Should a cable drop…
12-01-2022 | Posted by Joaquín Martí
At the risk of stating platitudes, structures meant to last should be designed to do so. But those with a less permanent function also require our attention, as sometimes their failure could entail very serious consequences.
Electric power transmission lines crisscross the country, and so do highways and railway lines. Inevitably, they intersect at many locations and this gives rise to some peculiar problems. It is rare for an operating electric cable to drop, but the probabilities increase when the line is undergoing construction or maintenance operations. And there is no need to describe the potential consequences of a cable dropped across a high-speed railway line or a busy motorway.
To prevent such events, protective structures are erected during construction and maintenance operations of transmission lines that could result in the accidental release of one of the phases. Such structures are not meant to last very long, only while the operations are taking place. But their failure is unacceptable because, instead of protecting against the dropped cable, they would contribute an additional obstacle.
The protective structures need to be fairly robust, as high-voltage lines typically have long spans, the cables are heavy, and their tension provides them with additional potential energy. They must also be capable of resisting the forces being exerted by the wind when the hypothetical cable drop takes place.
Principia has analysed and contributed to the design of several structures of this type, both for highways and for railway lines. It is not a particularly difficult problem, but many alternative hypotheses must be considered and considerable experience is required. In our case the calculations of the interaction of the dropped cables with the protective structures were conducted using explicit integration with the program Abaqus. And physical tests were also carried out to validate some of the analysis results.
On a related subject, we have also analysed the impacts of train locomotives against obstacles encountered on the track, to ensure that the design of their passive safety elements satisfies the provisions of the EN 15227 standard, particularly regarding the collision against a large road vehicle in a level crossing, as well as the collisions against low obstacles.
When travelling by train or car, next time you notice an unusual looking structure straddling your path under an electricity line, you know that pains are being taken to ensure your safety. And that someone contributed a few sums to achieve it.
