Baltic Cable
The Baltic Cable is a HVDC power line running beneath the Baltic Sea that interconnects the electric power grids of Germany and Sweden.
The Baltic Cable uses a transmission voltage of 450 kV – the highest operating voltage for energy transmission in Germany. 250 kilometres (160 mi) long, it was the second longest high voltage cable on earth, until Basslink came into service in 2006. It is a monopolar HVDC system with a maximum transmission facility of 600 megawatts (MW).
Route
The course of the Baltic Cable starts in Germany at the inverter station at Lübeck-Herrenwyk, which is situated on the site of a former coal-fired power station. It crosses the river Trave in a channel 6 metres (20 ft) below the bottom of the river and then follows its course as sea cable laid at the Eastern side of this river. After crossing the peninsula at Priwall the cable runs at first parallel to the coast of Mecklenburg-Vorpommern, in order to turn behind Rostock north-easterly toward Sweden.
From the point on the southern coast of Sweden where it reaches land, the Baltic Cable runs for a further 5 kilometres (3 mi) as an underground cable. The last 12 kilometres (7.5 mi) of the 262 kilometres (163 mi) long Baltic Cable power line are built as overhead lines hung on 40 pylons.
Although the Baltic Cable is a monopolar line, which would only require one conductor on the pylons, two conductors were installed along the whole overhead section. These conductors are permanently connected in parallel in the inverter station at Kruseberg and at the termination of the overhead line.
Operation
Because this overhead line can generate radio interference, there is a highly effective active filter system installed at the Kruseberg inverter station. In the Lübeck-Herrenwyk inverter station, there is no requirement for such a system, because there is no overhead powerline section on the German side of the Baltic Sea.
The cable cannot be operated at the maximum transmission rating of 600 megawatts, because the 380 kV line which begins at the converter station of Lübeck-Herrenwyk ends at the Lübeck-Siems substation. From there power flows on 220 kV and 110 kV lines, which reduces the maximum transmission rate and increases the losses of the transmission.
Expansion schemes
Of the two originally planned 380 kV lines to Lübeck (from Krümmel Nuclear Power Plant to Lübeck-Siems and from Schwerin substation to Lübeck-Herrenwyk), the 380 kV line between Krümmel and Lübeck-Siems was canceled according to speakers from E.ON AG.
There is still the option to build a 380 kV line from Lübeck to another 380 kV substation in Schleswig-Holstein, Hamburg or Lower Saxony. The construction of the 380 kV link between Lübeck-Herrenwyk and Schwerin is not progressing due to opposition from ecologists.
A transmission rate of 600 MW should be possible via a new 220 kV cable and a static var compensator in Lübeck-Siems after 2005.