Eckhardt Rummler, director of E.ON's electricity generation business, said installing the transformer is a prerequisite to connecting the wind farm to the mainland on schedule.
Amrumbank West will have a peak capacity of 288 megawatts, enough to meet the yearly energy demands of 300,000 households. E.ON said the project would be finished by 2015 and reduce carbon emissions by more than 740,000 tons per year.
E.ON since 2007 has invested more than $13 million on renewable energy and is Germany's third-largest operator of offshore wind farms.
"From planning to installation, this was a significant engineering achievement, one that affirms our position as a global leader in offshore wind," Rummler said in a statement.
Germany aims to use renewable energy for 80 percent of its energy demand by 2050.