Overhead line crossing

An overhead line crossing is the crossing of an obstacle—such as a traffic route, a river, a valley or a strait—by an overhead power line. The style of crossing depends on the local conditions and regulations at the time the power line is constructed. Overhead line crossings can sometimes require extensive construction and can also have operational issues. In such cases, those in charge of construction should consider whether a crossing of the obstacle would be better accomplished by an underground or submarine cable.

Overhead line crossings of roads, railway lines, and small- and medium-sized watercourses do not normally require special construction. However, in the first years of overhead line building a scaffold under the line was required, when a railway line or a road was crossed. Later in Germany and some other countries on each end of a powerline crossing of a state-operated railway a dead-end tower was required, which can still be seen on some old power lines. For overhead line crossings of motorways the pylons must be rebuilt before they wear out, because these demand additional maintenance. If local conditions are appropriate, an overhead line can be implemented by way of a valley bridge. For example, the Koersch valley bridge near Esslingen, Germany carries the 110 kV, three-phase line of the EnBW AG with 2 circuits. Because of the danger of short circuits from falling objects, undercrossings are typically avoided.

There is frequently an anchor pylon on each side of the border, particularly if the lines on either side of the border are operated by different companies. This setup reduces maintenance work, which would otherwise require direct coordination of workers on both sides of the border, and avoids possible authority problems associated with border crossings as much as possible.

At crossings of overhead lines by other overhead lines, the two lines must be kept at the necessary safety distances between the lines and the ground. As a rule, the line with the lower voltage passes under the line with higher voltage. Construction workers try to plan these crossings in such a way that their construction is as economical as possible. This is usually done by leaving unchanged the line that is crossed, if possible. Undercrossings of existing lines are often constructed in proximity to the line's pylons, since this can often be accomplished without raising the existing pylons and while keeping the necessary safety distances between the ground and the other line.

In the course of undercrossings the pylon picture is frequently changed, and because of its small height it is preferable to create an arrangement with conductors in one level. Sometimes at such crossings there can be problems because of the maximum pylon height allowed for flight safety reasons. If it is not possible at a given location for the pylons of the upper line to be built at a necessary height, the line running below it will be rebuilt on smaller pylons or replaced with an underground cable.

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Wikipedia