The Baltic Cable uses 450 kV the highest operating voltage of all systems for transmitting power in Germany and was up to the commissioning of the NorNed in 2008 with a transmission distance of 250 km, the longest in Europe in use high-voltage cable . The transmission line is implemented as a high-voltage direct current transmission (HVDC) with a maximum transmission capacity of 600 MW.
With a submarine cable, the principle of monopolar direct current transmission is that only one pole is laid as an insulated cable in the ground or on the seabed.
The second pole is designed as an electrode in the water. The sea water or the upper layers of the earth serve as the return line on the sea route. In order to achieve a low earthing resistance , the earth electrodes are designed as large-area structures, the so-called electrodes . The electrical conductivity of seawater plays because of the large cross section of the resistance not matter. With the Baltic Cable , the electrodes of the earth electrodes consist of a ring made of bare copper with a radius of 1000 m.
Environmental aspects of the electrodes submerged in the water
In seawater, electricity is transported through ionic conduction . The electrolysis triggered by the maximum electrical direct current of 1340 A at the electrodes leads to chemical decomposition of the seawater or the salts dissolved in it. The chloride dissolved in the water is oxidized to chlorine at the anode , and the oxygen dissolved in the seawater is reduced to hydroxide ions at the cathode . 41 kg of chlorine at the anode and 47.8 kg of sodium hydroxide at the cathode are released into the Baltic Sea every day . At the same time, 6.6 g / min of dissolved oxygen is withdrawn from the seawater at the cathode. In the case of the Baltic Cable, the electrode in Sweden is the anode and the German side is the cathode. The direction of the current is always the same, regardless of whether power is transferred from Sweden to Germany or vice versa. In order to change the direction of the transmitted power, the voltage of the high-voltage cable is reversed, not the direction of the current. It is therefore possible to choose different materials for the two electrodes (anode made of titanium, cathode made of copper) in order to avoid corrosion in particular of the anode.
By further enlarging the surface of the electrodes, the release of chlorine and sodium hydroxide solution can be distributed over a larger amount of water and thus the concentration of the reaction products can be reduced through dilution. Although the affected area of the Baltic Sea increases with increasing distribution of the reaction products, the environmentally toxic effect within the affected area decreases according to the dilution of the reaction products. Since electrolysis is necessary to maintain electrical conduction (ionic conduction) through the sea water, electrolysis can only be completely avoided by a metallic connection between the two electrodes.
Alternatively, it can also be expanded to a bipolar system. After carrying out such an extension, if both poles were operated with the same strength of current, no current would flow through the grounding electrodes and thus no electrolysis of the seawater would occur. In fact, some monopolar HVDC systems have already been upgraded to bipolar systems (example: Kontiskan ). The overhead line section in Sweden has been prepared for this by installing two conductor cables, and at least on the area of the Arrie converter station in Sweden there is enough space for the erection of a second converter. Whether this expansion will take place in the foreseeable future, which could allow double the transmission capacity, is questionable because of the suboptimal network connection in Lübeck.
The Baltic Cable begins in a converter station built on the site of a former coal-fired power station in Lübeck- Herrrenwyk ( ). Immediately next to this station is a 110 kV / 10 kV substation operated by Netz Lübeck GmbH, which is installed on the masts of the 380 kV / 110 kV overhead line Lübeck-Siems - Lübeck-Herrenwyk . kV three-phase circuits is fed or via a 380 kV / 110 kV transformer on the area of the converter station in Lübeck-Herrenwyk.
The "Baltic Cable" emanating from the converter station, which consists of the 450 kV high-voltage cable and the electrode cable leading to the electrode in the Baltic Sea, crosses the Trave located directly next to this area in a channel 6 meters below the floor of the Trave then as a submarine cable laid in the Trave to follow it to its mouth.
After crossing the Priwall peninsula , the Baltic Cable follows the coast of Mecklenburg-Western Pomerania , then slowly to the northeast, east of Rostock , towards Sweden. The electrode cable leading to the electrode runs up to about 5 km northwest of Kalkhorst-Warnkenhagen , Mecklenburg-Western Pomerania parallel to the high voltage cable (distance approx. 1 meter, in the canal laid under the Trave directly next to the high-voltage cable).
At this point it branches off in an easterly direction away from the route to the electrode atlead. This is designed as a bare copper ring with a radius of 1000 meters off the German Baltic coast near Kalkhorst-Warnkenhagen. The 32-kilometer electrode cable is an XLPE-insulated copper cable. The first 20 kilometers of this cable calculated by the converter station in Lübeck-Herrenwyk have a cross-section of 1400 mm², the last 12 kilometers a cross-section of 800 mm².
From the landing point on the south coast of Sweden, the 450 kV cable still leads over a distance of 5.5 kilometers as an underground cable to a point east of the E6 at () Country. From there the overhead line runs over two masts to the first guy mast at ( ) in a north-northwest direction. At this mast the line changes its direction in a north-northeast direction and runs east past Södra Haslov over seven support masts to the next guy mast at ( ). Now there is a change of direction to the northeast. It goes over eight masts to the third guy mast at ( ).
Now the line swings in a west-north-westerly direction and leads over 15 masts (including 3 angled masts) south of Västra Ingelstad to the penultimate guy mast at ( station in Kruseberg ( ), which is also known as the Arrie converter station , and to an existing substation for 380 kV / 110 kV was added.). From this mast, the line runs over a support mast, an angled support mast and the end mast to the converter
In total, the 12-kilometer overhead line section consists of 40 masts, each with a traverse for two conductor cables. Two double-bundle conductors are used as conductor cables on the overhead line section, which are permanently connected to each other at their ends and are attached to the masts on 6 meter long insulators. Thus the overhead line of the Baltic Cable, although it looks like a bipolar line, is a monopolar line.
The 23-kilometer line from the Kruseberg converter station to the anode on the bottom of the Baltic Sea off the Swedish coast consists of two parallel-connected copper cables laid in the ground with a cross-section of 630 mm² each, insulated with XLPE . 40 titanium nets serve as the anode, each of which has an area of 20 m² and which are covered with plastic pipes and stones to protect against mechanical damage. Because of its construction as a monopolar cable, the Baltic Cable leads to significantly higher magnetic fields in its surroundings than DC cables with integrated or short-spaced return conductors.
Since this overhead line can cause radio interference, an active harmonic filter was installed in the converter station in Kruseberg . Because there is no overhead line section of the Baltic Cable on the German side, there is no such facility in Lübeck-Herrenwyk.
Bottleneck and network expansion
The HVDC Baltic Cable could not originally be operated with the maximum possible transmission capacity of 600 MW, as the 380 kV three-phase current line from Lübeck-Herrenwyk ends in the Lübeck-Siems substation and the connection to the German 380 kV network is still via lines the 220 kV and in some cases even the 110 kV level, which greatly reduces the maximum transferable power and also increases the transfer losses.
From the originally planned two 380 kV lines to Lübeck (from the Krümmel nuclear power plant to Lübeck-Siems and from the Lübeck-Herrenwyk converter station to the Schwerin 380 kV substation ), the construction of the 380 kV line between the Krümmel nuclear power plant and the According to E.ON AG , the Lübeck-Siems substation has been deleted. The construction of a 380 kV connection from Lübeck-Herrenwyk to Schwerin is also not making progress due to high spatial resistances .
A new 220 kV cable and a static reactive power compensator (SVC) in Lübeck-Siems have enabled a transmission capacity of 600 megawatts since December 2004. The reactive power compensation system was designed and built by Siemens.
Since the expansion of wind power in the network area of the Schleswig-Holstein Netz increased from five megawatts in 1989 to 6,450 MW in 2019, the need for additional transmission capacity within Schleswig-Holstein and towards the south has increased even further. With project number 42, an extra high voltage line between the Segeberg district , Lübeck, Siems and Göhl was laid down in the Federal Requirements Plan Act. Because of its course along the Schleswig-Holstein Baltic Sea coast , the transmission system operator Tennet TSO also refers to the line as the East Coast Line. It has a length of km 132, consists of three sections and is in parts as underground cables - pilot project to run. Total commissioning is planned for 2027 .
In the night from April 16, 2016 to April 17, 2016, the electrode cable on the Priwall peninsula was defective. This led to the development of hydrogen at the damaged area because the defective electrode cable acted like a cathode at this point, where this gas was created. As a result of the heat generated by the defect, it ignited explosively when its concentration in the air was sufficient and generated a 3 meter high jet flame. Because there was no device to monitor the electrode cable, no alarm was triggered by the operators. The called fire brigade could not extinguish this at first, but the flame went out when the cable was switched off because no more hydrogen was supplied.
- Baltic Cable AB
- From FOCUS No. 43 (1993): Bathing in caustic soda
- from Greenpeace magazine 1.98: "Rust damage on poison gas ammunition: underwater power cable in the Baltic Sea has unexpected side effects"
- ABB Group: Baltic Cable HVDC Project. Retrieved April 4, 2011 .
- FOCUS No. 43 (1993): Bathing in caustic soda
- 30 years of wind power in Schleswig-Holstein - from almost 50 to more than 3,000 systems. Schleswig-Holstein Netz , April 24, 2020, accessed on June 25, 2020 .
- BBPlG, project 42: Segeberg district - Lübeck - Siems - Göhl. Federal Network Agency , accessed on June 25, 2020 .
- East coast line. Tennet TSO , accessed June 25, 2020 .
- Katrin Diederichs: Jet flame from the depths: Baltic Cable explodes on the Priwall . LN-Online.de (portal of the Lübecker Nachrichten). April 18, 2016. Retrieved January 16, 2019.
- Repair work on the Baltic Cable completed . Statkraft Markets GmbH. April 26, 2016. Retrieved January 16, 2019.