Xcel Energy's Northern states region transmission system consists of 7,500 miles (12,070 km) of lines throughout Minnesota, Wisconsin, North Dakota, South Dakota and Michigan — an area that encompasses approximately 85,000 acres (34,398 hectares). The utility's vegetation management department oversees and directs contracted vegetation management crews for routine clearing in this region to best ensure the safe and reliable operation of the transmission system. Contracted tree crews often work in remote areas that are inaccessible using traditional equipment and require manual, labor-intensive side-clearing.
Xcel Energy has a long history of using ground-based side-clearing methods that require a team of professionals skilled in navigating heavy equipment through remote and rough terrain. This includes the use of Jarraff-type equipment, brush mowing machines and herbicide-applying equipment. Together with Haverfield Aviation, Xcel Energy started a pilot program in August 2010 to test an aerial side-saw solution.
Xcel Energy's use of the aerial saw solution is part of an ongoing effort to look at new methods for improving efficiency and overall performance of its electric transmission system. The utility's goals are to protect its system, minimize environmental impact, perform work safely and efficiently, and maintain a positive relationship with landowners and the public.
With Xcel Energy focused on improving performance and cost, Haverfield's aerial saw solution cut through the challenges and set new standards for managing vegetation in the utility's more inaccessible corridors. Although several utilities have been using the aerial saw successfully for the past 20 years, this was Xcel Energy's first experience, so it started slow with one small project and led to several additional projects.
The Aerial Saw
The aerial saw consists of 10 circular, carbide-tipped blades, 2 ft (0.6 m) in diameter, which are suspended 120 ft (37 m) below the helicopter. A low-emission 28-hp Koehler 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 to be used depends on the height of the trees and the terrain.
The aerial saw clears the side of vegetation from the sky to the ground and can clear approximately 20 ft (6 m) of the right-of-way width at a pass. The aerial saw is particularly effective in mountainous terrain, swamps and environmentally sensitive areas.
Haverfield's safety and training department has a safety management system (SMS) that identifies hazards, and assesses and measures safety risks in an effort to mitigate and eliminate hazards. The system helps to track and evaluate safety management activities to ensure they are appropriate and effective. Haverfield constantly promotes safety to its employees through education and communication. Daily pre-job safety meetings were held each morning prior to doing any work.
The Pilot Program
The pilot program started with a 10-mile (16-1) trial on 69-kV H-frame structures, but it eventually encompassed numerous transmission lines, ranging from 69 kV to 345 kV, in and around southeast Minnesota and east-central Wisconsin. Xcel Energy also used the saw on a 1-mile (1.6-km) distribution line crossing hilly terrain with branches overhanging the conductors while maintaining the line energized.
Haverfield cleared the first line in 1 hour 20 minutes without causing any interruption in electrical service. Hand-clearing this line would have taken one of Xcel Energy's larger manual crews more than a month and had greater risk exposure.
The program's initial successes led to other opportunities in other parts of the service territory, including additional side-clearing conducted on a line crossing the Mississippi River. In this case, using the aerial side saw eliminated the need for boats, 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.
Another benefit of the saw is its ability to completely handle all clearing, eliminating the need for aerial lifts or all-terrain equipment. This is a significant benefit, especially when dealing with landowners who prefer heavy machinery not to be used on their property.
Xcel Energy is always cognizant of the environment and landowner concerns whenever engaging in vegetation management operations. Throughout the pilot program, landowners and communities were alerted ahead of time that the utility intended to use the helicopter and aerial saw. Haverfield and Xcel Energy's project planning included securing landing zones for the helicopter to refuel along the right-of-way. The upfront planning and communication was instrumental in minimizing customer concerns.
In some cases, only when necessary, a ground tree crew followed behind the helicopter to remove debris from roadways, waterways, fences, and landscaped and maintained areas. However, in most cases, the debris was left on the right-of-way to be mowed by follow-up crews or left to degrade on its own.
The feedback from landowners was largely favorable. They were amazed at the speed and efficiency of the operation. The few inquires and concerns raised by customers were quickly addressed by Haverfield and Xcel Energy.
A Successful Pilot
Almost 100 miles (161 km) of right-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.
Mountainous terrain or large bodies of water do not impede accessibility, which improves production.
The saw is nimble and has the ability to safely clear trees in relatively tight right-of-way corridors.
The aerial saw should be considered when working on projects with a limited window of time to complete the vegetation-clearing activities. The work can be accomplished in a shorter time frame than with traditional methods (one-fourth of the time less than mechanical equipment and one-twentieth of the time less than a manual crew).
In continuous areas, the aerial saw can provide significant cost savings, up to 80% when clearing non-accessible corridors requiring manual ground crews. The savings diminish when these areas are not continuous, requiring additional landing zones for refueling.
With the exception of the work being completed in a shorter time frame with the aerial saw, Xcel Energy did not see cost savings in areas where ground-based equipment can access the right-of-way. These are some additional items to consider:
Identify all distribution laterals that may be underbuilt on transmission structures and cross the corridor.
The cost of mobilization to get the helicopter saw to the operation region is built into project cost forecasts along with the cost of potential weather delays.
Determine the extent of proactive notification to affected residents, local units of government and local media outlets.
Existing line-clearance contractors should be involved in the project, as they likely will be involved in providing ground work where needed.
Working additional lines, even if accessible, is cost competitive with other mechanical side-pruning equipment.
The helicopter saw reduces tree worker exposure risk in difficult terrain and the manual climbing of trees.
Going forward, Haverfield and Xcel Energy are considering the use of the aerial saw to complete other projects in and around the utility's service territory in the Midwest. In addition, Haverfield recently added a horizontal saw known as the tree topper to its aerial saw services. This saw is used to top 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. It can be used in conjunction with the side-clearing saw for maximum right-of-way clearing. It is all a matter of using the right tool in the right situation.
Brad Weidenfeller ([email protected]) supervises transmission vegetation management for Xcel Energy in its Northern states region. He is based in Maple Grove, Minnesota, U.S., and oversees more than 7,500 miles (12,070 km) of transmission lines.
Haverfield Aviation | www.haverfield.com
Jarraff | www.jarraff.com
Koehler | www.kohlerengines.com
Xcel Energy | xcelenergy.com