The two earth cables between Sogn and Ulven, which date back to the 1950s and 60s, need replacing. A lot has happened to roads and residential areas since the cables were installed 60-70 years ago. The route that was chosen back then is not suitable for the new cables.
Statnett is conducting thorough assessments to find the best solution for installation of new cables, either in a trench or tunnel. In the overall assessment, we will also take into consideration any inconvenience that the construction work will cause for residents on the section between Sogn and Ulven substations. What we do know is that a lot is buried in the ground in this area. This means it could be challenging to install the cables in a trench.
"In the event of a licence application for cables in a trench, at least one new route would be necessary. This is because the old cables must be operational and supply power while Statnett is installing the new cables," says project manager Kjell Rønningen.
To obtain more information about the soil conditions in the area, we will conduct test drilling between Sogn and Ulven both in 2015 and 2016. This work will continue until we find we have sufficient information about the conditions. Most likely, we will finish the work some time in 2016.
"Test drilling determines the depth to solid rock, which is important for planning a potential tunnel. However, if we drill at a location it does not necessarily mean there will be a tunnel under it later on."
A small drilling rig is used for the test drilling to drill a hole of approximately five centimetres in diameter. The hole is filled in again afterwards.
In connection with the assessment work, we also need to conduct seismic measurements in some places. The purpose of seismic measurements is to determine the depth to solid rock, the type of uncompacted material and the thickness of subsurface layers, as well as the quality of the rock. Combined with test drilling, seismic measurements provide a good picture of the subsurface rock formations in an area.
After the assessment work has been completed, Statnett will apply for a licence from the NVE for the Sogn-Ulven interconnector. As part of the NVE's licensing process, a consultation will take place, where all affected parties will have an opportunity to provide comments. Licences for the energy sector are considered in accordance with the Norwegian Energy Act.
The current owner of the Sogn-Ulven cable interconnectors is Hafslund Nett AS. Once installed, the new interconnectors will become part of the main grid and be owned by Statnett SF.