Managing vegetation in and along our rights-of-way (ROW) underpins our strategy for maintaining transmission and distribution system reliability.
Vegetation growing into and trees falling onto power lines are the major cause of power outages which is why managing vegetation in and along our rights-of-way (ROW) is part of our strategy for maintaining system reliability.
Vegetation-related outages and equipment failures are among the biggest challenges to AEP’s service reliability. AEP manages the trees and vegetation around power lines using a combination of performance-based (such as targeting low-performing circuits) and cycle-based maintenance strategies. Maintaining a regular tree-trimming cycle is a significant expense that directly affects customer bills and satisfaction.
During the past five years, AEP has spent more than $1.64 billion in vegetation management, including $343 million in 2017. The issue of reliability has prompted several states to consider or implement shorter intervals between tree trimming programs.
Trees from outside of the traditional ROW are a major threat to reliability. When a heavy tree hits a power line, the poles and wires are generally broken, extending the time it takes to restore service to customers. In 2017, falling trees accounted for approximately 22 percent of the total AEP customer minutes of interruption and, over the past five years, we have seen the number of these outages increase by 15 percent.
The increase is primarily driven by environmental issues that are weakening or killing trees. For example, the ash tree population in Ohio has been decimated by the emerald ash borer insect. Dead ash trees have been a contributing factor to a 65 percent increase in Ohio’s outages due to trees from outside the ROW over the past five years. To help control and prevent the damage that trees outside of the ROW can cause, we work to identify and remove trees that are dead, dying or leaning precipitously toward our lines. In 2017, approximately $75.8 million was dedicated to tree removals; and in the mountains of West Virginia, an additional $5.8 million was dedicated to widening “up-the-hill” ROWs in targeted areas above transmission lines.
We are always looking for more efficient, safer, cost-effective and environmentally friendly ways of managing vegetation in our ROWs. The terrain in some parts of our service territory is particularly challenging because it is so mountainous. Appalachian Power regularly uses helicopter contractors for aerial spraying of herbicides, inspections and tree trimming using an aerial saw. In the rugged mountain terrain of McDowell County, W.Va., helicopter use not only saves the time of driving from ridge to ridge, it’s a lot safer for workers because many of the older structures put our employees who must climb them at risk. In addition, helicopter use impacts the environment a lot less because it eliminates the need to build access roads to each structure in the mountains.
Severe weather events have made it clear that electric distribution and transmission systems need to be made more resistant to damage from vegetation during major storms. Over the past several years, our operating companies have received approvals from state commissions in West Virginia and Kentucky to implement more aggressive vegetation management programs, moving tree-trimming and other vegetation management to cycle-based programs. Vegetation management cycles have already been established in Oklahoma and Ohio.
2017 marked the third year of cycle-trimming vegetation management in West Virginia, where vegetation growing into and trees falling onto power lines are the major cause of power outages. The improvement to reliability is significant with the number of outages related to vegetation in the rights-of-way down by 32 percent over the past five years. In addition, the frequency of outages is down 40 percent, and the customer minutes of interruption are 43 percent lower. By the end of 2017, the new cycle program had been applied to more than 12,300 miles of distribution and transmission lines.