The Contribution of Airborne Data Collection on Electric Utility Vegetation Management

Utility forestry is the management of vegetation that could affect the transmission and distribution of electricity. The objective of a utility forestry program is to apply scientific knowledge to maintain reliable electric service. This is achieved by protecting electrical conductors from tree interference. Another goal must be recognizing the environmental benefits of trees and the public’s awareness of the value of trees.

A composite of information-based products and services to address strategic issues of the electric power transmission and distribution segment of the electric utility industry, as well as the associated support functions has been assembled by two industry vendors or our two companies. These entities, combined with other “team members”, together offer the electric utility industry a consistent, synergistic approach to gathering, analyzing, and reporting mission critical geographic information.

An airborne survey crew photographs transmission line right-of-way using highresolution digital framing cameras. Individual video frames can be indexed to the geographical location (longitude and latitude) of any target within the right-of-way. The specific location of each facility is captured as the individual digital frames are post processed.

Inventories of attributes are then collected using ground crews. Trained arborists inventory the vegetation and estimate the right-of-way maintenance workload affecting primary and secondary distribution lines and transmission lines in a project area. Data is collected using hand held (in some cases pen-based) computers.

Once all the data is centralized, a vegetation management plan is developed. This plan establishes guidelines for prioritizing, routing, budgeting, contracting, scheduling, and updating of the initial inventory.

Utility Forestry
The infamous Idaho “brown out” in August, 1996 positioned utility forestry in the national spotlight. A stretch of transmission line outside of Boise Idaho, came into contact with a singe Western Cedar tree causing a thirteen-state disaster.(1) The tree shorted out the transmission circuit for periods ranging from several minutes to about nine hours which, in turn, shorted its connecting circuits until over 7.5 million customers were without electricity. This nearly happened again only twelve days later. when a circuit bordering Boise contacted a tree and shorted out. The second time, however, an alert foreman cut electricity to Boise, preserving the interrnountain transmission grid while “turning out the lights” only in Boise.(2) These incidents have prompted utility organizations to monitor their vegetation under and adjacent to the transmission lines in a much more proactive manner.

Transmission right-of-ways are generally 300 – 400 foot wide corridors connecting power generation centers to electrical distribution sub-stations. The voltage of these lines range from 55 kilovolts to 500 kilovolts.(3) Due to the extreme electrical load these lines carry, clearance from the conductors are governed federally, at the state level, and by PUC (Public Utility Commission) organizations. Application of herbicides, mechanical mowing, and tree trimming maintain safe and legal clearance levels.(4) Aside from legal compliance, other motivators for utility operations to maintain transmission line clearance include un-interrupted service, safety, aesthetics, and the costs associated with energizing vegetation. Reliable service and safety leverage one another because the continuous flow of electricity presumes that the lines are safe for the public and those who manage them. Conversely, anytime that electricity is disrupted, it is reasonable to assume that an unsafe condition exists. Trees are often the cause of interrupted service and unsafe conditions because of the tendency for utility customers to expect the lines to be somewhat camouflaged by vegetation. When trees or areas of brush contact power lines, the utility company must absorb the cost of electricity lost through the line-tree-ground continuum.(5) In addition, fires started by tree-line contact can cost a utility millions of dollars each year, particularly in the Western United States where low rainfall during the summer months is common.