Not Just Nature to Blame For Power Outages
Lehigh Valley – PPL points to three outdated practices causing problems in a high-tech world
Mother Nature may have been the primary cause of the widespread power outages last weekend that left about 400,000 customers of PPL Electric Utilities in the cold and dark.
But interviews with PPL officials and public utility experts suggest some very human decisions also played a key role in the third-worst power outage in the company’s history:
- PPL has been using decades-old easements that are too narrow to protect major power lines. The storm felled 10 69-kilovolt transmission lines, darkening thousands of homes.
- A tree-trimming plan adopted in the 1990s that is better for trees and popular with customers also leaves distribution lines vulnerable to falling limbs and sagging branches.
- Like most other domestic utility companies, PPL has chosen to keep utility lines above ground, saying it would cost ratepayers too much to bury the lines, where they would not be threatened by wind and snow. In Europe, however, utilities in a number of countries have worked cooperatively to put lines underground, following street and highway rights of way.
Some of the choices that have come to shape the Lehigh Valley’s power grid were made a long time ago, others more recently. But all involved value judgments and balancing acts that reflect the priorities not only of PPL, but also of the communities and various other constituents served by the utility.
A comparison of PPL’s performance to that of other utilities is nearly impossible to make under the record-keeping requirements of the Pennsylvania Public Utility Commission. The PUC allows utilities to exclude storm-related outages from biennial evaluations of maintenance and repair plans, arguing that storms like last weekend’s are statistical anomalies that distort regular assessments, never mind the increased frequency of extreme weather.
Indeed, hurricanes, tropical depressions, snowstorms, ice storms and windstorms over the past decade account for nine of the 10 worst outages in PPL’s century-long history. Three of those — Hurricane Irene in August, a Memorial Day weekend windstorm plus the recent pre-Halloween nor’easter — occurred this year.
In the report from its most recent biennial inspection, which covered 2006-08, PPL said the reliability of its electric supply “was severely distorted by unprecedented storm experience.” It’s a sentiment almost certain to be expressed in the company’s assessment of the current period, as well.
The easement for the 69 kv transmission line feeding parts of south Bethlehem, including Lehigh University, cuts a clean swath through the trees of South Mountain. On either side of the 70-foot-wide path, the forest rises like a giant hedge.
Clearly, the problem during the Oct. 29 storm was not a lack of attention by PPL’s tree-trimming crews. The company recently increased the frequency of vegetation management on 69 kv lines from about a five-year cycle to about a three-year cycle. It also inspects the lines by helicopter on an annual basis.
The problem was the easement itself — specifically, its width. The 35-foot clearing on either side of the easement’s center line provided insufficient protection from the 100-foot trees looming nearby.
A dozen of those trees — their root structures weakened by excessive rain and their tops weighted down by snow-covered foliage — gave way and dragged the 69 kv line to the ground. The line was strung on a variety of steel and wooden poles anywhere from 65 to 90 feet tall. At the low point of its arch, the line was roughly 40 feet from the ground.
Most of the trees that hit the line fell from the steep slope above the easement. But at least one — as if to remove any doubt about the role of easement width — came from the downward slope.
“Look at how tight that is,” Phil Walnock, PPL’s head of vegetation management, said of the easement last week as workers repaired the line. At work was a small army of bulldozers, bucket trucks and other heavy equipment.
The easements, or rights of way, around PPL’s transmission lines are legal agreements negotiated with individual landowners. And many of the easements PPL relies on today were established as far back as the 1920s by the small, local utilities that would later be brought into PPL.
Today, when PPL wants to create an easement for a 69 kv line, it seeks a 100-foot berth. But some of the old easements are as narrow as 50 feet.
“When we absorbed those easements, we had to take them as they were,” said PPL spokesman Paul Wirth.
One explanation for the continued existence of such narrow corridors is that transmission lines under 100 kv are not regulated by the Federal Energy Regulatory Commission. After a massive blackout struck much of the Northeast in August 2003, FERC mandated stepped-up vegetation management for higher-voltage transmission lines, including the 230 and 500 kv lines that constitute the backbone of PPL’s transmission grid.
None of those higher-voltage, FERC-regulated transmission lines failed last weekend. Meanwhile, parts of south Bethlehem served by a fallen 69 kv line stayed dark for five days.
On shady city avenues and in wooded rural settings, trees lend an air of seclusion to homes and keep the elements at bay by diffusing summer sun and deflecting winter winds. But those trees often share space with the power lines that deliver electricity to homes, and electric companies are locked in a never-ending process of keeping limbs and distribution lines apart to ensure safety and reliability.
The tree-trimming practices used by most, if not all, electric utilities are outlined in a set of standards developed by professional arborists and published by the American National Standards Institute. The standards, first issued in 1995 and most recently revised in 2008, provide a framework of best practices for utilities to develop their own strategies to keep trees tamed.
Arborists say the only foolproof way to ensure trees never damage power lines is to remove them, but that extreme measure is impractical in terms of cost and aesthetic impact.
“Property owners aren’t going to allow the utilities to come in and remove the trees in their backyards, but that creates a certain amount of risk,” said Philip Charlton, director of the Utility Arborist Association.
Utilities manage that risk by trimming trees on a regular basis to maintain a safety zone between limbs and wires. The process has evolved in the last 20 years to include practices that result in better-looking and healthier trees and reduce the chance that limbs can fall on power lines, Charlton and others say.
“[The utilities] were notorious for the practice of topping, which is rounding the tree off to the height below the wires they thought they could get away with,” said Reds Bailey, an arborist and chairman of the Emmaus Shade Tree Commission.
They also used a method called “flat-siding,” in which tree trimmers cut all of the branches on one side of a tree to maintain line clearance. But those methods left trees looking ugly and weren’t particularly effective, said Henry Gerhold, a retired Penn State University forestry professor.
Gerhold said topping and flat-siding leave trees prone to disease through fungal and bacterial infections and leave the interior of the tree exposed to the weather. And when the limbs grow back, they’re weaker because the tree’s branching structure has been disrupted.
That process was replaced by directional pruning, a technique developed by foresters and arborists.
Gerhold said directional pruning involves removing entire limbs on the side of a tree closest to a power line, rather than leaving stumps. Although in some cases the practice leaves trees with an unusual “V” shape, it encourages them to grow away from power lines and allows them to retain a more natural structure.
PPL spokesman Michael Wood said the company adopted the tree care industry standards when they were published in the 1990s, and since then the utility’s vegetation management program has been recognized by the National Arbor Day Foundation. PPL budgeted $33 million on vegetation management in 2011, up from $25 million less than five years ago, Wood said.
Telephone poles or trenches
Utilities say they commonly hear from customers after hurricanes or damaging winter storms: Why don’t you put utility lines underground?
“It would be too destructive and too expensive,” said Sibel Pamukcu, professor of civil and environmental engineering at Lehigh University.
To move lines underground, service would be interrupted, streets and sidewalks would be dug up and residents would face hazards from long-running construction, she said.
Burying high-power transmission lines that run along large rights-of-way also is costly because those lines run through populated areas and cross roads, she said.
Once they’re in the ground, utility lines are not maintenance-free. Underground water can be a costly problem, she said. “We live in a sinkhole region,” Pamukcu added. “Underground construction is not always a said-and-done thing.”
By the Morning Call, distributed by MCT