The enhancement of the Bassecourt – Mühleberg extra-high-voltage line is part of the «Strategic Grid 2025». Swissgrid needs the 380-kV connection between Bassecourt and Mühleberg to ensure the security of supply in the medium-term. This is particularly important in the winter months, when Switzerland relies on additional energy imports.
The decommissioning of the Mühleberg nuclear power plant will result in the removal of part of Swiss energy production in Central Switzerland from the end of 2019. In the medium-term, this missing feed-in needs to be offset by higher production by Swiss power plants or energy imports from abroad. To enable the additional imports, the existing capacities of the extra-high-voltage lines and transformers between Bassecourt and Mühleberg need to be expanded. This is particularly important in the winter months, when Switzerland relies on additional energy imports.
In a normal supply situation, Greater Bern will receive an adequate supply of electricity even after the decommissioning of the Mühleberg nuclear power plant. In the event of short-term grid congestion, the Swissgrid grid control room can take various measures, such as switching operations or interventions in electricity generation (redispatch) or measures on the power market (NTC adjustments), to respond to the situation and ensure grid stability. Swissgrid needs the 380-kV connection between Bassecourt and Mühleberg to ensure the security of supply in the medium term.
The Bassecourt – Mühleberg extra-high-voltage line is 45 kilometres long and was built in 1978. The Federal Inspectorate for Heavy Current Installations (ESTI) approved the line for an operating voltage of 380 kV back in 1978. However, it has been operated with a voltage of only 220 kV since that time. The voltage increase will take place in compliance with the limits specified in the Ordinance on Protection against Non-Ionising Radiation (NISV).
The line will be modernised along the existing pylons and will not change the landscape. In total, construction work is planned on 56 of 142 pylons as well as on the guyed gantries of the two substations in Pieterlen and Bassecourt: individual pylon foundations will be reinforced, double anchor chains will be installed, or the cable winch tension will be increased. The future operation at 380 kilovolts will result in an increase in noise emissions that will be hardly noticeable.
The construction costs for the increase in voltage and modernisation of the Bassecourt – Mühleberg extra-high-voltage line amount to approximately 11 million Swiss francs.
Schedule
On 22 August 2019 the Swiss Federal Office of Energy approved the voltage increase of the extra-high-voltage line between Bassecourt and Mühleberg from 220 to 380 kilovolts and dismissed the objections. These generally related to the load from magnetic fields and the noise or demanded that the line route be relocated or cabled. Various appellants have appealed to the Federal Supreme Court against the decision made by the Swiss Federal Office of Energy. The Federal Supreme Court confirmed the planning approval for increasing the voltage of the Bassecourt – Mühleberg line, rejecting all complaints, on 23 March 2021.
Swissgrid is carrying out the construction work in two stages. The first work on the section between Pieterlen and Bassecourt will begin in mid-August 2022. The existing mast foundations will be reinforced on four masts. In September, double supporting chains will be installed for around two weeks. At the beginning of September, the foundations of two pylons on the section between Mühleberg and Pieterlen will be reinforced. After an autumn/winter break, Swissgrid will carry out the remaining construction work in 2023. Swissgrid is planning to increase the voltage of the existing extra-high voltage line between Bassecourt and Mühleberg from 220 to 380 kV by the end of 2023.
Swissgrid has commissioned a new transformer in the Mühleberg substation. Together with the increase in voltage of the extra-high-voltage line, the transformer in Mühleberg will ensure that current can be transported with a voltage of 380 kV as well as 220 kV.
The last of four transformer poles was delivered to Mühleberg in mid-September 2020. The new transformer was transported from the port Auhafen in Basel to Mühleberg in four heavy-load transporter trips. Every transformer pole has a transport weight of 170 tonnes and is around 11 metres long, almost 3.6 metres wide and 4.5 metres high. The transformer has been operational since the end of 2020.
The renovation work for the new 380/220 kV phase-shifting transformer in the Bassecourt substation has been completed. The new transformer has been in operation since May 2020 and enables better control of the energy flows from France.
In the time window from 8 September – 31 October 2021, Swissgrid put the transformer in Mühleberg into operation for 25 days for test purposes. The voltage of the existing line between Bassecourt and Mühleberg was temporarily switched from 220 kV to 380 kV. The aim of the test operation was to test the coupling transformer in Mühleberg prior to final commissioning so that any defects can be identified and rectified in good time.
