by Brian Parker
Environmental concerns and lack of new power line construction because of imposed restrictions are making it increasingly difficult for utilities to use planned outages during transmission line construction and maintenance.
Burdening power companies and their systems is a constantly increasing consumer demand, plus certain areas are fed by radial lines. These factors make energized maintenance the only viable solution. Yet, working on energized systems involves risks that require highly specialized tools and techniques.
|Linemen are positioned at the structure with the mini platform to replace conductor dampers. The platform was developed to allow quicker, safer access to the conductor near the structure when working with a single conductor.|
Usually considered a modern procedure, live line work has been used since the early 1900s, the beginning of the high-voltage transmission industry. Equipment and work methods evolved to meet the demands. By the 1960s, new methods enabled field-workers to come into direct contact with the highest-voltage lines.
Three methods of performing live line services mitigate the considerable hazards of working on energized power lines. They are all intended to prevent current flow from equipment and through linemen.
Hot sticks, insulated poles used when servicing energized lines, allow linemen to work safely while maintaining minimum clearance distances from live equipment.
They were developed and first used in the 1920s. The poles, then made from baked wood, were used for jobs such as replacing insulators and fuses.
As the operating voltages increased, techniques evolved to protect workers. A major advancement came with the development of fiberglass in the late 1950s. Fiberglass provides excellent insulation, and unlike wooden poles, fiberglass hot sticks are weatherproof. Fiberglass allows hot stick working at the highest operating voltage.
In addition, tools such as hooks and socket wrenches can be mounted at the ends of fiberglass hot sticks. Advanced hot sticks even can use pneumatic and hydraulic power tools.
|A fiberglass ladder is flown into position. A lineman was lifted off the structure and landed on a fiberglass ladder, where he energized himself. The lineman on the ladder then attached strain sticks to the conductor. The linemen on the arm tightened the strain sticks to break load on the insulators, allowing the lineman on the ladder to disconnect the conductor in preparation for insulator removal.|
Insulating Rubber Gloves
A lineman protected by insulating gloves, along with other insulating equipment, can work in direct contact with live lines.
Gloves protect a worker at the first point of contact with energized lines. This is the point where current would enter the body in case of contact. Insulating material such as blankets and line hose protect the worker from exposure at the second point of contact where current would leave the body.
The first procedures for barehand working were developed in 1960 by a high-voltage engineer. Techniques were refined in the laboratory and during fieldwork.
During barehanded, energized work, a lineman is in direct contact with an energized line. Prior to contact with the live lines, the worker's body is raised to the same voltage as the live parts. Because the lineman and live lines are at the same voltage, no current flows through the worker.
Upon completion of the tasks, the process is reversed to allow the worker to safely disengage from the power line. Barehand work allows for greater dexterity than the hot stick method and can provide the preferred option under certain conditions. With this technique, lines can be spliced or insulator strings, conductor spacers and vibration dampers can be replaced without loss of supply.
|A crew changes insulators on a double deadend structure. Because of live-line clearance issues on this type of structure, a special hydraulic, nonconductive baker board was developed to allow safe and fast access to the insulator strings and conductors. Also, gin poles with nonconductive rope and motorized winches were developed to safely remove and install the insulator strings on the structure. The helicopter removed the insulators from the gin pole once they were safely raised into the clear. It then returned with new insulators that were transferred to the gin pole and lowered back into position.|
Aerial line services used in new construction, repair and maintenance have proven to boost productivity and efficiency. Where ground-based methods require large teams of professionals and significant heavy equipment to complete similar tasks during a longer time, aerial services can become the force multiplier and allow for more work to be completed within the same time, delivering quality services safely and on time.
What previously was used as an emergency response to line outages (in the form of aerial patrol) has emerged into a multifaceted source of solutions for transmission construction support and repair, replacement and maintenance needs. During the past 30 years, the field of aerial power line services has developed into an expanding field of helicopter applications. Aerial crews use specialized tools and equipment to provide a safe, fast and efficient alternative to ground-based services with measureable operational cost savings. For example, research by Dominion Power gleaned from a recent project involving 260 structures shows that using aerial services provided up to a 67 percent cost savings, and time was reduced by up to 99 percent when aerial services were used for inspection and maintenance, according to a Dominion representative quoted in Prince William Today.
A lineman wearing a Faraday suit, a pair of overalls made from conducting fibers, can work on live, high-power lines when transported via helicopter. Conducting gloves and socks also are necessary and leave only the face uncovered.
A worker can work off of a platform fixed to the helicopter or be lowered from a long line. As the lineman approaches the wire, an arc will form as the worker is charged. The worker must immediately bond to the line to prevent further arcing. He or she may use a conducting wand during the approach to make the connection. Once on the wire, the worker and the line are at the same voltage, which provides safety from shock because no current passes through the worker's body.
About the Author: Brian Parker is executive vice president of Haverfield Aviation and has direct oversight of all of Haverfield's operational activities. The company has developed a Specialty Operations Division operated by a team of experienced pilots, foremen, linemen and groundmen who develop solutions for customers with more complex energized maintenance work and construction projects. Parker received flight training in the U.S. Army and was selected to become an elite Aero-Scout Pilot.