PROTOTYPE FAILS

Investigating: Until a full report is complete, Danish firm Bonus has little idea why its 750 kW prototype failed in winds of 16-17 m/s on October 17. "The accident happened when the rotor speeded up," says technical director Henrik Stiesdal. "The turbine has two independent safety systems -- separate pitch control of each blade and a mechanical brake. At first sight it looks as if the pitch mechanism on each blade failed at the same time." An investigation group of staff from Bonus, the wind turbine test station at Risø, Det Norske Veritas and Vestkraft utility, the owner, expects to make its first report soon. The turbine, which has a 50 metre rotor, is sited at Tjærborg, alongside Nordtank's 1.5 MW prototype and utility Elsam's 2 MW experimental unit. Installed in 1994 the Bonus unit operates with both pitch and stall control.