Blade retrofit work on entire series

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Retrofit work in Germany on the blades of 60 Tacke 600e wind turbines is to start this summer. The retrofit is to prevent edgewise vibration of blades, a known phenomena in the wind industry on stall controlled turbines with blades of around 20 metres. The vibrations have caused blade cracks on turbines from different manufacturers (Windpower Monthly, February 1998).

Tacke Windenergie declines to specify the solution it is adopting, but says it is different from the stall strips employed by Danish blade supplier LM Glasfiber to cope with the same problem (Windpower Monthly, May 1997). Tacke's Norbert Partmann says the retrofit involves "a small aerodynamic change," costs a few hundred D-Mark, and takes about one-and-half days using a crane. On the one third of turbines under guarantee Tacke is paying for the retrofit. On the others, from before the old Tacke's bankruptcy, the owners are paying.

Blades for the Tacke 600e turbine have in the past been supplied by Abeking and Rassmussen in Germany and the one time Canadian blade manufacturing arm of Tacke. Problems have occurred intermittently over the past two years on Tacke 600e turbines with blades from both manufacturers. In the future blades will mainly be supplied by LM Glasfiber, says Partmann. Abeking and Rassmussen is no longer a supplier.

Germanischer Lloyd (GL) has assisted with analysis of the blade problems. In September Tacke and GL reported that of the 1365 blades on TW 600 machines then in operation, 11 had been damaged. Only blades on the TW 600e were affected. The rotor diameter of the TW 600e, at 46 metres, is three metres greater than the TW 600. "Hidden flaws or manufacturing faults could not be deduced from the investigations," commented GL.

Manufacturers of all turbine types which have suffered the problem of edgewise vibrations recommend fitting a sensor device which stops a wind turbine before the vibrations lead to damaged components. All TW 600e turbines have been fitted with such a sensor. But in principle the sensor solution is far from ideal on any turbine, says GL's Christoph Brokopf. "When winds were strong in February, turbines equipped with these sensors were halted up to 80 times. No turbine is designed to stop as often as that. It causes considerable wear on the components and brakes," he says, though without reference to the make of turbine.

New models

In the meantime, Tacke Windenergie, now part of US energy giant Enron, launched two new turbine models at the Hannover Industry Trade Fair in April. These are the TW 600a, an adapted version of its 600 kW model, and a 1.5 MW turbine optimised for inland use. The nacelle of the new Tacke 600 kW was displayed on the Enron Wind Power stand alongside the Zond 750 kW nacelle from California. The TW 600a has been developed for export and is fitted with aerodynamic brakes, says Partmann.

The inland version of the Tacke 1.5 MW has a 70.5 metre rotor and 85 metre tower. The glass fibre blades for this machine are supplied by LM Aero Construct, LM Glasfiber's German division headed by Walter Keller. A prototype will go up at the DEWI test field in October and 12 of the model are to be installed at two sites in Schleswig Holstein in the first half of next year. Two wind farms using the 1.5 MWs, as the inland model is known, are also planned in Saxony, one of 26 machines and the other of six. Meanwhile, production of the standard TW 1.5 MW continues at one a week, though will be increased to about seven a month from July, says Tacke.

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