The landscape of

reliability

Vegetation management programs keep your power flowing safely

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.

“A great majority of our storm outages are related to trees contacting power lines,” comments Ken Guffey, director of safety and loss control for the Oklahoma Association of Electric Cooperatives. “Regular trimming of trees and brush along power lines helps cut down on the number of 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. When strong winds blow, limbs growing too close to power lines may sway and touch wires. These momentary power disruptions (commonly called “blinks” or ‘blips”) aren’t just mild annoyances—they can damage computers and other sensitive electronic equipment and leave digital clocks flashing. And then there’s arcing—when electricity uses a nearby tree as a path to the ground. That action poses hazards to anyone in the vicinity and could spark a fire.
 To fight these potential problems, utilities wage a never-ending war. [Vegetation management/tree trimming/right-of-way] crews work, in some cases, year-round to clear growth away from power lines as a way of reducing potential outages and safety risks.

“Your local co-ops are committed to providing safe, reliable, and affordable power, and our [Vegetation management/tree trimming/right-of-way] program is key to fulfilling that promise,” stresses Guffey

[Vegetation management/tree trimming/right-of-way] 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.

“This job never ends,” explains Guffey. “By the time our crews finish clearing trees and brush from hundreds or even thousands of miles of lines, it’s time to go back to the beginning to clear away new growth.”

Vegetation management programs have met with widespread success. 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.

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
Typically, a utility will not remove trees. Instead, errant limbs and branches too close to power lines are trimmed away.
“The Tree Care Industry Association [TCIA, formerly the National Arborist Association] receives a lot of calls from homeowners complaining that their utility company ‘drastically’ cut trees near power lines,” shares Tchukki Andersen, TCIA staff arborist.

Your co-op respects your property, and decides how to trim trees based on the amount of clearance needed around wires, voltage coursing through lines, the tree’s growth rate and the right-of-way maintenance cycle (how frequently trimming along the line is performed).  Most lineworkers and crews hired to perform [vegetation management/tree trimming/right-of-way maintenance] treat trees with care, often following TCIA guidelines.
“When evaluating the quality of such activities, consider that a utility’s primary objective is to prevent outages as well as electrical hazards,” explains Andersen.

Members who are distraught by tree trimming practices should weigh their frustrations against the alternative: potentially unreliable electric service and the possibility of prolonged outages.
For long-standing trees that have grown too close to overhead lines, several trimming options are employed. A V-cut prunes branches back toward the center of the tree’s crown, basically carving a V-shape through the middle to provide proper line clearance.

If limbs grow too close to lines on one side of a tree, side trimming takes place—branches on the entire side are removed. Finally, the notch method clips limbs on one side of a tree from the top to a safe area underneath, leaving a canopy that will not cause any problems.

If you want to remove a tree near a power line, your co-op will work with you. Contact the office before tackling the project for more information.

Branching Out
While trees and branches remain the primary cause of outages, other offenders abound—vehicles running into poles or animals getting too close to pole-mount transformers or equipment in substations. Electrical components can also be damaged by lightning and even drifting balloons.

Cooperatives, with a focus on keep electricity reliable, have a number of programs geared towards reducing power interruptions. A 2009 study by the National Rural Electric Cooperative Association (NRECA), the service arm of the nation’s 900-plus consumer-owned, not-for-profit electric cooperatives, found 89 percent of cooperatives across the nation operate aggressive tree trimming programs. Lightning arrestors are used by 83 percent of co-ops, and another 82 percent have field personnel patrol distribution facilities to look for potential trouble spots. Animal guards, mainly used to protect against squirrels, are installed by 81 percent of co-ops.

Your Part
 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—keep 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 utility’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 local electric cooperative. And don’t worry—if high winds or heavy layers of ice bring down trees and power lines near your home, local co-ops have line crews on call 24 hours a day, seven days a week to respond.

            
Sources: NRECA, National Arbor Day Foundation, North American Electric Reliability Corporation

Megan McKoy-Noe writes on consumer and cooperative affairs for the National Rural Electric Cooperative Association, the Arlington, Va.-based service arm of the nation’s 900-plus consumer-owned, not-for-profit electric cooperatives.