Overhead line crossing

An overhead line crossing is the crossing of an obstacle ( Road, river, valley or strait ) through a transmission line.

The execution of an overhead line crossing is strongly dependent on the local conditions and to the point of construction prevailing rules for line, and at intersecting roads from the rules. Thus, for example, at crossroads of shipping routes headroom priority. However, overhead line crossings are performed similarly in many similar cases.

Overhead line crossings can do in some cases elaborate constructions required and also bring operational disadvantages. In such cases, consideration should be given to whether an execution of the intersection of the obstacle is more economical than underground cable or submarine cables. Also tunnel ( and culverts ) provide an opportunity to the underpass of rivers with cables. Bridges can both overhead line masts carry (like the Storstrømsbroen or the Cologne South Bridge ) as also have cable channels.

• 7.1 Examples

Overhead line crossings of roads and railway lines

Overhead line crossings of roads, railway lines, small and medium-sized watercourses require no special buildings generally. However, in the early years of the overhead line construction was ( 1910 / 1920 ), it requirement that at intersection of roads a protective bridge had to be built under the direction. Later had for crossing an overhead line with a government railway line on both sides of the railway line a Abspannmast be built, which can be seen especially in some older overhead lines, like those of the north-south line, very nice. Sometimes the pylons need to be replaced prematurely for overhead line crossings of highways and expressways, as there are for this increased static requirements.

If, due to the local conditions appear appropriate, an overhead line can also be crossed by a viaduct. For example, crosses the Körschtalviadukt a double-circuit 110- kV three-phase line of the EnBW AG. For obvious reasons, such as the risk of short circuits caused by falling objects, one tries to avoid such undercrossings. Examples are the Brenz Viaduct, Körschtalviadukt and the Main Bridge Gemünden.

Overhead line crossings of state borders

Are national borders, especially if the line segments are operated on both sides of the border by various power companies, often crossed with a tension field that consists of one Abspannmast on both sides of the border. It thereby reduces maintenance work that would require a direct coordination of workers on both sides of the border, to an absolute minimum and avoids any problems of competence for cross- cross- section of line as much as possible.

Intersections of other overhead lines

In the mutual crossing of overhead power lines the necessary mutual security clearances and security clearances must be kept to the ground. As a rule, this line is generally below the results with the low voltage to the higher voltage. Basically one tries to plan such intersections so that they will be realized with minimum financial outlay. This is usually achieved, in which one can be as stable as possible to the intersecting line. However, it lowers if that line is to be crossed by the newly constructed line, often at the intersection of any existing ground wire to the height of the top cross-member from to reduce the overall height of the masts of the line to be crossed. Under Cross the new-build line an existing line, an attempt is often to realize this in the near masts of this line, as often the necessary safety measures are ensured respect to the ground and the other lines in this case, without increasing the overall existing pylons. In the course of undercrossings the mast image is frequently changed and due to the low height of under crossing the line a level arrangement of conductor cables preferred. In line crossings, there may be problems due to the given reasons of flight safety maximum mast height under certain circumstances.

A further possibility is the creation of a pole which receives the current circuits of the two intersecting lines. It can also be used, if necessary, for realizing a connection between the two lines.

If it appears that no opportunity at one of the locations of the poles of the traversing line to achieve the required height, it will be wired or driven in the area of the crossing portion of the line on the lower mast heights. An unusual version of the mutual crossing of overhead power lines exist north of Kincardine in Scotland. Here, the high-voltage line Kincardine Tealing passes under two other high-voltage lines. One of the circuits of the line Kincardine Tealing crosses under these lines as an overhead line on the lower masts, the other as underground cable.

Overhead line crossings of cable cars

Overhead lines should, if at all, crossing the line a cable car just above this.

The required separation distances of overhead power lines to the ropes of a cable car, refer to the relevant regulations on the construction of cable cars and overhead lines. In the case of an under-crossing cableway the necessary security clearances must be ensured between the overhead line and the bottom of the cable car even in the worst case. Basically, both over-and under crossings by the relevant provisions fully resolved.

However, to take special precautions in the area of the crossing portion often. In overhead line crossings in which the overhead line runs above the ropes of the cable car, two safety ropes are occasionally attached, intended to prevent in the case of breakage of the overhead line mast or mounting insulator that the conductor rope falls on the cable car. Alternatively, auxiliary members may also be mounted on the pylons under the conductor cables, which prevent a crash of the conductors on the cable car line. Occasionally, the span of the cable with the cable car with a rigid structure will be upgraded to full-length or at least in the area of the cable car. This version can be found for example in the cable car from Caracas.

At intersections where the overhead line runs below the supporting cables of the cable car, the line is often laid at the junction of dedicated masts on which scaffolded the line in the cable car crossing. Such a measure is not absolutely required by the relevant provisions of the overhead line construction, but it allows in the case of an accident, the rescue of persons from the cable car without the overhead line must be switched off. Such constructions can be found at 110 - kV transmission line crosses the Penkenbahn in Mayrhofen, Patscherkofelbahn in Innsbruck and south of Zermatt.

Temporary shelters

If the transmission line is under construction crosses a railway line, a cable car, a road or other transmission line, it must be ensured that down hanging ropes not obstruct traffic; that they do not come with standing under power lines already in contact, which would result in a short circuit. Therefore, a wooden frame is built respectively on the lower obstacle.

Overhead line crossings wide rivers and straits

Overhead line crossings wide rivers and straits exist if the terrain on both banks is relatively flat, often from four poles: two tension towers particularly massive type for bracing the junction portion and two support poles high altitude to ensure the necessary line height above the waters. These masts are equipped with wider beams and larger Travers intervals than the other poles of the line to prevent clashing of the conductors in strong winds. In contrast to normal Freileitungsmasten the two support poles are often characterized on both side of the intersection as a flight safety barrier and mountable on stairs.

Overhead line crossings of rivers and straits with widths of over two kilometers, are often inefficient, and very unfavorable under operational conditions, since because of the risk of wind -induced vibration movements of the conductors very large conductor spacing must be chosen or insulating spacers must be fitted between the phases in the span. Since the consistently used in high voltage lines bundle conductors in much greater extent tend to cable vibrations as single ladder, they can not be used, whereby the crossing section under circumstances where the maximum capacity of the cable can be determined section in many cases. Another problem follows from the fact that you can not build the masts at the two ends of the cross section of arbitrarily high economic and licensing reasons, on the other hand often times must observe a considerable minimum height of the line because of the waterway, which is why a high tensile stress in the conductor cable occurs with large spans. This tension only grew ropes with high steel shares, but at the same weight a poorer electrical conductivity than the usual conductor cables have copper, Aldrey or aluminiumummanteltem steel, which also leads to an impairment of the electrical load. For this reason you should always check with waters from about two kilometers wide, whether execution of the crossing line as laid in the water Cables ( submarine cable ), with a width of about five kilometers, is the only viable solution for bodies of water can be carried out. If the area to cruising waterway is not too deep, one or more overhead line masts on caissons can be built in the waterway. A running example is the overhead line crossing of Lake Maracaibo. The approval of such designs is very problematic in navigable waters, as established in the water overhead line masts represent dangerous obstacles for the shipping industry in particular in the fog. Optionally small poles or cross members can be installed on the bridge body to receive conductor cables also to a bridge, which crosses said waters. Such a solution, which is expected to bring in particular at the bridge maintenance safety problems was realized in the Storstrømsbroen in Denmark. It can happen quite the way that overhead line crossings broad waters are replaced by cable laid in water. Thus, the overhead line crossing the Strait of Messina, which belonged with a span of 3,646 meters, the longest overhead line crossings and their intersection masts with a height of 200 meters to the highest pylons in the world was, because of their low electrical load replaced by a submarine cable.

Examples

• High-voltage line to the island of Zhoushan
• Yangtze overhead line crossing
• Yangtze overhead line crossing Nanking
• Yangtze overhead line crossing Wuhu
• Pearl River transmission line crossing
• Orinoco overhead line crossing
• Elbe & Köhlbrand, at the time the three highest overhead line crossings in Europe Elbekreuzung 1
• Elbekreuzung 2
• Köhlbrand overhead line crossing

Overhead line crossing of valleys

Overhead line crossings of valleys consist of two tension towers on both sides of the valley. If the topography of the valley is suitable, this need not be very high. For very wide valleys, it is advantageous to provide for each phase of its own mast to achieve a sufficient distance from the conductors from each other. In these cases, is located behind this is often not a further tension tower to perform the angle change of the conductor cables. The last section mentioned problems related to large spans exist, of course, in these cases, but, if no high crossing masts are needed by a suitable topography, very economical an almost arbitrarily large distance between the conductors can be achieved by using a separate mast for each phase.

Examples

• Overhead line crossing the Sognefjord
• Overhead line crossing the fjord of Ameralik to Greenland, the longest span over 5 km.
• Surge of Eyachtals (Appendix 615)
• Surge of Enztals in Bad Wildbad
• Surge of Nagoldtal in bathroom love cell
• Surge of Weisstannentals.
• Rhine overhead line crossing Hirzenach - Oberkestert

• Overhead line crossing