An overhead line crossing (see Domain specific aliases) 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.
Domain specific aliases Several related terms are used in engineering, regulatory, and planning contexts. These terms are partly overlapping and may differ slightly in scope or emphasis.
Crossings of roads and railway lines Overhead line crossings of roads, railway lines, and small- and medium-sized watercourses do not normally require special construction. However, in the first years building overhead line when crossing a railway line or a road, a scaffold under the line was required. 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.
Crossings of overhead lines at state borders
There is frequently an anchor pylon on each side of state borders, particularly if the lines on either side 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.
Crossings of other overhead lines 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 the line that is crossed unchanged, 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 on 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. A unique undercrossing of two powerlines can be found north of Kincardine at Scotland at 56°5'17"N 3°43'11"W. Here crosses the powerline Kincardine-Tealing two other lines. One of the two circuits of Kincardine-Tealing powerline crosses these lines on two small pylons and the other circuit via an underground cable.
Special crossings from overhead lines of other overhead lines There are some crossings between two overhead powerlines, which are unique, either as both lines are of special type or the unique way of implementation
Overhead line crossings of aerial tramways Overhead lines should cross the route of an aerial tramway only above it. In principle, over- and undercrossings of aerial tramways are completely regulated. In the case of an undercrossing of an aerial tramway, the maximum safety distances between the overhead line and the floor of the aerial tramway cab must be followed absolutely. Frequently at the range of the crossing section, special precautionary measures are taken. Thus, at overhead line crossings at which the overhead line runs above the rope of the aerial tramway, two catch ropes are occasionally installed to prevent the conductor from falling off the rope of the tramway in case a pylon or insulator were to break. Alternatively, auxiliary cross-bars can be installed on the pylons of the overhead line under the conductors, which prevent the conductor cables from falling in case of an insulator failure on the aerial tramway. Occasionally, the span field of the line over the aerial ropeway can be scaffolded with a rigid construction along its whole length, or at least for the span which crosses the aerial tramway. At crossings at which the aerial tramway runs above the power line, the line is frequently installed on special masts in the crossing range, which scaffold the line in the area of the aerial tramway crossing. Such a measure is not necessary according to power line regulations, but it is often done because, in case of aerial tramway failure, it is possible to rescue people from the tram without switching off the overhead line. Such constructions may be seen at 110 kV power line crossings of the Penkenbahn at Mayrhofen, the Patscherkofelbahn at Innsbruck and south of Zermatt.
Overhead line crossings of broad rivers and straits
Overhead line crossings of broad rivers and of straits, if the terrain on both sides is relatively even, frequently consist of four pylons: two particularly substantial anchor pylons for bracing the conductors of the crossing section, and two tall carrying masts to keep the line high over the water. These pylons have broader cross-bars and greater distances between the cross-bars than the other pylons of the line, in order to prevent the conductor cables from striking against each other during strong winds. In contrast to normal pylons, the two carrying masts at both ends of the crossing are frequently equipped with flight safety lamps, and have stairways for easy access to the top.
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