Transmission lines are generally built with little, if any, concern for aesthetics. Traditionally, the objective of transmission line engineers has been to design the most economic line with acceptable reliability and safety levels. Though these criteria are the most important for line design, a growing concern has been the environmental impact of transmission lines. Utilities must find an acceptable alternative to standard transmission line designs. The general public often considers these lines to be eyesores, thus increasing their opposition to new construction.
One solution would be to make transmission lines invisible. Unfortunately, underground transmission lines cost between seven and 20 times more than overhead lines. An alternative is to make the lines as inobtrusive as possible. To this end, conductors can be made non-specular, or in the extreme, they can be painted green, as has been done with a line in Austria.
If the width of the right-of-way (R/W) is not a problem, the structures can be built very slim using guyed pylons or chainette structures. In congested areas, the R/W can be narrowed by using horizontal-vee or line-post type construction. Still, other utilities use steel poles with davit arms. Yet this is only a partial solution because in the opinion of most people, a steel pole is merely less ugly than a lattice tower. Landscape and Lines
It is relatively easy to permit and build a distribution line. The public understands that a distribution line directly serves their residence and the surrounding neighborhood, but a transmission line is perceived as an unnecessary intrusion within their environment. In general, most of a transmission line route passes through areas where the visual impact is inconsequential. However, permitting the line may depend on a short section that passes through a park, crosses a waterway or road, or intrudes on an area of expensive real estate. In these areas, the public expects designs that do not violate the existing landscape.
The trend towards decreased transmission line acceptance is universal. No longer can engineers rely upon the lowest-cost solution. The real challenge is not to build the lowest cost line (which may encounter a great amount of public opposition) but to design a line that is acceptable to the public at the lowest cost.
An Aesthetic, Yet Practical Solution Imatran Voima Oy (IVO) is the largest utility in Finland. As a parent company, IVO owns and operates more than 20,920 km (13,000 miles) of transmission lines _ approximately 65% of the transmission network in the country _ through its subsidiary company IVS (IVO Transmission Services). Engineering design work is provided through IVO International. IVO International is responsible for the engineering operations of IVO in Finland and abroad.
IVO's structures incorporate artistic design elements to appeal to the general public. Using industrial design principles, main structural elements that can be mass produced are combined with visually appealing features to produce customized, artistic shapes. The designs are intended to avoid the monotonous repetition usually associated with transmission lines.
The design concept became a reality through the multi-disciplinary approach of skilled transmission line designers and a world famous international team of architects and industrial designers. Their work has produced a family of structures that combine reasonable mass production costs with variable, aesthetically pleasing elements.
The design team, led by Professor Antti Nurmesniemi, developed a solution that uses mass produced, galvanized, high strength steel, uniform cross section profiles as the main structural material. Other key features of the design include vertical guys that can double as ladders, customized concrete bases and customized crossarms, which, together with color combinations, create the desired artistic effects. The new concepts have been applied to three projects with favorable results. Consequently, IVO has received numerous inquiries from other countries.
Turku Energy's 110-kV Line Turku Energy, the utility supplying the second largest city in Finland, was planning a 110-kV line to supply power to a new suburb. A 2 km (1.3 mile) section of the line had to cross an environmentally sensitive park area. For this section of line the utility chose to use the IVO-designed tangent structure (Fig. 1). The main structural element is a 29.2 m (95.7 ft) uniform 508 mm (20 inch) O.D. galvanized high strength steel pole, consisting of three sections.
The total steel weight of the structure is 1820 kg (4012 lbs). The crossarms are manufactured of galvanized steel, painted yellow and are designed to resemble the heads of birds. Note the use of the climbing ladder as a vertical bracing element. Two 556 kcmil ACSR 54/7 duck conductors are vertically bundled. The design wind span is 300 m (1000 ft) and the design weight span is 400 m (1312 ft). The design ice load is 2.5 kg/m (1.7 lb/ft). Seven structures were manufactured and installed in this section of line.
The line has received positive reception from the Finnish public. The city of Turku even selected the line section as "Scenic Artwork of the Year." Finland's leading newspaper, Helsingin Sanomat, in an Oct. 26, 1995 feature article enthusiastically described the winning artwork: "Against the autumn foliage, the poles are like trees with yellow birds on their branches, long worms in their mouths."
IVS' Vihtavuori Double Circuit 400-kV Line IVS maintains a 400-kV and 110-kV line that crosses a lake near a major highway. The visual impact of the transmission line had to be considered in this scenic area. In this case, the solution was to use a new double circuit 400-kV structure for a short section of the line. For appearance and to allow for future ugrade, the 110-kV circuit was also insulated at the 400-kV level.
The structure type used was a guyed pylon. Each leg was constructed of two galvanized, high strength rectangular 3.66 by 3.66 m (12 by 12 inch) profiles welded together. The structure was longitudinally guyed with two pairs of guys. The crossarms were upswept for improved aesthetic shape and painted green to blend in with the environment (Fig. 2). The structures were designed for horizontally bundled 1113 kcmil ACSR finch conductors with a weight span of 600 m (1969 ft), a wind span of 500 m (1640 ft) and an ice load of 2.5 kg/m (1.7 lb/ft).
IVS' 400-kV Crossing in Espoo Thirty-two km (20 miles) west of Helsinki, the Finnish National Highway Authority (TVH) is constructing a new multi-level intersection for the beltway around the city. The intersection of the main highways is in a suburban area and extends over 1 km2 (20 acres). Improvements planned for the area include planting thousands of trees and shrubs. Scenic concerns are important to everyone involved in the project.
A conventional lattice structure was not considered acceptable. To maintain the scenic effect of the area, the highway authorities commissioned the design of a new structure for the 400-kV line crossing. TVH agreed to pay the major part of the design and construction cost for a truly unique 400-kV structure. The architectural design of the structure was contracted to Professor Nurmesniemi's studio.
The circuit consists of a 400-kV line with tri-bundled 1113 kcmil ACSR finch conductors. The structure design requirements were a 400 m (1312 ft) wind span, a 500 m (1640 ft) weight span, an ice load of 2.5 kg/m (1.7 lb/ft) and a line angle deflection of 10 degrees. Aesthetic and scenic concerns were more important than a least-cost design because only a single structure was involved. However, the increased structural costs were only a small fraction of the total cost of the highway intersection.
Each of the individual poles of the structure supports a single phase (Fig. 3 & 4). The structure consists of 700 mm (27.6 inch) diameter tubular steel poles rising from 13 m (42.6 ft) pyramidal concrete pedestals. The total height of the structure is 36.7 m (120.3 ft). The crossarms are galvanized and painted, welded steel. Each crossarm is braced with two 50 mm (2 inch) O.D. vertical steel guys. The total amount of concrete is about 120 m3 (4238 ft3) per structure and the steel weight is 13 tons.
Public acceptance of the structures has exceeded even the most optimistic expectations. The structures were named "The Spar-Buoys of Espoo" in an official naming ceremony in November 1995. Government authorities, environmental and scenic organizations, and arts and architectural authorities are all giving the structures high praise. Cost Analysis The new structures can be built with a small cost premium over conventional structures. The relative costs of the three cases described, as compared to conventional lattice or pylon structures, were: Turku Energy 105-110% IVS -Vihtavuori 130-140% IVS - Espoo 200% (in this case the concrete cost was almost 50% of the total cost)
The incremental costs should take into account the increased acceptance and ease of permitting, the willingness of the affected parties to share construction costs, and the unacceptable high cost alternatives for underground or complete relocation of facilities.
Conclusion We learned several valuable lessons after completing the project. Architects and designers can make a major difference in the appearance and acceptance of transmission lines. A good multi-disciplinary design team can achieve these results for a minimal cost increase. Compared to placing a line underground or dealing with major routing changes, improving structure appearance is an attractive low-cost option. The amount of line affected by aethestic considerations is relatively small. Concentrating on the improvement of these key line sections makes the overall permitting process easier. Finally, the public relations benefits should not be forgotten. An aesthetically designed line is perceived as an added attraction to the landscape instead of an unwelcome intruder. The new IVO-designed structures received the Finnish Award for Innovative Steel Structures in 1995.
Future Designs In addition to the completed projects, IVO has several new designs in varying stages of completion. A double circuit modification of the Turku Energy structure will be used in a twin 100-kV line in southern Finland. Also nearing completion are 100-kV substation supporting structures. Operating trials are underway using 110-kV covered conductors to allow a reduced phase spacing of 180 cm (5.9 ft). The towers for these lines will consist of another family of narrow, inverted U-shaped structures. TDW
Kai Nieminen is a design manager at IVO International Ltd. in Finland. He has personally designed hundreds of tower types for 110-kV and 400-kV lines in Finland and other countries over the last 20 years. He has participated in numerous projects and advisory tasks for electric utilities and industrial enterprises regarding design, rehabilitation, supervision and commissioning of transmission lines. Tapani Seppa is president of The Valley Group, Inc., Ridgefield, Connecticutt, U.S., a company specializing in leading edge technologies for the transmission and distribution industry. He has held a number of executive and managerial positions in several companies serving the utility industry. He received his MSEE degree from Helsinki Technical Institute, Finland. He serves on many of the committees and task force groups within IEEE and CIGRE and has published numerous technical articles. He holds several patents.