ABB Review Special Report - ABB - ABB Group

3Valve building in the Slupsk (Poland) converter stationof their lives and it is essential thattheir sense of direction remain unimpaired.Back in 1959 a study was carried outto determine how the Gotland cablehad affected the marine environment[2]. This was followed by exhaustivestudies on the Fenno-Skan link (Sweden–Finland)and the Baltic Cable(Sweden–Germany) [3]. The reportswere unanimous: marine life is affectedneither by the magnetic field nor byany chemical reactions. The facts speakfor themselves. Eels continue to findtheir way to the Baltic Sea, despitehaving to cross seven cables on theway [4, 5].eddy currents that flow in all powertransformers generate noise at a frequencyof 100 Hz. Converter stationsalso produce higher-frequency noisethat can be irritating to people livingnearby. It was clear that special soundproofingwould be necessary. Followingcalculations and measurement of thenoise level and noise propagation, thetransformers and reactors were enclosed.The filter capacitor cans are equippedwith a noise-reducing device.A magnetic field with minimal effecton the surroundingsWhenever electricity is transmittedthrough a conductor it generates amagnetic field around it. Since DC isused, the field is of the same type as theearth’s natural magnetic field. This iscompletely different to the AC fieldsnormally produced, for example,around overhead lines.Measurements have shown that the magneticfield around the cable at a distanceof six meters is equal in strength to theearth’s natural magnetic field, while at adistance of 60 meters its intensity dropsto just one tenth of that field.The magnetic field resulting from thecombination of 1 + 2 cables varies withthe depth and relative spacing of thecables. It is not practicable to lay thehigh-voltage cable at the same time asthe two return cables, which meansthat they cannot be laid right next toeach other. They also have to be separatedbecause of the heat they generate.In shallow water the HV cable islaid 5–10 meters from the returncables. The resulting magnetic fieldmeasured on the surface of the sea istypically 80% of that obtained around ahigh-voltage cable in a monopolarinstallation. The equivalent figure at100 meters depth with 20–40 metersseparation is typically 50%.Further away from the cables there isan even greater percentage reductionin the magnetic field, added to thefact that the absolute value of the magneticfield at this distance is insignificantcompared with the earth’s magneticfield. Thus, the use of returncables has no major effect on magneticfield strength. And, anyway, modernships no longer depend on magneticcompasses.But what are the possible effects onanimal life? Experience with previouscable links has shown that they donot affect fish or other marine organisms.Nor do they affect the vital homingability of eels and salmon. Thisis especially important since these fishmigrate regularly during the courseNo chlorine formationThe originally proposed monopolarsolution, which would have used electrodesto transmit the return currentundersea, has been replaced by analternative solution in which returncables form a closed circuit. Any concernsabout chlorine formation havetherefore been entirely eliminated,since no electrolysis can occur.34841 Conductor2 Conductor screen3 Insulation4 Insulation screen5 Metal sheathSwePol Link power cable, rated600 MW and 450 kV DC. Itsoverload capacity is 720 MW attemperatures below 20°C.1256796 Protection/bedding7 Reinforcement8 Armor9 ServingSpecial ReportABB Review59