T&D World Magazine

Cables Across the Oslo Fjord to be in Full Operation From June

Statnett will start work on repairing the last of the faults on the Oslo Fjord cables on March 2. The repairs, which will be carried out by cable fitters in the company Nexans, will be in progress for a period of three months. By June 1 at the latest Statnett anticipates that all cable connections across the Oslo Fjord will have been repaired and back in operation at full capacity.

As a result of faults and fault repairs, the transmission capacity for power from South Norway to Sweden will be limited up to the end of May, and is estimated to vary between 200 and 1000 MW. According to plans, from June 1st normal capacity of 2050 MW will again be reached from South Norway to Sweden.

It was in the spring of last year that faults occurred on two of Statnett’s three connections across the Oslo Fjord. This resulted in reduced trading capacity with Sweden, and for some periods, reduced power prices in South Norway. At no time have the faults had any impacts on the supply security of electricity for Norwegian consumers.

This situation has been exceptional, with five simultaneous cable faults and oil leakages on two different connections across the Oslo Fjord. We have already implemented measures to prevent similar faults from having such long-term and unfortunate consequences for the market. This entails immediate acquisition of reserve cables, and in the long term, more detailed analyses will uncover other possible measures, says division manager Vibeke Hodne in Statnett.

The period of repair of the cable connections across the Oslo Fjord has been unacceptably lengthy. In addition to the exceptionally large extent of the repair works, mines were found along one of the cable routes; parts of the work have to be carried out in a very busy shipping lane, at depths close to 300 m; the cable installations are technically complicated and special, and in a competitive cable market Statnett has not been given priority ahead of others to the extent requested. In the event of an “ordinary” cable fault, cable fitters are needed to splice a cable – and in Statnett’s experience these have always been available. To splice a cable is one of the critical work operations, and it takes at least five days to carry out such an operation in the Oslo Fjord. There is usually a need for one or two splices, while the repairs of the cables in the Oslo Fjord have required nine splices, and five of these have been offshore. This has caused problems for the capacity of the supplier.

In addition, the outer stretches of the Oslo Fjord are very exposed to rough weather, something that makes the extensive repair works complicated. It is imperative that repair of such oil pressure cables is successful at first attempt. If it is not a success, the installation may be lost, resulting in an outage of several years until a new cable installation can be produced and installed.

Statnett has not deemed it justifiable to make any attempts to carry out repairs during the winter season, as the power system and the supply security would be jeopardized during the execution of the actual operations.

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