Siemens Power Transmission and Distribution (PTD), Erlangen, Germany, has connected the “Fehmarn Mitte” wind farm to the 110-kV high-voltage system on the Schleswig-Holstein mainland of Northern Germany following modernization and upgrading of the farm’s capacity. This represents a large portion of Germany’s currently biggest wind power repowering project, which will ultimately have a total capacity of 130 MW (150 MVA). By the next years, 120 obsolescent wind turbines on Fehmarn are to be dismantled and replaced by about 70 new machines of higher capacity. Up to now 27 obsolescent turbines were dismantled.

As part of the repowering project, which covers all the wind farms on the German island of Fehmarn, the operator of the Fehmarn Mitte wind farm replaced its existing 35 wind turbines of 225, 250 and 500 kW capacity with 25 new 2.3-MW turbines and optimized the power transmission system. As a result, this wind farm now has a maximum capacity of 57.5 MW, of which 46 MW have been connected up to the 110-kV system. Siemens not only delivered the necessary high-voltage substations, transformers, protection and control systems and medium-voltage components for the entire project, but also drew up the network study and played a key role in developing the connection concept.

Siemens erected the 110/30-kV Bisdorf substation in the geographical center of the island, close to the wind farm, to concentrate and transmit the power generated by the farm. The substation is connected to the 110-kV Göhl-Wind substation on the mainland via a 31-kilometer (19-mile) long 110-kV cable, including a 1.5 kilometer (1 mile) undersea cable under the Fehmarnsund. An isolating transformer at the Göhl-Wind substation isolates the wind farm system electrically from the transmission network. An 800-meter (1/2 mile) long 110-kV cable links the Göhl-Wind substation to the Göhl substation, where its capacity is ultimately fed into the 110-kV system of E.ON Netz GmbH.