as annoying blinks.
Electricity interruptions can occur when branches break and fall across power lines or when trees tumble onto power lines during major storms. But even a little wind can blow limbs against power lines causing short blinks on the line.
To fight these problems, electric co-ops wage a never-ending war. Vegetation management crews work year-round to clear growth away from power lines as a way of reducing potential outages and safety risks.
Vegetation management crews look for foliage growing under lines, overhanging branches, leaning or other types of “danger” trees that could pull down a power line if they fall, and trees that could grow into lines. As a rule of thumb, 25 feet of ground-to-sky clearance should be available on each side of utility poles to give power lines plenty of space.
Illinois electric cooperatives own 56,626 miles of distribution and transmission line. Maintaining the right of way along this vast area is a never-ending job. By the time crews finish clearing trees and brush from one area, it’s time to go back to the beginning to clear away new growth.
Despite the large scope of this job, vegetation management programs have met with widespread success. Electric co-ops are using new tools, arborist standards and even computers to create long-term and less expensive solutions.
The North American Electric Reliability Corporation (NERC), which oversees reliability of the transmission system that blankets the United States, most of Canada and one Mexican state, tracks bulk power supply-related outages. The group lists the period between July and September as “high-risk” for outages due to seasonal tree and shrub growth. NERC found that aggressive upkeep has led to a drop in vegetation problems. For the first time ever, no summertime transmission outages were reported last year.
“Managing vegetation along North America’s 350,000 miles of transmission lines is an ongoing challenge,” acknowledges Rick Sergel, NERC president & CEO. “I commend transmission owners and operators for this achievement, which clearly demonstrates the industry’s dedication to improving performance in this area.”
Making the Cut
Training and professional standards, along with new tools and procedures, have made this improvement possible.
In relatively short order many co-ops are turning vegetation management programs around by moving from strictly mechanical cutting to herbicide treatment programs. These new solutions create a right of way with low-growing vegetation by mowing and mechanical clearing the first year then following up the next year with targeted herbicides to stop the regrowth of trees and brush. Grasses and low growing food sources for wildlife are allowed to grow, thus choking out future tree growth under the line and creating a fire break, path for utility repairs and a fringe area for better wildlife habitat.
Wildlife organizations like the National Wild Turkey Federation have helped develop these vegetation management programs along with utilities and arborists. All wildlife species benefit and co-op maintenance cost can be reduced 25 to 40 percent while also reducing outages.
Another key to a co-op’s vegetation management success is good data management. A right of way audit identifies vegetation types, locations, growth rates, tree-related outage problems and other data. All right-of-way service orders, notification mailings, documentation and member approvals can be tracked using a co-op’s customer information system.
Kevin Louis, Manager of Engineering Applications for Rock Energy Cooperative, which serves several counties in northern Illinois and southern Wisconsin, has 16 years of experience working for electric cooperatives and dealing with vegetation management issues. He says computer tools, like geographic information systems (GIS), can help with vegetation management.
Louis says a GIS tracks tree-related outages, member complaints and special instructions, creates member notification mailings for specific areas, tracks recorded easements and provides a quick reference that helps limit miscommunication between a tree contractor, members and the co-op.
“I see technology becoming a bigger part of vegetation management,” says Louis. GIS systems can be excellent tools. Also, co-op employees can use GPS tracking of mowing, spraying and trimming.”
Derek Vannice, Director of the Utility Arborist Association, headquartered in Champaign, Ill., says the key change many utilities have made is having a trained utility arborist that can develop vegetation management specifications based on standards and best management practices.
Vannice says, “The International Society of Arboriculture, with the help of the Utility Arborist Association, has developed best management practices for utility pruning and integrated vegetation management.”
But Vannice says, member education is also critical. Cooperation between the member and the co-op can also help make improvements in vegetation management, he says.
While trees and branches remain the primary cause of outages, other offenders abound. Vehicles running into poles, animals getting too close
to pole-mount transformers or substation equipment can cause outages. Electrical components are also damaged by lightning or even drifting balloons.
Cooperatives, with a focus on keeping electricity reliable, have a number of programs geared toward reducing power interruptions. A 2009 study by the National Rural Electric Cooperative Association (NRECA), the Arlington, Va.-based service arm of the nation’s 900-plus consumer-owned, not-for-profit electric cooperatives, found 89 percent of cooperatives across the nation are aggressively improving tree trimming programs. More lightning arrestors are being added by 83 percent of co-ops, and another 82 percent are increasing field personnel patrols of distribution facilities to look for potential trouble spots. Animal guards, a relatively new outage prevention tool, are now being installed by 81 percent of co-ops.
Although a tree-lined street may sound ideal, trees planted too close to power lines will be trimmed to prevent power fluctuations and outages. So get your yard off to a good start by keeping utility poles in mind when planting trees.
In general, tall-growing trees or varieties boasting wide canopies shouldn’t be placed near utility poles. A local nursery can generally provide information outlining how tall and quickly a tree will grow.
Trees are a valued part of every yard’s landscaping, and with proper planning your trees can grow to their full potential without causing power line woes. Several guides are available for prospective planters; to learn more visit the Arbor Day Foundation at www.arborday.org.
Safety plays a big role in your cooperative’s right-of-way trimming practices. Children climbing trees could come into contact with a live wire if trees are too close to power lines. Notice any dead, dying or severely leaning trees near power lines in your area? Be sure to alert your electric co-op.
Sources: NRECA, National Arbor Day Foundation, North American Electric Reliability Corporation