Salzburg line

Land is generally appropriated either when a pylon is to be erected on it or if it is to be traversed by a transmission line, in which case an easement must be granted. The compensation paid for appropriated land is regulated uniformly for all property owners by a framework agreement entered into with the Chamber of Commerce of the State of Salzburg in October 2010.

If the land appropriated is forested area that has to be cleared in order to install the lines, the compensation to be paid is assessed by an expert on the basis of the framework agreement. The assessment is made in accordance with recognised methods for appraising the value of forested areas and takes the following into account, among other things:

• permanent loss of use;
• loss of future revenue due to felling immature forests;
• compulsory use at economically inopportune times;
• forest management hindrances;
• decrease in land value and yields; and
• damage at forest edges.

Sometimes it’s necessary to fell trees located on the land appropriated for a project, at least during the construction period. After inspecting the existing stock of trees in accordance with the relevant specifications, the surface area in which trees are to be felled is calculated such that no trees can fall onto the line.

Three main factors are significant here:

• the tree height;
• the height of the lines; and
• the slope of the land.

In many cases, the lines cross the forest at such a height that it is not necessary to fell any trees for construction or operation of the line. APG pays compensation pursuant to the framework agreement in such cases.

Once the construction work is completed, the area along the transmission line route is reforested in accordance with the conditions stated in the EIA approval notice. The property owners are able to choose whether they want to reforest their land themselves in return for the compensation stipulated in the framework agreement, or if the reforestation should be undertaken by a firm contracted by APG that will also take care of plant cultivation until care is no longer required. In any case, the building authority responsible for forest ecology checks to ensure that the conditions listed in the approval notice have been complied with. 

The 380-kV Salzburg line is being built as an overhead line, since this form of technical implementation corresponds to the current international state of the art as well as operational practice. Given that the Salzburg line is of trans-regional significance, it must meet N-1 redundancy criteria. N-1 redundancy refers to an international safety standard that must be adhered to in planning and operating power lines and transmission grids. This is a necessary precaution to ensure that the supply of electricity is not disrupted in the event of a malfunction in the system, for example if another line or a transformer fails.

To meet the N-1 criteria, the Salzburg line is being built as a dual-system line.

The Salzburg line consists of two three-phase systems. The structural arrangement of the individual phase conductors depends on the pylon design used. Either one phase conductor is located on each cross-arm of the pylon (“tons” pylon), or two conductors are located on the lower cross-arm of the pylon (“danube” pylon).

Each of the phase conductors consists of multiple sub-conductors, which form a bundle conductor. In the case of high-voltage and extra-high voltage transmission lines, the conductors are usually bundled into groups of three of four. For the Salzburg line, a three-bundle configuration was selected, meaning that each bundle consists of three separate conductors. Use of the three-bundle configuration also significantly reduces corona noise.

In addition to the conductors, an earth wire is attached to the top of the pylon to protect the line against direct lightning strikes. 

Two different pylon types are being used in constructing the Salzburg line: “danube” pylons with two cross-arm levels and “tons” pylons with three cross-arm levels.

The decision about which of the two pylon types will be used at a specific location depends mainly on whether the local topography is flat or hilly. Since danube pylons only have two cross-arm levels, they appear much more compact and are also lower in height than tons pylons. This is of significance when the terrain is mostly flat and offers widespread views.

Tons pylons appear slimmer on the whole due to their shorter cross-arms, but they are higher than danube pylons. However, the shorter cross-arms have the advantage that less surface area is needed, which is especially advantageous in mountainous regions where space is often limited.

Therefore, the natural terrain determines whether the danube pylon type or the tons pylon type can be better integrated into the landscape. A great deal can be done to minimise the visibility of power lines by making optimum use of the interplay between terrain and pylon type and the ability to “hide” the lines to a certain extent. The olive green colour of the pylons also helps to reduce their visibility.

However, it is not only the type of electricity pylon selected that determines how high the Salzburg line pylons will be at the respective locations. Local conditions play a large role here too. The most important factors are:

• the distance to be covered between two pylons
• the topography between the two pylons to be connected (e.g. hilltops)
• any obstacles between the two pylons to be overcome (other lines, rivers, roads, etc.)
• whether other lines are to be included (e.g. lines from Salzburg Netz GmbH).

As a rule, however, danube pylons are 48?metres high and tons pylons are 52?metres high. In addition to these two traditional pylon types, a new type of electricity pylon?– a “tubular” pylon?– is being erected along one stretch of the Salzburg line.