The company said it had launched an investigation into the causes of the failure. Cameras are being sent in remotely to investigate the cause, but the project is not expected to be back online this week.
Lillgrund is located in Öresund, the strait between Denmark and Sweden. It is Sweden's largest offshore wind farm and came online in December 2007. It comprises 48 Siemens SWT-2.3-93 turbines.
In a Vattenfall document detailing the installation work, the company said it had problems deploying the cables, especially the export cable.
Linking offshore wind farms to the shore is one of the biggest challenges to the sector. There is already a high number of claims resulting from damaged subsea cables.
Past examples of issues include insufficient protection against the current or poorly implemented erosion protection damaging the cables.