Readings from conventional weather vanes mounted on the rear of the nacelle are affected by turbulence from rotating blades, says SAINCO's José Pinilla. Precise readings can only be made when the turbine is closed down. This means there is always a slight margin of error in yawing operating machines optimally into winds. Not only does this affect production but it also means that turbines suffer more structural stress than necessary.
Velflex consists of a laser diode situated internally at the top of the tower which projects onto a screen -- or projection window -- at the bottom. A camera reads the projected information: the degree of shift in the position of the laser projection together with the spectrum of frequencies created by various vibrations within the structure. Readings are taken periodically and the information is processed in real time. The degree and position of shift indicates the force and direction of tower flexion, which is directly related to wind force and direction.
Velflex's spectral analysis system also enables identification of vibration from all parts of the turbine -- including tower sections, blades and low and high speed shafts. If readings indicate the turbine is operating in unduly stressful conditions, then Velflex automatically alerts a control system.
Pinilla claims that Velflex can provide fingerprint frequency models not only for operational performance but also to optimise wind turbine construction. He says a whole range of variables can be established spectrally, including the density of turbine foundations and the torque applied to bolt joints. He foresees that Velflex will also be applied to offshore plant where stress on platform structures and turbines, mostly due to waves and currents, are largely unknown quantities.
SAINCO's claims regarding Velflex performance are, to date, based on a prototype application in an A300/330 kW turbine from Spanish parent company and electricity plant giant, Abengoa. The turbine is situated in the Tahivilla plant, Galicia region, developed by sister company DESA. Velflex won first prize for "most valuable innovation" at the European Wind Energy Conference in Copenhagen in July.