Status of 380-kV Berlin diagonal power link

Necessity

There is already a 380-kilovolt (kV) diagonal power link running across Berlin, from Spandau over Mitte to Marzahn. It is the central artery that supplies the capital with electricity. The line is becoming even more important for the regional transfer of electricity, though.

Given the growing generation of wind, solar and biomass power in Mecklenburg-Western Pomerania and Brandenburg, the load on the line keeps increasing. Moreover, the older sections in the western part of the power link need to be renovated with increasing urgency.

All this means that a renovation and reinforcement of the current power link is necessary. Parts of the power link in the east have already been renewed. By 2024, another new section of the 380-kV Berlin diagonal power link should be put in service.

Line route

The section of approximately 4.2 kilometres planned for the modernisation connects the substation of Charlottenburg in the Darwinstraße with the substation Mitte in the Bissingenzeile near Gleisdreieck. The entire 380-kV diagonal power link runs underground for the most part, from substation Teufelsbruch in the west to substation Marzahn in the east of the city. Substations along the section lower the line voltage to 110 kV and deliver the power to the connected Berlin distribution system.

Today, the section to be modernised uses single-conductor oil-filled cables in underground pipes. The cables are cooled by the water running through the pipes. This technology has been tried and tested but the line capacity is no longer sufficient to meet the higher requirements. Due to the increasing load and the correspondingly high heat development, the outage potential has grown.

For the construction of the new section, 50Hertz will install a new cable system in an accessible and therefore maintenance-friendly tunnel between substations Charlottenburg and Mitte.

Tunnel construction

The new part of the 380-kV Berlin diagonal power link will run through a tunnel. This tunnel, with an inner diameter of three metres, should run about 15 to 30 metres beneath the surface. It will be created underground using a tunnel boring machine, a method used successfully worldwide. After drilling, the tunnel is lined with concrete wall elements (Tübbingen).

From the outside, only three shaft structures are visible along the link. An integrated tunnel rail makes easy inspection and maintenance possible. It can also be used to transport material or, in case of an accident, injured persons. If the capacity demand continues to rise, a second cable system can be installed in the tunnel.

Since 1998 and 2000, two similar tunnels have already been in service in the eastern part of the diagonal power link between the substations Mitte and Friedrichshain as well as between Friedrichshain and Marzahn. The concept of a cable tunnel within a city has proven to be successful. A tunnel protects the Berlin cityscape, effectively shields the electric and magnetic fields and enables operation and maintenance without affecting street traffic.

Authorisation procedure

For the 380-kV Berlin diagonal power link, transmission system operator 50Hertz is currently applying for a number of individual approvals from the federal and state authorities as well as the competent district offices in Berlin. This includes permits under relevant sectoral laws. Water law conditions such as environmental protection and respecting the traffic code are closely evaluated.

In the first stage, 50Hertz intensively surveys the soil conditions along the planned tunnel route in coordination with the competent authorities.

The permit is granted when construction sections have been determined and analysed. The actual tunnel construction should begin in 2018 at the earliest, after the successful conclusion of these preliminary works. The commissioning of the new cable circuit is planned for late 2024. According to the plan, the old cable will remain in place for the time being as an additional fail-safe for the security of supply.