Danish – Swedish cable has been fixed
A 24 test was concluded on Thursday. The 400 kV cable between Denmark and Sweden, which has been out of function since January 8 2019, is thereby ready for operation. The reason for this was that cable was leaking oil and the hole was not easy to locate.
The 35 year old cable was declared ‘out of function’ when it was discovered that it leaked oil. Oil is part of the insulation in cables from back then, and although the oil is as thin cooking oil and dissolves over time, it is not considered acceptable for it to leak into the waters. That is why Danish company Energinet immediately began to collect the oil and try to find the leak by the use of divers and several ships in Øresund.
The damage was difficult to spot, since the oil was leaking from other areas than where the hole to the insulation had started. From the hole, the oil flowed under the cables protective outer sheath before it began to leak. Oil was found several kilometers from where the it was presumed that the damage had been done to the cable. It therefore took a long time before the error was found 1.32 kilometers from the Danish coast.
The submarine cable was lifted from seabed to the ship H.P. Lading several time, where part of the cable was frozen so the oil could create an ice plug. By doin this, experts were able to determine on which side of the ice plug the pressure fell because oil was leaking. By using this method, the flaw was found after freezing parts of the cable.
It turned out that 26 meters deep in the waters there was an approximately 1.5 cm long crack in the lead cap of the cable, which holds the insulation oil in and keeps salt water out. Some of the steel bands placed around the lead cap to seal it were broken, and it is possible that they created a hole in the lead cap.
The cause of the damages have not yet been determined. The defect parts will be examined further at a laboratory, Energinet have never experienced this type of fault in a submarine cable. Normally, damages to submarine cables happens when an anchor or some sort of similar device strikes the cable, or if short circuit happens because of something is wrong inside the cable.
The cable was repaired on February 15, and on February 20, voltage was again put on. Since there were no faults after 24 hours, the cable is able to return to service. Although, the cable will have to be placed in the seabed in order to be protected before resuming to operation.
Source: Energinet.dk / Maritime Danmark