The transformers were transported from the Siemens factory in Nuremberg in Germany using a special trailer and then by ship to the port of Eemshaven. Yesterday the transformers were hoisted from the ship, placed on a trailer, and then driven to the COBRAcable construction site at Eemshaven.
Undersea electricity cable
COBRAcable is a cable connection with a capacity of approximately 700 MW. The cable is about 325 kilometres long and runs between Eemshaven (the Netherlands), the German part of the North Sea and Endrup (Denmark). The connection has been designed as a high-voltage direct current (HVDC) cable, because this DC technology reduces the losses in electricity transport over long distances, which means that virtually no renewable energy is lost. Two land-based converter stations, one in the Netherlands and one in Denmark, are needed to connect the cable to the Dutch and Danish transmission grid respectively. The cable is due to be operational in the second half of 2019.
The electricity (depending on the direction of transport) is converted from direct current to alternating current and vice versa in the converter stations. The transformer then ensures that the alternating current of the converter is adapted to the voltage of the Dutch grid (380 kV), so that the 700 megawatts that can be transported over the COBRAcable can be converted and connected without difficulty to the high-voltage grids in Denmark (400 kV) and in the Netherlands (380 kV).
The laying of the COBRAcable has an important role to play in the creation of a sustainable, international electricity market. The Netherlands and Denmark can use the cable to exchange green power in a simple, safe and environmentally-friendly way. More sustainable wind energy can be imported from Denmark, for example. At times when there is little wind in Denmark, the cable can improve the continuity of the electricity supply in Denmark.
Role of Siemens
As the supplier of the electrical plant, Siemens is also responsible for its installation in the converter stations in the Netherlands and Denmark. In the Netherlands, Siemens is also responsible for the civil engineering part of the converter station.
Other undersea electricity cables
The COBRAcable is not the first undersea electricity connection laid by TenneT. In 2008, TenneT laid the NorNed cable between the Netherlands and Norway (capacity: 700 MW, length: 580 km) and in 2011 the BritNed cable between the Netherlands and the United Kingdom (capacity: 1,000 MW, length: 260 km). In addition to the new COBRAcable, TenneT is currently working on the construction of NordLink. This undersea cable between Germany and Norway will have a capacity of 1,400 MW and is expected to be ready in 2020.
After arriving at Eemshaven, COBRAcable transformers were placed on a trailer, and then driven to the COBRAcable construction site.