The Northeast Blackout of 2003 affected 50 million customers throughout nine states and Canada. Shortly following this event, the United States enacted the Energy Policy Act of 2005, which required mandatory reliability standards. The reliability standard FAC-003, specifically for prevention of vegetation-related outages of major transmission lines by maintaining prescribed clearances to conductors, took effect in April 2006. In turn, electric utilities took a closer look at their vegetation management programs.

PPL Electric Utilities used to trim trees along transmission rights-of-way (ROW) on an as-needed basis, but two years ago, the utility took a more proactive, yet more aggressive vegetation management approach on its high-voltage transmission lines. As such, it needed to better manage the program to ensure reliability and compliance with the stricter federal standards while meeting safety, efficiency and customer service expectations. The utility manages a 10,000-sq-mile area across central and eastern Pennsylvania and serves 1.4 million customers.

Four years ago, the utility partnered with GeoDigital Inc. to perform a light detection and ranging (LiDAR) scan of its major transmission lines and vegetation clearances. The utility was then able to identify areas with clearance issues and rectify those problem areas before they become violations.

The LiDAR technology determines the distance from the conductors to the ground and quantifies the distance from the vegetation to the conductors. As the line carries more current, it heats up, expands and then sags. Like other utilities, PPL Electric aims to measure its system for clearance requirements at maximum sag. By using the LiDAR technology, the company was able to meet clearance compliance requirements and then plan and prioritize work.

Through the use of LiDAR, the company discovered a significant number of places where clearances were not sufficient. The utility then called upon its professional foresters to manage the work, and qualified tree contractors Asplundh Tree Expert and Penn Line Services to complete the work.

Shifting Direction

Following the 2009 LiDAR scan, PPL Electric shifted from a selective trimming program to a ROW management approach to improve reliability and meet clearance requirements. The wire-zone/border-zone approach is a long-term sustainable risk management strategy that conforms with industry best practices.

PPL Electric's wire-zone/border-zone approach calls for the utility to clear under the transmission lines 10 ft out on each side from the outer most conductor. The vegetation in the wire zone is generally limited to grasses, ferns and herbaceous plants. The border zone extends from the edge of the wire zone to the outer limits of the ROW width. Certain trees and shrubs are allowed, depending on their growth and height characteristics. In the border zone, smaller trees like dogwoods and cedars are permitted to remain.

In some cases, border zones along with wire zones are completely cleared because of the quantity of noncompatible species. The wire-zone/border-zone approach promotes native, compatible species underneath and adjacent to the transmission line conductors. This approach creates a diverse habitat area for birds and other wildlife, distinguishing between forest area, shrub area and grasslands.

Planning and Performing Work

Before clearing trees and applying herbicide, PPL Electric assembled an experienced team including project managers, professional foresters, corporate communications and contractors to lay out a plan for better managing the utility's ROW. This team focused on prioritizing and planning field activities, scheduling work with the contractors, communications and quality control.

The transmission vegetation management program was prioritized to shift to the wire-zone/border-zone approach initially for the 230-kV and 500-kV lines in the bulk power network and subsequently for the 138-kV lines. The utility sought to complete work under new clearance guidelines for the higher-voltage transmission system — about 1,351 miles of ROW — over three years, then doing an additional 300 miles of the 138-kV system during a later transition period.

In an effort to stay organized, PPL Electric's trained foresters and skilled analyst map out all the work that needs to be done on an annual basis. The preplanning of work takes place in the third quarter of the year prior to when the work will be done. The utility mapped out each line and assigned each unit a cost estimate, estimated start time and completion time.

Once the company had its annual work plan in place and implemented “multiple touch” communications with property owners, it became easier for the field crews to proceed with the schedule. The qualified contractors cleared the vegetation using mechanized and/or manual hand cutting to establish the zones. They cleared out all the vegetation so nothing incompatible was growing within the wire or border zones.

A team from either Asplundh Tree Expert or Penn Line Services came in with large mechanical equipment such as a Hydro-Ax from Prentice Forestry. This machine features knives, hammers and axes at the front of its rotary blades and can be used to clear a ROW.

In almost all cases, PPL has easement grants with the property owners to allow maintenance of the utility ROW for the benefit of the utility's transmission network. Based on the terrain, the field crews decide what is the best approach. For example, if they need to clear tall trees, then they use long-armed mechanical equipment such as the Jarraff, a telescopic pole with a buzz saw on the end from Jarraff Industries. In addition, they use heavy-duty mowers and feller bunchers to perform work on a given line. A feller buncher is a motorized vehicle with an attachment that can rapidly cut, gather and control several trees before felling them.

After PPL Electric's contracting crews have cleared the trees, then the company's foresters visit the job site. The foresters are certified and trained, they know vegetation species, and they interact with property owners. As such, they perform a final quality inspection to make sure everything is done to meet specifications and standards. At PPL Electric Utilities, all planned work scope is thoroughly inspected.

Applying Herbicide

After they remove incompatible vegetation in the ROW, the crews then begin one of the most important parts of a successful program — herbicide application.

Historically, PPL Electric used only a foliar or stump treatment or a basal application for its herbicide. For this project, however, PPL tried a new approach by using a cut stubble application. Immediately following the clearing of the trees and brush, the crews apply the herbicide. Before anything germinates, it allows the chemicals to penetrate and limit the start of growth of any woody vegetation such as trees. It doesn't restrict grasses and ferns. PPL Electric aims to achieve a 95% take rate with the herbicides, meaning only 5% of the woody vegetation remains.

The company has 11 different potential mixtures that can be used. Many years ago, herbicide mainly consisted of diesel oil and water, which would kill all vegetation in its path, but now utilities can use different products based on the specific species. For example, an aquatic herbicide can be used near water with no adverse impact to the aquatic environment.

Proper herbicide use is an important element to an integrated vegetation management program's long-term effectiveness. It requires the company foresters to be educated on the variety of herbicide options now available and different treatment methods. Additionally, it requires regular, ongoing training for the foresters and the licensed contractor personnel.

The vegetation management professionals try to match the herbicide with the type of environment they need to treat. The field crews then apply the herbicide with four-wheeling Radiarcs from Waldrum Specialties Inc. or Brown Brush Monitors from Brown Manufacturing. The drivers make a pass covering a 10-ft area. They also manually apply the herbicides by pulling hoses, which extend up to 1,000 ft from the truck's tank.

While the public is often fearful that the herbicide is being applied like crop dusters, in reality, it is only applied in a targeted fashion from the ground. The field professionals either apply the herbicide using handheld equipment with a specialized backpack they wear or motorized equipment.

A Dramatic Change in Course

Initially, the employees had some reservations about a significant change in PPL Electric's vegetation management program, after having used the selective management approach for the past 25-plus years. By soliciting feedback from everyone from field crews to top leadership, however, the utility was able to implement its plan for integrated vegetation management.

The field crews began implementing the project in the first quarter of 2010, and at this point, the company has completed maintenance of about 950 miles out of 1,651 miles. Through the wire-zone/border-zone approach, PPL Electric is taking control of its transmission vegetation management program and, in the process, is improving customer awareness and reliability.

The utility's customers are gaining an awareness of how the company needs to properly maintain its ROW. In turn, this improves the reliability on the electric transmission system and assures compliance with the federal reliability standards.

Like many utilities, PPL has invested substantial funds in vegetation management that is central to its overall preventive maintenance program. Within a relatively short period, the company is regaining control of the bulk power transmission paths while managing a high volume of public inquiries and experiencing few obstacles. Concurrently, the company maintains 28,000 miles of distribution power lines and getting ready to expand wire zone/border zone to the 138-kV system.

In essence, LiDAR points the way and ensures the company prioritizes its work effectively in advance and helps with quality control following work. A strong project management approach, along with close collaboration among vegetation management, environmental and several internal departments keeps the utility's program on track.


Phil Walnock (pjwalnock@pplweb.com) is the manager of vegetation management and its $35 million annual program for PPL Electric Utilities in Allentown, Pennsylvania. PPL Electric is one of five utility subsidiaries of PPL Corp.

Communication is Key to Success with Wire-Zone/Border-Zone Approach

Comprehensive public outreach with effective communications is vital to PPL Electric Utilities' wire-zone/border-zone approach. PPL prides itself on customer satisfaction with 17 awards from J.D. Power & Associates and strong community relationships. The company is also a Tree Line USA recognized utility, which is an annual honor for tree industry best practices in customer service, training, public education, conservation and community outreach.

Here are the steps PPL took to ensure a smooth transition from its past practice to an integrated vegetation management program.

  1. Set up a call center

    The utility works with an affiliated company to arrange for handling of telephone inquiries generated from its extensive public outreach, which includes letters, brochures, a dedicated website and in-person visits to customers and local officials. The company's professional foresters work to respond to customer questions within 24 hours.

  2. Discuss the benefits of the program

    The utility used Dow Chemical's Notify Your Neighbor training program to educate its vegetation management employees and contractors on effective ways to communicate to property owners about the work that needs to be done, why it is being done and the long-term benefits when completed. Similar “benefits-focused” messaging is regularly shared with other key audiences.

  3. Notify customers often and early

    Four to six weeks in advance of planned work, the utility sends a letter to property owners along a transmission line about what will be done and the reasons. Key messages, which can be found on PPL's website at www.pplweb.com/vegetation, focus on reliability, primary causes of the Northeast Blackout of 2003, the change in approach and continued environmental stewardship. Two to three weeks after the letters are sent, one of PPL's certified contractors personally notifies and educates property owners about the work to be done. The vegetation management professional then puts out flags to mark the edge of the utility easement and the species in the rights-of-way to identify what vegetation would be affected.

  4. Be prepared to deal with conflict

    Within 48 hours, PPL's contractors knock on the door at customer properties before doing the work. If a customer refuses to permit work to be done, then the contractor refers the issue to the company's forester. The forester personally visits the property to meet with the customer with copies of the utility easement in hand. The easement agreement serves as a grant between PPL and the property owner, and gives PPL broad rights to perform necessary work to maintain the electric transmission facilities. More often than not, the forester is able to resolve the situation on the spot. About 10% of customers scheduled to have work done on their property contact the call center with inquiries. About 4% to 5% require a callback from the forester and only 1% requires intervention from PPL's Office of General Counsel.

  5. Seek collaboration

    In 2010, PPL performed physical tree maintenance on the property of about 3,500 property owners along the transmission rights-of-way. To perform this work successfully, PPL not only conducted extensive outreach for property owners, but communicated in a timely manner to elected local, state and federal legislators and officials, as well as special interest groups. It also required a significant collaborative effort from many internal departments.

Companies mentioned:

Asplundh Tree Expert Co. www.asplundh.com

Brown Manufacturing Corp. www.brownmanufacturing.us

DuPont www.dupont.com

GeoDigital Inc. www.geodigital.com

Jarraff Industries Inc. www.jarraff.com

Penn Line www.pennline.com

PPL Electric Utilities www.pplelectric.com

Prentice www.prenticeforestry.com

Waldrum Specialties Inc. www.waldrumspecialties.com