|Before adopting lidar, PPL performed transmission rights-of-way inspections with the naked eye, helicopter, on foot or via mobile patrols through PPL’s bulk power system.|
by William Atkinson, Contributing Editor
“Tree contact with transmission lines is a leading cause of electric power outages and a common cause of past regional blackouts, including the August 2003 blackout that affected 50 million people in the Northeast United States and Canada,” according to the Federal Energy Regulatory Commission (FERC).
Since then, FERC has given the North American Electric Reliability Corp. (NERC) the responsibility to develop and enforce standards to ensure the reliability of the bulk power system, including the reliability standard, FAC-003-1, that addresses vegetation management covering tree trimming on rights-of-way.
Many utilities use lidar (light detection and ranging) to come into and remain in compliance with FAC-003-1. Lidar is an optical remote-sensing technology that measures properties of scattered light to find range, other information or a combination of them on a distant target. It uses laser beams usually from a helicopter to measure distances accurately from wires to potential obstructions-primarily trees. It then creates a map that displays the relative heights and positions of towers, power lines and trees. Lidar also can document compliance, which is important for utilities in being able to demonstrate FAC-003-1 compliance.
PPL Electric Utilities
PPL Electric Utilities in Allentown, Pa., was an early lidar adopter. PPL’s transmission and distribution (T&D) system spans some 40,000 miles (aerial, not including underground); about 33,000 miles are distribution, and a little less than 7,000 miles are transmission.
“When the NERC vegetation management regulation came out, we realized that we needed some sort of tool to make sure we were getting accurate data in order to be in compliance,” said Bill Klokis, PPL vegetation manager. “The NERC standard covers anything over 200 kilovolts in the bulk power system, and we have about 1,368 miles of 230 kilovolt and 500 kilovolt.”
Before adopting lidar, transmission right-of-way inspections were done with the naked eye via helicopter, foot or mobile patrols through the utility’s bulk power system, Klokis said.
PPL adopted Lidar technology in 2008.
“At first, we had some challenges,” Klokis said.
For example, the utility had to recalculate its line sags, results of the voltages going through the lines and air temperatures.
“The lines can get quite close to vegetation and even to the ground,” he said. “When we studied the information from our first lidar test run, we realized we had been calculating our sags incorrectly.”
PPL introduced a more accurate calculation called finite element calculation, which has improved sag calculation accuracy.
The utility has been happy with its lidar technology, Klokis said.
“The accuracy of lidar gives us a level of confidence and peace of mind that we are fully compliant with the NERC clearance standards,” Klokis said. “We have found that there is nothing else on the market that does this better.”
PPL likely will expand lidar to other lines, possibly as early as 2013, he said.
“We will probably begin using it on our 115-kilovolt and 138—kilovolt lines after we get those rights-of-way cleared,” Klokis said.
Northeast Utility System
Northeast Utility System in Hartford, Conn., also is satisfied with its lidar technology, said Anthony W. Johnson III, the utility’s manager of transmission vegetation management.
“We had a lot of vegetation in our rights-of-way, specifically a species called red cedar,” Johnson said. “With the inception of the NERC transmission system vegetation management standard, we started removing the red cedars that were in the rights-of-way en-masse.”
This strategy, however, upset some regulators who decided where the utility could place facilities, Johnson said. As a result, Northeast Utility System cut back on its red cedar removal.
“We could only remove about 50 percent of the population in any line or span during any maintenance year,” Johnson said.
The cutback left the utility exposed to possible violations of the NERC standard because of line sag situations, he said.
|Lidar helps PPL target where to remove trees that are getting too close to clearances.|
“Under all operating conditions of the lines, we wouldn’t know where the lines were in relation to the vegetation in the rights-of-way,” Johnson said.
Northeast employed lidar technology.
“After conducting the initial lidar surveys, we were able to take the information that we had gleaned from modeling our lines under all operating conditions and showing how close vegetation would be to those lines under those extreme conditions,” Johnson said.
This helped the utility target where to remove trees that were getting too close to violating NERC’s clearance standard. Using lidar, Northeast has met requirements of the standard and saved money by removing fewer trees.
Northeast is considering adopting geo-technologies such as geographic information system (GIS) and GPS to provide more management along transmission corridors. (GIS merges cartography, statistical analysis and database technology to capture, store, analyze, manage and present geographical data.)
“Right now we are paper-based, which means that we have to pull out plan and profile maps to find out what our easement widths are,” Johnson said. “We then have to pull out paper easements, which are stored at a different location in the company, to find out what our rights are.”
Then, the utility takes field measurements to determine whether vegetation is within its easements and property lines.
“Our monuments are still marked out in the field, but they are very difficult to locate,” Johnson said. “As a result, we never know based on where we are standing in a right-of-way where our easements and limits are.”
A geo-technology system that allows the utility to incorporate all this information into one field-acceptable unit will show workers spatially, especially on a geo-reference point, exactly where they are at any time.
“This will make it a lot easier for us to know what work needs to be done, when we are in certain areas that have restrictions or special conditions, and also what our easement boundaries are,” Johnson said.
Invasive Species Sometimes a Tree Trimming By-product
Whether utilities are aggressive in tree management or not, invasive species-all the way from vines and shrubs to trees-have taken over parts of the country in recent years and are playing havoc with transmission towers, distribution poles and lines. Adding to the problem is that with ever-increasing requirements to trim and cut trees along utility rights-of-way, the cleared rights-of-way have become more enticing breeding grounds for invasive species.
“By the early 1990s, we had gotten so good at removing tree species in our rights-of-way that we ended up with nothing but invasive shrub species,” said Anthony W. Johnson III, manager of Northeast Utility System’s transmission vegetation management.
As the utility cleared the trees, the rights-of-way filled up with lower-to-the-ground invasive species, he said.
“We ended up with such a massive growth of vegetation that we couldn’t drive or walk through it,” he said. The utility’s rights-of-way had become breeding grounds for these species because the shrubland birds that populated these areas ate berries from the invasive shrubs, then deposited the seeds along the rights-of-way, continuously propagating the shrubs.
“It got to the point where we couldn’t even see the vegetation that would eventually become problematic when it finally grew up above the dense, shrub-layer canopy. We couldn’t see them or get to them once we finally did see them.”
The utility realized that most of the shrub species were state-listed invasive species such as buckthorn, multiflora rose, autumn olive and honeysuckle. In some cases, Johnson said, these species constituted 80 to 90 percent of the vegetation in the utility’s rights-of-way.
“To deal with this problem, we shifted from a basal-only herbicide program to a foliar herbicide program,” Johnson said. “This has definitely helped to reduce the proliferation of these multistemmed woody shrubs and vines.”
Darin Sloan, marketing manager for DuPont Land Management in Memphis, Tenn., said strategies and products can be used for invasive species in specific, compared with traditional, species.
“We spend quite a bit of time here designing products specifically for invasives,” Sloan said.
For invasive species, Sloan said, foliar applications can be as effective as basal.
“However, certain products can be more appropriate for foliar applications than basal,” he said. “You have to select the right product for the right use. Basal applications tend to be more labor-intensive, of course, because you have to make sure you have good coverage around the stems. This can be difficult to do in very dense areas.”
For foliar applications on woody and brushy invasives, Sloan recommends a selective herbicide called Streamline.
“We have also recently launched a selective herbicide called Perspective, which can be used in foliar applications for broadleaf invasive weeds,” he said.
Mats Could Solve California’s 10-foot Firebreak Law
As the vegetation control program manager for Pacific Gas & Electric (PG&E), Douglas McPherson is responsible for clearing firebreaks around poles that have the potential to emit sparks or molten material onto the ground. This is the result of California legislation that requires utilities maintain a 10-foot firebreak around their poles during fire season. For PG&E, this involves some 120,000 poles.
“One concern is the potential for erosion after the firebreaks are cleared around the poles,” McPherson said.
The utility began experimenting with WeedEnder mats. These fire-retardant mats that have at least a 15-year lifespan of at least 15 years, deprive root systems of sunlight, yet allow water and nutrients to filter through, keeping root systems alive and preventing erosion.
“We purchased 10 of these mats,” McPherson said. “We put two of them down for training purposes to show people how they staple together. To date, we have only installed one other to actually prevent erosion. As far as we are concerned, it has been working well; however, the customer hasn’t been happy because of the aesthetics of the mat. Right now we are still trying to figure out how we will use them.”
William Atkinson is a freelance writer based in Illinois. Reach him at firstname.lastname@example.org.
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