A solid game plan results in the successful changeout of 345-kV wood structures
Woodpeckers hollowed out baseball-sized cavities in 80- to 90-ft wood poles in Western Massachusetts Electric Co.'s (WMECO) service territory. The utility, which is the operating company for Northeast Utilities (NU; Hartford, Connecticut), discovered the holes while conducting climbing inspections on its transmission-line structures last year.
Woodpecker attacks on utility poles in North America vary from region to region and even by height and type of pole structure. NU engineers had to conduct extensive research to discover what type of woodpecker was inflicting damage on its utility poles.
The utility eventually pinpointed the pileated woodpecker (Dryocopus pileatus) as the culprit. This species, one of the largest woodpeckers in North America, has increased in number since 1920. This type of woodpecker prefers tall open-area transmission poles for building nesting cavities and "brooding" sites, according to the paper "Woodpecker Damage to Utility Poles: Special Reference to the Role of Territory and Resonance" by the late John Dennis, published in Bird-Banding: A Journal of Ornithological Investigation (now the Journal of Ornithological Investigation) in October 1964.
Pileated woodpeckers also burrow out extensive cavities, as deep as 4 ft into the core of the pole, and more alarming, they almost never use the same nest twice, creating new nesting holes each year. Woodpeckers begin roosting in cavities in the late summer or early fall and nesting in holes in the spring.
Due to the type of woodpecker with which NU was dealing, the attacks were almost entirely confined to larger poles, and as a result, the losses were particularly severe. This was because larger transmission poles are more costly, and the attacks took place in remote, relatively inaccessible areas, thus going undetected.
The reason why field crews didn't notice the holes initially is because they were not visible from the ground. Over time, the cavities seriously compromised the bending strength of the poles, making them vulnerable to failure in the event of an ice storm.
NU quickly determined that the damage to some of the poles was so extensive that linemen needed to replace the poles before the winter season. With the exception of the woodpecker-damaged poles, NU's 345-kV circuits were in excellent condition. Therefore, the utility decided to replace the at-risk H-frame structures with like-steel structures to prevent the recurring damage from woodpeckers. The crew identified 16 structures with the highest degree of damage: 14 in the area of Granby, Pelham and Shutesbury, Massachusetts, and two structures in Montague, Massachusetts.
The project was scheduled to begin in early summer 2008. NU elected to replace the H-frame wood poles with like-for-like steel structures from Fort Worth Tower Inc. (FWT; Fort Worth, Texas). The structures were manufactured to be the same height and strength capacity as the existing structures. Once installed, the H-frame steel structures looked similar to the existing structure configuration with the three double-bundle phases aligned in the same position as in the original wood structures.
It was nearly impossible to obtain outage permits during the high-peak summer months on the critical 345-kV line. For that reason, NU opted to do the structure changeout with the circuit energized. WMECO retained Quanta Energized Services' (Kansas City, Missouri) barehand team to help replace the structures.
A Well-Defined Plan
By working together on many projects over the last few years, NU and Quanta had already developed a multi-step work procedure. Each site is unique, requiring flexibility and site-specific planning, but on this summer-long project, the crews abided by the following step-by-step approach to change out transmission-line structures on an energized circuit.
Pre-job briefing. The crew had at least one briefing daily at each new site before work commenced. Each job site had its own job sheet detailing safety risks, site-specific emergency exiting procedures and medical emergency contacts. The crew members also discussed the effects of unique terrain restraints and work procedures for each aspect of the structure build and teardown. Because the work was performed in a high-voltage, energized transmission-line environment, crews exercised an extra level of detail and protocol. The linemen identified and discussed each potential safety hazard daily. If a structure changeout was completed early enough in the day, and time allowed for the work to commence at the next site, the crew conducted another briefing at the new site.
Another part of the pre-job briefing included tools and equipment inspections as well as testing based on barehand safety requirements and company guidelines. The linemen took weight and measurements on each conductor span to ensure that the proper cranes and aerial picks were used at each site. The crew also measured line and (deadend) guy tensions. These tried-and-true pre-job procedures resulted in an excellent safety record. Once everyone was comfortable with the work schedule and all their questions were answered, the construction began at each site with ground preparation.
Ground preparation. Safety was paramount on the job site. At any one time, seven to eight linemen and two to three 100-ft cranes were up in the air while an aerial bucket truck and a digger derrick were on the ground. Terrain and soil conditions varied from standing water, river banks and hilly conditions to other less-than-desirable terrain. These adverse conditions required clearing and in most cases matting, so that crews could perform their work on the ground and in the air from a stable, secure foundation.
Hole digging and pole assembly. Once the crew was able to move equipment and materials to the site, some of the workers used a digger derrick to dig the holes for the new steel poles. The crew dug the new holes and set the structures next to the old wood structures, with the exact same dimension, height, width and pole spacing as the old poles. They encountered soils ranging from soft formations to hard ledge rock. In some cases where the soil was unstable, a casing was spun into the hole simultaneously in the annular space around the auger, to maintain the hole opening.
While the holes were being augured, the rest of the crew laid out the two pole sections. The linemen took a measurement, marked on the side of the pole, and then slip-jointed the two sections together using a 3-ton hydraulic hoist. The workers attached the hoist with bolts to the sides of the two poles and jacked to the manufacturer's predetermined measurement and length. To make sure the friction joint did not come apart, the hoist assemble remained attached to the pole to secure the joint until the pole was upright.
The new steel poles came with preassembled support plates for pole steps permanently attached at intervals on the poles. Once the linemen joined the pole together, they permanently wedged the 100-plus pole steps into the support plates for future climbing and servicing of the structure. Before the poles were erected and the aerial work began, the team used Quanta's proprietary robotic arm called the LineMaster in conjunction with working from buckets.
Offloading the outside phases. The crews relied on at least two LineMaster robotic arms to pick up and spread out the two outside 954 aluminum-conductor steel-reinforced (ACSR) double-bundled conductors. The LineMaster is an insulator assembly mounted on a hydraulically controlled arm at the end of a boom with the capacity to lift 5000 lbs of conductor weight. These picks gave the crew multiple options for addressing live conductor clearance issues. To spread out the two outside phases, the conductor was captured in the fittings, called the “pick,” on top of a crane and “parked” out 3 ft to 5 ft away from the existing structure to allow space to work and maintain safe clearance while standing up the new poles.
Standing of poles and attaching arms. With the conductor parked away from the work area, the linemen stood the new poles erect next to the old poles. The aerial crew then built out the new crossarm structure between the new poles, hanging the new bells (rigid-post stacked insulators) and other hardware on the arms in preparation for attaching the conductors. The only minor change to the original design was the use of solid arms versus lattice crossarms. Originally, the plan was to use the existing lattice crossarms, but as the project developed, FWT and NU agreed that using new steel arms, compared to converting the existing crossarms, would be more efficient.
Hanging double bundles. Once the arm was in place, one or both of the outside phases were taken off the picks and attached to the insulators hanging on the new H-frame structure. The crew then used a single pick to grab the middle bundle and offload it to hang on the new structure. In some cases, this procedure becomes more complicated and involves smaller incremental picking and attaching steps. An example of this situation would be when multiple picks are not set up on the ground due to standing water or an embankment.
Tearing down and loading out. Once the conductors were hung, and the weight and tensioning measurements were taken, the crew removed the old wood-pole structure, loaded up the matting and other tools and equipment, and moved on to the next structure. Each site had a unique set of challenges and environmental issues.
On average, each structure took about three days to complete, not including travel time. In one of the most difficult cases involving a three-way corner structure and standing water, the crew took eight work days to change out the H-frame structure. In another case, a site required a 120-ft pole configuration. The final H-frame structure was placed in early September 2008, and the whole project was on schedule and without incident.
Since the first pileated woodpeckers were discovered, NU has continued to assess the damages, prioritizing each damaged transmission pole according to its risk of failure. A standalone program has been developed to observe, inspect and remediate the woodpecker problem. Each incident is ranked according to severity and recommended remedial action. The pole structures with the highest risk are scheduled for replacement first.
Next year, NU plans to replace an additional 35 structures, again using the multi-step procedure. The goal is to remove the risks of pole failures and to give the woodpeckers fewer places to roost and nest.
Carl Tyburski is a supervisor of transmission lines and field contract services for Western Massachusetts Electric Co., a wholly owned subsidiary of Northeast Utilities. He has worked for NU for 23 years and is now based in Hadley, Massachusetts. His responsibilities include line construction and maintenance in both Connecticut and Massachusetts. NU owns and operates about 3000 circuit miles of transmission lines in Connecticut, Massachusetts and New Hampshire. firstname.lastname@example.org