|A Haverfield helicopter prepares to lift a side trimmer saw. Note the row of 10 2-foot-diameter, carbon-tipped saw blades.|
BY DAVE PASKOWSKI, HAVERFIELD AVIATION INC.
Vegetation management is critical in preventing and minimizing electric power outages. Tree contact with power transmission lines is a leading cause of power outages.
This is what happened in 2003 when trees touched a transmission line and caused the line to switch off. Within two hours, a cascade of failures in the grid resulted in the largest blackout in U.S. history. More than 50 million people were without power in the Northeast and Canada. After that blackout, the Federal Energy Regulatory Commission (FERC) tasked the North American Electric Reliability Corp. (NERC) with developing standards to protect the power grid and prevent outages. FAC-003-1, the Transmission Vegetation Management Program, was adopted in 2006. The rule addresses vegetation management including tree trimming in transmission line rights of way, where those lines are 200 kV and above, as well as lower-voltage lines designated as interconnection reliability operating limit (IROL) lines.
Traditional vegetation management involves ground-based tree crews. The work often is done in remote areas that are inaccessible using traditional equipment and require manual, labor-intensive side clearing. This method requires a team of professionals skilled in navigating heavy equipment through rough terrain. Crews climb trees along the rights of way and drop limbs while slowly, methodically moving along their assigned routes. In a good season, a crew can clear some 40 miles of vegetation.
An alternative to the traditional ground-based method is aerial vegetation management. The aerial option protects power systems, minimizes environmental impact and performs work safely and efficiently with fewer workers and less equipment. This results in significant operational cost savings while maintaining positive relationships with landowners and the public.
Haverfield Aviation Inc. introduced aerial vegetation management services in 2008. After identifying a need for more efficient vegetation management, employees developed equipment designed for helicopters. The result is an aerial side-cutting saw that consists of 10 circular, carbide-tipped blades-2 feet in diameter-suspended 120 feet below the helicopter. A low-emission engine drives the saw, which a pilot operates from the cockpit. The length of the aerial saw can be increased or decreased by adding or subtracting sections of aluminum poles. The length depends on the height of the trees and the terrain.
|A Haverfield helicopter trims a stretch of right of way with a side trimmer saw. Using the aerial saw, a pilot can clear a line in about one hour-what it would take a ground crew up to a month to finish.|
The aerial saw clears the side of vegetation from the sky to the ground and can clear some 20 feet of the right of way width at a single pass. The aerial saw is particularly effective in mountainous terrain, swamps and environmentally sensitive areas.
Another benefit of the saw is its ability to handle all clearing, which eliminates the need for aerial lifts or all-terrain equipment. This is a significant benefit when dealing with landowners who prefer heavy machinery not be used on their property.
A pilot program completed for Xcel Energy’s Northern States Power Co. transmission system provides real-life benefits of aerial side cutting. The pilot program began with a 10-mile trial on 69-kV H-frame structures, eventually encompassing additional transmission lines, ranging from 69 kV to 345 kV. Also, the saw was used on a 1-mile energized distribution line that crosses hilly terrain with branches that overhang the conductors.
The first line was cleared in 1 hour, 20 minutes without interrupting electrical service. Hand clearing this line would have taken a large manual crew more than a month and at a greater risk exposure.
The program included additional side clearing on a line that crosses the Mississippi River. In this case, using the aerial side saw eliminated the need for expensive barges and significantly reduced the time and cost to complete the work. Using traditional methods, this section of work would have taken manual crews weeks to complete at close to 10 times the cost.
|A Haverfield helicopter prepares to lift a horizontal tree-topper saw. The shroud conceals two 3-foot-diameter, carbide-tipped blades. Under normal circumstances, the tree-topper saw can top both sides of a power line at a rate of 1 mph.|
In some cases when necessary, a ground crew followed the helicopter to remove debris from roadways, waterways, fences and landscaped and maintained areas. In most cases, however, the debris was left on the rights of way to be mowed by follow-up crews or left to degrade on its own.
Nearly 100 miles of rights of way edge had been cleared by the end of the nine-week pilot program with positive benefits:
- There was virtually no physical footprint made by the equipment, which reduces or eliminates the need for permits in some cases; and
- Mountainous terrain or large bodies of water do not impede accessibility, which improves production.
Haverfield’s latest aerial saw innovation is a horizontal saw known as the tree topper. This signature addition to the market tops trees along the right of way edge to prepare them for takedowns. The tree topper also is used to mitigate hazard trees identified through vegetation patrols and LiDAR surveys. It can be used in conjunction with the side-clearing saw for maximum right of way clearing.
The horizontal saw consists of two 3-foot-diameter, carbide-tipped blades. Like the vertical saw, it is suspended by tubular sections from the helicopter. The tree topper also can be used to reclaim rights of way for tree removals. Used for cutting treetops next to high-voltage lines, the tree topper cuts trees short enough to keep them from hitting power lines if they fall. As with the vertical saw, the tree topper is driven by its own motor and operated by the helicopter pilot. The cutting line is determined by the height of the power line as reference. Topping trees with the helicopter and horizontal saw strongly reduces the need for manually climbing trees. Under normal circumstances, the tree topper saw can top both sides of a power line at a rate of 1 mph.
|A Haverfield helicopter takes off to top trees next to high-voltage lines. Topping trees with a helicopter greatly reduces the need for climbing trees.|
The tree topper is particularly effective in addressing diseased and dying trees. Since the accidental introduction of the emerald ash borer to the United States, 50 to 100 million ash trees have been killed across 14 states. It is estimated that most of the 1.5 billion ash trees throughout North America will be affected. With millions of dead standing trees in Michigan, Ohio, Indiana and Illinois and the disease’s spreading to Wisconsin, Minnesota, Iowa, Pennsylvania and Maryland, tree removal will pose a large problem for utilities in the hard-hit areas.
Whether it is the side trimmer, tree topper or both, the aerial saw option should be considered when utilities are working on projects with limited windows to complete the vegetation-clearing activities. The work can be accomplished in a shorter time than with traditional methods (one-fourth of the time less than mechanical equipment and one-20th of the time less than a manual crew). In continuous areas, the aerial saw can provide cost savings up to 80 percent when clearing nonaccessible corridors’ requiring manual ground crews. It is all a matter of using the right tool in the right situation.
Dave Paskowski is aerial saw program manager at Haverfield Aviation Inc. Visit http://haverfield.com for more infomation.