Off the island of Baltrum, TenneT began connecting three offshore wind farms to the extra-high voltage grid in the summer of 2024. The new 525 kV DC connections of the 2 GW offshore grid connection projects BalWin3+4 and LanWin1 will strengthen the German power grid and increase the share of green electricity. The egeplast Power Protect PE-RT in 450 x 61.5 mm was used as a protective pipe – to protect the natural environment by means of horizontal directional drilling.
The three offshore grid connection projects BalWin3+4 and LanWin1 off the island of Baltrum with a total route length of 795 km, of which 530 are at sea, represented a further milestone on the road to supplying green electricity in the summer of 2024. The connection of the three offshore wind farms to the extra-high voltage grid strengthens the German power grid and is a further step towards the energy transition.
So-called grid connection systems are necessary for connecting offshore wind farms to the extra-high voltage grid. For the 2 GW offshore grid connection projects BalWin3+4 and LanWin1, the transmission grid operator TenneT carried out horizontal directional drilling from the land side of the dike to a working pontoon in the Wadden Sea in the summer of 2024. The grid interconnection points of these projects will be located in Unterweser and Wilhelmshaven. The 525 kV DC connections will strengthen the German power grid in the future. TenneT is building these DC grid connections with egeplast protective pipes for high and extra-high voltage cables up to 525 kV.
Horizontal drilling protects natural space
In the course of the realization of the grid connection systems via the Baltrum corridor, the flood protection systems, dunes and particularly sensitive areas (for example, seagrass meadows) in the area of the mainland near Dornumergrode and in the following years the island of Baltrum must be crossed at its eastern end.
In deviation from previous offshore projects, the projects of the 2 GW program (= transmission capacity) are being realized with a higher voltage of 525 kV. In these lines, a so-called “metallic return conductor” is also laid. Overall, one route consisting of three boreholes (positive, negative pole and metallic return conductor) is required per grid connection system for each crossing section.
As part of the offshore grid connection projects BalWin3+4 and LanWin1, routes are laid across the island of Baltrum to the mainland. In order to protect the sensitive Wadden Sea natural area and to ensure the safety of the dike, TenneT has decided to use horizontal directional drilling to cross under the island and the dike systems. The high-temperature-resistant egeplast Power Protect PE-RT in 450 x 61.5 mm is used for these horizontal directional drilling operations. It is a protective pipe for high and extra-high voltage cables up to 525 kV, which has increased thermal stability to withstand the high thermal loads. The combination of high flexibility and strength of the PE pipe used offers optimum properties for carrying out these horizontal directional drilling operations.
The total route length of BalWin3 is 245 kilometers, of which 200 kilometers are at sea and 45 kilometers on land. The route length of BalWin4 is 275 kilometers, of which 165 kilometers are at sea and 110 kilometers on land. The route length of LanWin1 is also 275 kilometers, of which 165 kilometers are at sea and 110 kilometers on land.
For the construction, a consortium (ARGE) consisting of the companies MATTHÄI Bauunternehmen GmbH & Co KG, MATTHÄI Wasserbau GmbH & Co KG, Bohlen & Doyen Bau GmbH and Beermann Bohrtechnik GmbH was commissioned by TenneT. The pipeline construction work is carried out on behalf of the ARGE by the companies MATTHÄI and Bohlen & Doyen.
High requirements met by egeFit®
Due to the limited working areas near the protective dikes, the dike foreland, and Baltrum Island, the required total lengths of the pipe strings were halved, and the two partial strings were connected before drilling using the egeplast connection technology egeFit® – “Golden Seam” connector. The long drilling routes did not allow for reductions in tensile forces, which led to the modification of the “Golden Seam” to prevent a decrease in tensile strength. The modified “Golden Seam” was integrated directly into the pipe string.
egeplast
Power Protect PE-RT
Protective pipes for high and extra-high voltage cables with a low-friction inner layer and individual marking.
UV-resistant signal color layer
Solid wall or co-extruded, optionally with stripes
Inspection-friendly inner layer: optionally highly slidable or abrasion-resistant
egeplast
egeFit®
Connection Technology “Golden Seam”
Seamless!
The modification of the egeFit® “Golden Seam” connection technology prevents a reduction in tensile strength. The “Golden Seam” is created through a specially developed integrated recess that automatically accommodates the inner bead. Subsequent removal of the weld bead is eliminated. This type of connection is particularly well suited for limited space conditions on the construction site, enabling the connection of longer pipe strings. The “Golden Seam” is available as a fully integrated solution for Power Protect pipe strings. As an adapter, the connector can be flexibly welded to any pipe end.
Project Data
Project description
525 kV DC cable / LanWin1; BalWin3 and BalWin4 connection of the offshore wind farms with the grid interconnection point in Unterweser or Wilhelmshaven
Challenges
Construction of a cable protection pipe system for a 525 kV extra-high voltage direct current transmission (HVDC) by connecting pipe strings > 600 m
Solution
Use of egeplast Power Protect PE-RT cable protection pipe system made of PE with increased thermal stability for high and extra-high voltage cables up to 525 kV in combination with egeFit® – “Golden Seam” connector with and without weakening factor.
Construction phase
2023 – 2030
Installation
Closed construction method (HDD)
Pipe system
10,632 m egeplast Power Protect PE-RT 450 x 61.5 mm
1,380 m egeplast Power Protect PE 280 x 38.3 mm
16x egeFit® – “Golden Seam” connector
450 x 61.5 mm; 2x egeFit® – connector
280×38.3 mm electrofusion couplers, loose flanges, additional accessories
Project participants
Client TenneT Offshore GmbH
Construction Matthäi Bauunternehmen GmbH & Co. KG, Matthäi Wasserbau GmbH & Co. KG, Bohlen & Doyen Bau GmbH, Beermann Bohrtechnik GmbH
