What is really expected from a power line structure? Is it only a technical necessity, an object of design excellence or a piece of land art? The best answer probably lies somewhere in the middle of all three.
Structure design can make a power line interact much differently with its surroundings.
Because there are so many power line structures and because they are often situated along busy roads and highways, appearance has become almost as important as function. Towers perceived as damaging the natural landscape quickly become objects of public disapproval. In fact, that is precisely why the power supply industry is in a situation where it must overcome great obstacles to erect yet more of them.
Decommissioned 400 kV lattice towers now used as land art along highway in Denmark.
One of the challenges facing all line planners is optimizing design to meet mechanical and electrical performance as well as cost and durability requirements. Clearly, a technically demanding item such as a power line structure needs to be far more than something that is only pleasing to look at. Moreover, since these technical challenges vary with voltage, a new design approach may be needed whenever voltage levels change. A structure designed and optimized for 220 kV may not work effectively for other voltages.
Should a power line structure only be beautiful to look at?Focus on design excellence versus technical excellence can lead to radically different visual impact.
It is also important to take conductors into account since these have significant visual presence as a transmission line moves across the landscape. That makes configuration of conductors as important to consider during line design as are their support structures.
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Yet another important aspect of design is choice of materials. There are now far more options available than when lattice towers were first designed a century ago and a range of alternative materials is available to help overcome the generally negative public perception to lattice structures. Using the latest generation of materials can even help optimize speed of construction and lower project cost – apart from the goal of contributing to improved appearance. Similarly, uniformity of materials used in structures can help improve visual impact by reducing unnecessary clutter.
Concrete and wood laminates used for both mast and cross-arm in these structures in Switzerland (left) and the U.S. (right) help minimize visual impact.
One group of materials being closely examined these days are fibre composites whose intrinsic insulating properties open entirely new possibilities for power line structures. For example, such a structure can be designed without requiring traditional cross-arms equipped with insulator strings since the structure itself effectively acts as insulator. This allows structures that further minimize visual impact. Proper use of fibre composites can also help compress structures and minimize a line’s height, subject to meeting ground clearance and electric field requirements. Similarly, utilizing the insulators themselves as cross-arms can reduce tower height as well as number of different structural members.
These 400 kV structures in Belgium utilize insulator cross-arms to maintain same height as 150 kV structures they replaced.
It is clear that there are not only challenges but also opportunities when it comes to expanding the power grid while minimizing resistance from affected communities. But to realize these opportunities, line designers will have to go beyond their ‘comfort zone’ of relying only on tower concepts of the past. A contemporary power structure with high design component is the best way to overcome opposition to new lines and, through its appearance, remind the public that electricity is the only sustainable solution to our long-term energy needs.
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Given the above considerations, some of which were part of a past INMR article contributed by industrial designers, Bystrup, in Denmark, below, in random order, is a selection of admirable power structures seen over nearly 30 years reporting on overhead lines across the globe. These are referred to as ‘admirable’ because they have succeeded not only to fulfil their basic function of transporting electrical power but also do so with high aesthetic value and/or minimal adverse visual impact on their surroundings. Some are even inspiring to look at and project a positive image for the power supply company that operates them. In a world populated by mostly monotonous and occasionally bizarre power line structures, this is worth admiring.
These otherwise mundane lattice structures in Norway have put on a coat of camouflage to blend into their much visited forest surroundings. The conductors will be glare free and glass insulator strings will be coated in green RTV silicone material to eliminate reflection. The goal here was to stand out by not standing out.The 220 kV Mudarra-La Olma line north of Madrid, Spain was Red Eléctrica de España’s first line designed primarily with composite insulators and follows a corridor once occupied by a 132 kV line. This simple structure design offers comparatively little visual impact even viewed against a backdrop of flat agricultural land.This 735 kV portal tower design was built in the aftermath of the 1998 ice storm affecting the region around Montreal. While Hydro Québec’s normal specifications for conventional 735 kV lattice suspension towers are that they must withstand 45 mm of ice, structural reinforcements as well as reduced spans increased this design criterion to 55 mm. Apart from meeting the need to be as visually unobtrusive as possible due to a busy highway alongside their route, another consideration was local farmers who did not want a large tower footprint.This stylized design runs near Los Angeles and stands out in a power corridor populated by the usual uninspired lattice towers one sees almost everywhere. What makes this structure worth admiring is its high artistic value and whimsical appearance.This tower design near Oslo, Norway is admittedly top heavy due to its use of a trident of hollow core insulators along with a line arrester to eliminate need for a shield wire. Yet it succeeds brilliantly in transporting a 400 kV line through the heart of a neighbourhood of country homes with the least amount of visual clutter.This compact tower runs near Haifa in Israel. Unique cross-arm design manages to turn an otherwise non-descript structure into something worth noticing, especially since it seems to be looking back at you.The Matagorda Tower in southern Spain dates back to the 1950s and demonstrates that gargantuan dimension need not doom a power structure to being an eyesore. Majestic yet graceful and with well-proportioned lines, it rises to 158 m to transport two 132 kV lines across the straits of Cadiz. As much a local icon as the Eiffel Tower.This design of 500 kV line running to Beijing, China is not only easy on the eye but succeeds in keeping all conductors within a narrow window, minimizing the amount of sky they consume.Making a cable transition structure blend into its surroundings can be a huge undertaking, given all the different equipment and protrusions that are bound to add clutter. Yet this Swiss power utility has succeeded in using polymeric arresters in a vertical orientation to reduce net visual impact. The neutral colors and arrangement of terminations, angled harmoniously with conductors, even add an unexpected element of style.The bold design of these elegant 400 kV structures in the Netherlands seems to reach to the sky yet still does not conflict greatly with the pastoral surroundings while also achieving reduced line corridor width and lower electromagnetic field.The 230/69 kV Schrader Line near Phoenix, Arizona is over 20 years old yet remains a masterpiece of minimalism. Its verticality ensures comparatively little clutter of the sky.
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This stately though apparently very costly structure north of Paris was inspired by the masts of ships and reportedly helped convince local authorities to support a new line running through their community.This 400 kV structure in Switzerland was part of the world’s first compact line at such voltage and relies on a bi-dimensional articulated design supported at the top by the ground wire as well as the conductors attached to it through pivoting cross-arms. The structures, although 56 m high, offer comparatively low visual impact with height dictated by the need to maintain the same electromagnetic field as the 125 kV line being replaced.This line passes the environmentally sensitive Everglades of south Florida and succeeds in looking like any rural wood frame line, yet transports 500 kV over orange groves.The ±400 kV line running over 1000 km from Geermu in Central China to Tibet is admired mostly for its engineering and for the determination of the workers who put it up in permafrost and at 4500 m. Its perfect combination of proportion and symmetry give it a sturdy yet elegant look.Sometimes the best structure is none at all. Here at a lovely viewpoint to Cape Town, South Africa, catenaries were used to take advantage of rocky protrusions on either side of the power line corridor. When driving up to visit, INMR’s host pointed excitedly toward the rising mountain ahead and exclaimed: “Do you see it? The invisible tower?”The 400 kV Eagle Pylon running through Jutland, Denmark illustrates that transmission towers can also be unique and uplifting. Unfortunately, the original design with all conductors carried on a single sweeping cross-arm and with rusted mast was nixed by local farmers. Compromise often results in second best.This elegant beauty, designed for the last section of a line supplying the 1992 World’s Fair in Seville, Spain, ticks every box for aesthetics and high design value. It uplifts the spirit and forcefully demonstrates that power lines can contribute to and not detract from their surroundings.
