The pylons of the 380 kV line from Mettlen via the Lukmanier Pass to Lavorgo were constructed in the post-war years out of pipes of the allies' former supply pipeline, as a result of the shortage of raw materials. These pipes were filled with concrete to improve stability. Soon after they were erected it became clear that this form of construction tends to corrode from the inside. For that reason at the end of the 1990s Alpiq decided to replace some pylons on the existing route that had been particularly weakened by corrosion. At the end of 2001 Alpiq modified this strategy and submitted a planning approval application for the total renovation of the Ingenbohl – Mettlen section of the 380 kV Amsteg – Mettlen line. The majority of the line has now been renovated. Three sections – Küssnacht am Rigi (SZ), Lauerz (SZ) and Eyschachen (UR) – are still pending in the planning approval process.
As of 3 January 2013 Swissgrid assumed ownership of Switzerland's entire 380/220 kV transmission grid. The former owners – including Alpiq – transferred all existing lines and substations, as well as the projects started at network level 1, to Swissgrid. So since that date the Amsteg – Mettlen and Mettlen – Plattischachen lines have been in the ownership of Swissgrid. Planning, construction and maintenance of all lines and substations are now carried out by a single agency.
Küssnacht am Rigi section
In 2011 the Federal Court ruled that a feasibility study was to be produced for the 380 kV Amsteg – Mettlen line, for partial underground cabling in the municipality of Küssnacht am Rigi. Swissgrid submitted the requested cable study to the Swiss Federal Office of Energy, expressing the opinion that the partial underground cabling – as demanded by the Federal Court – was justifiable neither on the basis of visual effect nor of economy.
In 2011 the Federal Administrative Court ruled that a feasibility study was to be produced for the 380 kV Amsteg – Mettlen line for partial underground cabling in the municipality of Lauerz. Following the transfer of ownership, Swissgrid took on this task and had the cable study produced.
Following the landslides in the Windegg – Ober Rüti region in 2013, emergency pylons had to be produced for both 380 kV lines. The «Teilverkabelung Lauerz» feasibility study, [Partial underground cabling, Lauerz] which had already been produced, had to be revised. The results of the geological investigations which were carried out by GEOTEST on behalf of the Canton of Schwyz were also taken into account, and the requirements of ESTI relating to the «Erdbebensicherung der elektrischen Energieverteilung in der Schweiz» (Earthquake-proofing of electrical energy distribution in Switzerland), which is to be found in the draft consultation document, were included in the study.
After examining these new basic conditions Swissgrid has come to the conclusion that the subsoil in the landslide-prone region is suitable neither for an overhead line nor for underground cabling, so the «Durchstich Urniberg» (Urniberg transit), which is the subject of the study, is not feasible. The line can no longer follow the existing route and will have to be relocated.
The alternative line route along the lake, also indicated in the cable study, is judged by Swissgrid to be unfeasible for reasons relating to the effects on other infrastructure elements (roads, factory power lines, etc.). The implementation of this line route would result in the considerable obstruction or even total blockage of the main road from Lauerz to Schwyz.
In this section the parallel 380 kV Gotthard line runs on the uphill side. It is exposed to the same risk of landslide and for that reason is to be integrated into the existing project.
Eyschachen near Altdorf section
The 380/220 kV lines (Swissgrid) and the 132 kV of SBB will be bundled in Swissgrid Mast 9429/SBB Mast 60 section in the SABA Attinghausen area up to Swissgrid Mast 9440a/SBB Mast 81 in the Giessenkanal area with a total length of around 4.7 km to form a new route, running parallel with the motorway and the Reuss.