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Tacke Windtechnik has equipped all its TW 600 kW turbines with new brake valves in response to control system reports from several turbines of a malfunction. Before the retrofits were completed, though, a 600 kW turbine, at Anröchte Altenmellrich, failed to brake in high wind speeds, reports Tacke. The resulting centrifugal forces seriously damaged the turbine, which had not been retrofitted. According to the company, on the evening of January 19, during wind speeds of 17 m/s and when the turbine was operating with an average output of 630 kW, the grid went down. The turbine attempted to respond to an order to stop from the control system, but the brake system failed to bring the turbine to a halt. An independent report concluded that the signals in the safety system worked, but that the brake valves jammed, says Tacke. In the meantime all the TW 600 units have been retrofitted with new valves. "Malfunction of these valves is ruled out," says the company and stresses that the turbine runaway could not have been predicted as the problem lay in a brake valve production error.