Three companies based in Germany's traditional heavy engineering Ruhr district have developed a novel electromagnetic braking system dubbed "the retarder" and a synchronous, permanently excited generator for a gearless wind turbine which thus needs no power from the grid to start operating. A patent has been granted to designer Franz Mroz for the retarder by the European Patent Office. It has specially dimensioned electromagnets directly connected to the generator. As the generator turns, eddy currents induced in the retarder become more powerful, exerting a force in the opposite direction and braking the machine without wear -- a system similar to that used on electric trams. Following testing on a 20 kW machine for two years, a Mroz 80 kW prototype is due to be installed in the autumn. The companies involved are Franz Mroz Umweltfreundliche Energiesysteme of Dülmen, Elmo based in Bocholt and Halterner Maschinenbau in Haltern. Mroz says the machine will be 10-15% more efficient than turbines with gearboxes. A 35% subsidy was granted under the Arbeitsgruppe Industrielle Forschungseinrichtung (AEF).
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Senior Renewable Energy Analyst (WindGEMINI Product Lead) DNV GL Bristol (City Centre), City of Bristol