Anholt Cable defects

In: Windfarms
23/02/2015
A cable fault is preventing transmission of power from the Anholt offshore wind farm to the onshore grid, The fault meant that the islanders lost power for 31 minutes before the emergency supply was up and running, and also that it is not possible to transmit the power being generated by the wind turbines to shore.

It is yet too early to say anything about the cause of the fault, but over the weekend Energinet.dk and its partners located the fault, which is affecting the sea cable close to the offshore transformer platform connecting the wind turbines and the sea cable.

There is nothing to suggest that the fault has been caused by a ship or an anchor.

Two vessels are currently preparing to start doing the repairs. One vessel will carry out the water-jetting procedure to expose the cable which lies protected in the seabed. The other vessel will raise the cable to the surface and make the necessary repairs.

- Repairing sea cables is far more difficult and also far more time-consuming than repairing cables on land. We expect the repairs to take approx. three weeks. However, as we need two periods of reasonably calm weather lasting several days, it may be more than three weeks before the wind farm will again be transmitting power to shore, says Per Hylle, Head of Department – Maintenance Jutland, Energinet.dk.

The Anholt cable was also hit by a fault last year. On 30 September, the onshore part of the power cable short-circuited. This resulted in the cable being out of operation for seven days.

Energinet.dk has therefore had to pay compensation in the amount of DKK 9,167,090.95 to DONG Energy, the owner of the wind turbines, for loss of profit during the seven-day period. The compensatory amount was based on wind data and market prices; in other words, what the wind turbines would have generated and earned.

The part of the cable which short-circuited has since been examined by a laboratory. Part of the cable was destroyed by the high temperatures produced, and it is therefore not possible to say exactly what caused the fault. However, it may have been caused by a fault in the insulation of the cable – either during the laying of the cable or during production of the cable.

The bill for identifying the fault and replacing the damaged part of the cable came to approx. DKK 1.5 million.

The sea cable was supplied by NKT Cables, while the land cable was supplied by Silec Cable.

Back in February 2013 some of the cable was unable to be buried to the depth needed, therefore rock dumping was used.

This is not the first time that the project has been troubled by cable failure. ​Back in Ocober it was announced that earlier cable problems had just been repaired.   This was due to a failure that occurred Thursday 30 September at 8.35. This was due to a short circuit found on the part of the cable buried a few kilometres west of the town Grenå. The failure was in a relatively small, limited part of the cable, but in order to make the most appropriate repair, a larger piece of the cable, approx. 20 metres, had to be cleared, cut off and replaced by a new piece of cable.  

The reason beyond those given then were not fully understood as there was a need for further investigations by the supplier in order to precisely clarify what caused the failure.  Costs for that repair were not given however it was understood that Dong Energy were compensated for losses to the tune of €1.2million

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