Over 20 years INMR has visited and reported on hundreds of transmission lines throughout the world – crossing deserts, rain forests, urban areas, towering mountains and other diverse landscapes. While the majority of these have involved fairly conventional lattice type towers, others have stood out due to their high aesthetics, unusual functionality or unique design – in some cases all three combined.
INMR takes readers on a guided tour of what we consider some of the world’s more remarkable transmission structures.
Following destruction by avalanche of towers on two 300 kV circuits in the coastal mountains of British Columbia, Canada during the winter of 1954-55, an engineer named Brian White proposed the concept of catenaries on which phase conductors would be supported. Several years ago, another engineer, Peter Catchpole, utilized the same concept for that double circuit line, one span away and for much the same reason.
There are now two such ‘catenaries’ in a row on that line, both utilizing cables (circa 1160 m long for that from 1955 and about 1220 m for that built in 2008). The catenaries permit a span for the two circuit’s six very large conductors (3,364 kcmils) of circa 2450 m from one pair of standard lattice towers to the next. In other words, over an area of some 1250 x 2500 m across an avalanche prone valley, there are no towers at all. The vertical design load on each suspension insulator string is 75 tons/ phase due to heavy ice accumulation. Access for inspection and maintenance is by helicopter pads mounted on the cables and about 150 m above ground
Tower in Shenzhen Designed for 4 Circuits
Carrying four 220 kV circuits might normally require rather tall towers. However, engineers in China designed a structure that accomplishes this with lower height. The line, which is probably unique in the world, utilizes composite insulators in suspension and glass strings in tension, passes a rapidly developing area near the Baoan Airport, just outside of Shenzhen.
Stately Towers Influenced by Maritime History
A transmission line running through northwestern France evokes the region’s maritime tradition through the use of imposing structures that mimic masts of sailing ships. These tall, elegant towers were reportedly many times more expensive than conventional lattice type alternatives however design, not cost, was apparently the key consideration for RTE, the French grid operator.
Use of such special designs is still relatively new in overhead transmission but is expected only to grow as appearance of lines becomes key to the process of obtaining required public approvals.
Towers Are Eye-Catching Feature Near Highway
Anyone driving from the center of the Chinese city of Jinan to its airport will pass and almost surely notice elegant 220 kV cable transition towers located only meters from the highway. Many such towers see the bulky terminations mounted in an elevated position on the structure, giving it an unwieldy top-heavy appearance. Moreover, the cables, being much thicker than the overhead conductors, add even more unsightly mass from a visual perspective. In this case, designers have dropped the overhead conductor to ground level terminations in an unusual and elegant fashion using a series of angled supports. The overall effect is to turn what might have been a bulky eyesore into what can best be described as a modernistic metallic sculpture.
Futuristic Cable Tower in Korea is One of a Kind
Daejeon, one of the largest cities in South Korea, has been promoting itself as the epicenter of the country’s cutting-edge science sector. With this in mind, engineers at Korea Electric Power Corp. attempted to contribute to this image by designing a one-ofa- kind cable transition tower situated at a busy highway interchange. While relying on conventional insulators, the structure is anything but conventional, leaving the impression of atomic physics.
Tower Developed Based on Capabilities of Composite Insulators & Arresters
The rapid development of hollow core composite insulators as well as polymeric housed surge arresters starting in the early 1990s together provided the impetus behind this innovative 400 kV tower, developed and tested by engineers at Sweden’s STRI. The goal was to utilize the high mechanical strength of the FRP tube in the insulator and the lightweight arrester to ‘de-clutter’ the typical HV line, substituting only four key components for what might otherwise be lengthy insulator strings as well as overhead ground wire. The concept, perhaps inspired by the Trident configuration used on distribution lines in places such as the United Kingdom, excels from the standpoint of efficiency but apparently has so far found only very limited application in Norway due to its comparatively high cost and ‘top heavy’ appearance.