Grid project Bassecourt – Mühleberg

Overview

The planned decommissioning of the Mühleberg nuclear power plant from 2019 will result in the removal of a large part of the energy feed-in at the 220 kV grid level in Mühleberg. To ensure security of supply in the Greater Berne area, the missing energy must primarily be imported via Northwest Switzerland. To do so, Swissgrid is modernising and reinforcing the grid infrastructure. It is increasing the voltage of the transmission line between Mühleberg (BE) and Bassecourt (JU) from 220 to 380 kV and installing a transformer in the Mühleberg substation. The Bassecourt – Mühleberg extra-high voltage line, with a length of 45 kilometres, was already approved for an operating voltage of 380 kV by the Federal Inspectorate for Heavy Current Installations (ESTI) in 1978, but is currently only operated at a voltage of 220 kV.

Construction measures on pylons and the line

The future operation of the line at a voltage of 380 kV requires construction measures to ensure compliance with the applicable limit values for the electric field as well as the Ordinance on Electric Lines and Cables. The grid project's impact on the environment and the landscape are minimal. The noise emissions are below the target figures specified by law. This ensures that the most stringent statutory precautionary values pursuant to the Noise-Protection Ordinance (LSV) are observed.

Project

The Bassecourt – Mühleberg extra-high voltage line, with a length of 45 kilometres, was constructed in 1978. It was approved and set up for an operating voltage of 380 or 220 kilovolts per circuit. Since then, the 380 kV circuit has been operated at 220 kV and the 220 kV circuit has been operated at 132 kV. The circuit operated at 220 kV will be upgraded for a power transmission of 380 kV. This will occur in compliance with the applicable limit values in the Ordinance on Protection against Non-Ionised Radiation (NISV) as well as the Noise-Protection Ordinance.

The increase in voltage will not impact on the landscape. The increase in voltage and modernisation of the line will take place on existing pylons. The line's route will remain the same. Construction work will take place on 54 of the total of 142 pylons.

New transformer in the Mühleberg substation

The planned decommissioning of the Mühleberg nuclear power plant (KKM) by no later than 2019 and the corresponding withdrawal of up to 370 MW of feed-in at the 220 kV level at the Mühleberg site results in an additional import requirement to supply the Greater Berne area and Central Switzerland. As a replacement, Swissgrid is planning to install an 800 MVA 380/220 kV transformer in Mühleberg. Connection to the 380 kV grid is expected to occur via the existing Bassecourt – Mühleberg line, which is currently operated at 220 kV. This will also relieve the burden on the transformer in Bassecourt, which could not be operated safely without a line increase in Mühleberg (n-1). The tense energy and grid situation in the winter of 2015/2016 clearly illustrated the urgency of the feed-in into the 220 kV grid, including in the region of Berne.

People & environment

Noise

• The increase in voltage in a transmission line from an operation at 220 kV to 380 kV results in an increase in the maximum electrical field strength of the overhead line, which results in an increase in the noise level on the line.
• The planning figures, i.e. the most stringent statutory precautionary values in accordance with the Noise-Protection Ordinance (LSV), are complied with at all noise-sensitive areas operating at 380 kV.
• The existing quadruple conductor is currently already reducing the noise level along the line. The precautionary principle specified by the Noise-Protection Ordinance is therefore largely taken into account.
• The noises are caused by the corona effect, which primarily occurs during wet weather conditions (rain, snow, fog). The noises are barely perceptible in fine and dry weather.

Electromagnetic fields

• Magnetic fields
  
  • The emission limit for a magnetic field of 100 microtesla is complied with in all places where people may be present.
  • The optimum phasing is determined for the different sections in the project. The phase difference is already optimised in the section between Mühleberg and Pieterlen. The phase difference will be optimised for the section between Pieterlen and Bassecourt, which will result in an improvement from the current condition.
• Electric field: The increase in voltage to 380 kV will also lead to an increase in the line's electric field. The emission limit (IGW) of 5 kV/m is complied with at all points.