Idaho Power maintains nearly 5,000 miles (8,047 km) of transmission lines stretching across some of the most rugged and remote landscape throughout Idaho and Oregon, U.S. Moving equipment necessary to maintain the lines by ground is difficult, sometimes requiring permission from landowners and environmental assessments, as well as the addition of new roads. Beyond access issues, it is becoming increasingly difficult to get permission for outages to perform maintenance work. Although Idaho Power has some redundancy, high electrical load in the summer and winter prevents outages during these months; however, outages are possible in the spring and fall.
Idaho Power supplies electricity to more than 500,000 customers that span 24,000 sq miles (62,160 sq km). Since the 1980s, Idaho Power's load has increased by 1,075 MW and continues to grow at about 50 MW per year, with the most rapid growth occurring in Boise and the surrounding area.
Specialized Live-Line Crews
An inspection of Brownlee-Boise Bench transmission lines showed many insulators and dampers needed to be replaced. The project included 103 miles (166 km) of transmission lines between the Brownlee Station in Hell's Canyon and the Boise Bench Substation in the Boise metro area. Idaho Power does not integrate bare-hand hot crews in its internal workforce to perform energized work on its 230-kV lines; therefore, the utility outsourced this project to contractors who provide options for live-line maintenance. Idaho Power selected Haverfield Aviation, an aerial utility contractor, based on its ability to navigate close tolerances and tight electrical clearances as well as its line worker expertise.
Working closely together, Idaho Power's project team and Haverfield's specialized services and safety teams developed a detailed health and safety plan tailored to the utility's project. Contractor personnel went to each structure and took measurements to create a detailed project plan. Each project task was listed, the associated hazards for that task were identified, work procedures were written and appropriate mitigation steps were developed. In addition, specialized tooling needs were identified to reduce hazards. Tailboard discussions were held every morning to review operational tasks, identify potential safety hazards and list mitigation measures to be used for every particular phase of the project.
Following a tailboard meeting, one of Haverfield's 21 McDonnell Douglas MD500 helicopters would long-line the linemen and necessary equipment to the first structure. Typical tools used for the work included attachment hardware and brackets, fiberglass work sticks and ladders, strain poles and ratchet wrenches. Specialized equipment also was lifted into place. Some examples of specialized equipment that could be used on a particular structure follow:
Custom-designed baker boards and support brackets for conductor shoe and insulator replacement
Deadend strain stick assemblies for insulator and deadend shoe replacement
Long custom fiberglass strain sticks for the human external cargo system to position personnel on the structure, conductor or baker boards as needed.
Repairs and Change-Outs
Conductor, damper and hardware repairs at the structure and insulator change-outs were facilitated using a patented support assembly attached to the structure body. These specialty baker boards were extruded fiberglass platforms fitted with specially fabricated brackets and hydraulic jacks that could be attached to a variety of structures.
The boards were lifted by helicopter and fitted into place just under the conductors. A linemen would raise the conductor with a hydraulic lift, disconnect it from the insulators and slide it outward from the structure. Another lineman would then be long-lined onto the platform where he would use an arc wand and bond clamp hooked to his hot suit to energize and connect himself to the power line. Next, the lineman on the fiberglass board would perform work on the conductor while the lineman on the structure would replace the old insulators with new ones using the helicopter.
On angle structures, special adapter brackets and strain sticks were used to hold the conductor and break the load. Two linemen would then be flown to the structure on a mini platform connected to the helicopter with the long-line system. They would be bonded onto the conductor with wands and bond clamps while the helicopter would hover above the conductor. Then the lineman would disconnect the conductor from the insulators and return to the ground. The linemen on the structure would perform insulator change-outs with the assistance of the helicopter and a long line. The process was reversed to reconnect the conductor. Any work needed on the conductor dampers was done at that time with the mini platform.
On double-deadend structures, linemen would be flown to the structure by helicopter and long-lined, and then the equipment would be flown to the structure. Fiberglass ladders would be landed, swung into position and connected to the conductor. Fiberglass strain sticks would be installed into position on the structure by the linemen on the ladder to break the load, to allow the insulators to be changed.
Work on the Brownlee-Boise Bench Project began on Sept. 3, 2012, and was completed on schedule 15 days later. At the conclusion of the project, 42 suspension strings and two deadend strings were replaced, conductor repairs were made as needed and damper installations were done at 66 lattice structures. While the costs are comparable, a ground-based crew would have needed about three-and-a-half months to complete the same work.
Tom Barber ([email protected]) is a project manager at Idaho Power Co. and has 15 years of experience in the electric utility industry. Prior to working at Idaho Power, he spent five years working in consulting at Ralph M. Parsons and POWER Engineers. Barber holds a BSEE degree from the University of Idaho and is a professional engineer registered in Idaho.
Innovations in Aerial Situations
It is becoming increasingly difficult to obtain permission for outages during maintenance on transmission lines. Environmental concerns and a lack of much-needed new power line construction have complicated the situation even more. The burden placed on utilities and their systems by constantly increasing consumer demand and the fact certain areas are fed by radial lines make energized maintenance the only viable solution.
Recognizing a need to address this issue, Haverfield developed a specialty operations division. Composed of a team of experienced pilots, foremen, linemen and groundmen, this division has been tasked with the development of solutions for situations with complex energized maintenance work and construction projects. As many projects present unique problems, the team continues to invent solutions.
A recently completed project presented difficulties that resulted in the design and fabrication of a unique device that will be useful in many future situations. The project required work on structures that were designed for 69-kV lines but installed with 115-kV lines, which made conventional work methods a challenge. The issue was addressed with the development of a hydraulically adjustable, extruded fiberglass baker board with adjustable attachment brackets. This allowed work on the structures to be performed safely, which consisted of switching out pinning plates, insulators and any necessary conductor repairs.
In another instance, a customer requested insulators be replaced on 400-ft (122-m) towers, which spanned over a river crossing. This work needed to be performed energized. The conductors were 3,500 million circular mils and weighed 12,000 lb (5,443 kg) each. In response to the challenge the weight of the conductors created, the team developed a winch capable of lifting 24,000 lb (10,886 kg). The winch was to be mounted above the arm of the structure to help overcome clearance concerns that the situation presented.
In addition, strain sticks and lifting plates large enough to handle the extreme wire weight were fabricated. Because the lines were 345 kV with vertical construction, the team had to attach 80 ft (24 m) of strain sticks together to allow optimal positioning of equipment and linemen to make working on the conductors safe. The final development for the project was a small spacer cart that would work on a single conductor for the change-out of 3,000 lb (1,361 kg) of conductor dampers.
Clearance issues with the middle phase on a 500-kV line for another job required the development of a spacer cart that could be flown and suspended below the helicopter using the human external cargo (HEC) system. The HEC system is used when a lineman is suspended by a long line, 50 ft (15 m) or more in the air from the base of a hovering helicopter. Using the HEC system, the newly designed spacer cart, equipped with a lineman and tools, landed into position successfully on the energized middle phase of the 500-kV line, directly on the conductor.
On another water-crossing job, the customer had 400-ft towers with 5,000-ft (1,524-m) spans. The project required the replacement of conductor weights and spacers. Conventional spacer carts could not travel up the wire without slipping. This required the team to engineer a four-wheel-drive spacer cart that could handle the centenary of the wire without slipping.
Haverfield Aviation | www.haverfield.com
Idaho Power | www.idahopower.com