Vegetation Management Whitepaper
Following the 2003 Northeast Blackout, the North American Electric Reliability Corp. (NERC) and the Federal Energy Regulatory Commission (FERC) responded with a new industry standard for managing trees and other plants within transmission right of ways (ROWs). That standard has recently been updated, with some significant changes.
The first Vegetation Management Reliability Standard (FAC-003-1) was released and became effective in early 2006. It required owners of transmission lines (200kV and above) to establish and maintain enough clearance between trees and transmission lines to prevent flashovers that could cause power outages.
The standard seemed to work well. For example, there have been countless thousands of vegetation-related distribution line outages since 2006, most commonly the result of trees or limbs falling onto distribution lines during storms (tornados, hurricanes, wind storms, blizzards, ice storms, etc.). Of course, the Federal Power Act has no jurisdiction over these local distribution lines. Such regulation occurs at the individual state level.
However, during that same time period, there have been few instances of outages resulting from direct vegetation contact or flashover with the transmission lines that were covered by FAC-003-1. One tribute to the effectiveness of the standard is how well transmission lines held up after Hurricane Sandy.
In addition, when vegetation-transmission line contact or flashover did occur, hefty fines were imposed. In 2010, for example, the Tennessee Valley Authority (TVA) received a $175,000 fine when an interruption was caused by a willow tree that had grown from seven feet tall to 37 feet tall in a three- year period. The tree grew to within 10 feet of a 40- foot high 500,000 volt line in Alabama, and caused an outage as a result of a flashover. TVA was fined even though no interruption of service resulted.
In December 2011, NERC submitted a revised standard proposal to FERC. On March 21, 2013, FERC issued a final rule approving NERC’s revised vegetation management standard (FAC-003-2). The rule went into effect on May 28, 2013.
While similar in many ways to FAC-003-1, the revised standard has three significant revisions.
The first is that it not only covers transmission lines 200kV and higher, but also those under 200kV, if those lines could impact bulk power system reliability – that is, transmission lines that are an element of the Interconnection Reliability Operating Limit (IROL) or an element of a Major Western Electric Coordinating Council (WECC) Transfer Path.
The second is that there is now a “zero tolerance” approach to vegetation management, which requires transmission line owners to prevent vegetation encroachment within the minimum vegetation clearance distance (MVCD), regardless of whether the encroachment results in a sustained outage. However, encroachments beyond the owner’s control, such as natural disasters or certain animal or human activity (other than the activity of the transmission line owner’s employees or contractors) are exempt from this requirement.
“One of the first fines that came down was $80,000 for a kudzu vine that crawled up a guy wire, which was inside the clearance zone,” said Paul Beaulieu, Manager, Transmission and Substation Engineering, for Finley Engineering, and who became a member of NERC’s Vegetation Management Standard Drafting Team in 2005. “Even though the kudzu vine couldn’t trip the wire, because it burns off, it was still considered vegetation in the zone, so there was no leniency.”
The third is that owners are now required to conduct annual inspections of all transmission lines subject to the reliability standard. Furthermore, owners are required to complete 100 percent of their annual vegetation management work plans. In addition, the annual inspection rule also requires that no more than 18 months pass between inspections.
Besides these three major changes, the new standard has attempted to provide additional clarifications. “What we did was try to take some of the ambiguity out,” said Beaulieu. “For example, we created an equation to try to define the clearance to the wire based on some kind of science. Before, this was utility-defined. That is, as long as you were compliant with what you defined, you were OK. However, this meant that there was no consistency between utilities as to what constituted adequate clearance.”
One other significant change for utilities resulting from the revised standard, as Beaulieu sees it, is that it requires a lot more documentation. “You need to be able to prove that you are actually doing what you say you are doing,” he said.
Specific documentation of your inspections will become more important. For example, you need to have a written inspection program, and you need to have documentation that you actually inspected what you said you inspected. You also need to be able to prove, via documentation, the quality of your inspections. “For example, you need documentation related to who trains your inspectors, and documentation related to how these inspectors know that what they saw was in compliance.” The remaining portion of documentation relates to execution – maintaining the trees to stay within the clearances.
“The main key to success to comply with the revised standard is to create a plan, and work far enough ahead of your plan to keep in front of it,” he said. “Then, after you execute the plan, be sure that you document what you have done.”
According to Beaulieu, the matrices within the revised standard are set up for some of the fines to be huge. “Some of them are so large that you could be bankrupt if you’re not diligent in what you do,” he said.