Case Study 1: Use of Cables in Areas of Outstanding Natural Beauty

The Denmark Aalborg - Aarhus line/cable is a classic example of the use of cables to protect areas of outstanding natural beauty.

To reinforce the 400kV network in the western part of Denmark, Eltra built a 140km link between Aalborg and Aarhus. The line, with a capacity of 1200MW, is mainly overhead but is buried in three sections in areas considered to be of scenic or ecological interest:

1. Southwest of Aalborg, a 7km section was put underground in an urban area but also one of historical significance.
   
2. Further south, the 150kV overhead line that crosses the Mariager Fjord was dismantled and 2.5km of 400kV and 150kV cable was laid.
   
3. Still further south, a 4.5km section passing through the Gudena Valley was placed underground as OHL was not considered appropriate through a picturesque area of lakes and wooded hills.

The cables used were aluminium with a conductor size of 1200 m2 and were arranged in a double circuit in a trench at a depth of at least 1.2 meters.

The total cost of the project was around €140m. The underground part represents about 10% of the total length and is estimated to have cost €35m (25% of the total). The project took 11 years of political negotiations, but only one year to engineer and two years to construct.