Transformer on its way back to sea

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The world's largest offshore wind farm is nearing the end of the long holiday forced upon it after a serious failure of its main transformer on June 9 put the plant out of action (Windpower Monthly, July 2007). Late last month the 140 tonne transformer, supplied by Italian company Tironi, was ready to be shipped back to the Rødsand facility in Denmark from an ABB factory in Drammen, Norway, where it had been taken for repair. At 165 MW, the Rødsand wind plant of Siemens 2.3 MW turbines lies a short distance from the town of Nysted off the south-east Danish coast.

A low voltage winding in the wind plant's transformer has been replaced after it was destroyed in a short circuit. The cause of the short circuit was "transient over-voltage," says team leader Jimmy Marcussen from the transformer platform's operator, local electric utility company SEAS-NVE. What caused the sudden voltage overload is the subject of debate between SEAS/NVE and the Italian supplier of the transformer. An evaluation is being undertaken by experts, not least because it is an insurance matter, says Marcussen.

Insurance is a hot topic with regard to the DKK 50 million (EUR 6.7 million) in lost income from sales of electricity during the downtime -- a matter for the wind farm's two owners, European energy companies DONG and E.ON, and their insurers.

Late last month, shipment of the transformer back to its offshore foundation was dependent on a weather window of two days without wind to allow for safe passage out of Oslo Fjord and across the Kattegat Sea to Denmark. Marcussen was hoping that the 72 Siemens turbines could be back in operation this month.

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