Submitted to: American Society of Mechanical Engineers
Publication Type: Proceedings
Publication Acceptance Date: January 11, 1999
Publication Date: N/A
Interpretive Summary: Most small (10 kW and below) wind turbines turn out of the wind (furl) at high wind speeds similar to windmills. Furling prevents the wind turbine or windmill from exceeding the structural design limits of the machine. A 10 kW wind turbine being used for water pumping was almost completely destroyed due to furling at too high a wind speed at the USDA research center in Bushland, TX on Jan. 17, 1996. Furling was investigated on two smaller wind turbines (0.85 kW and 1.5 kW) to determine if simple changes could be made to these smaller wind turbines which would lower the furling wind speed and also be incorporated in a redesign of the 10 kW wind turbine. Increasing the rotor diameter on both of these smaller wind turbines resulted in decreasing the furling wind speed. Adding an electrical dumpload to the 0.85 kW wind turbine also improved the way this wind turbine furled for water pumping. Wind turbines can be used to produce electricity for a variety of uses: water pumping, battery charging supplying electricity to a household or to the utility via an inverter. A furling wind speed for one use may be satisfactory, but too high for another use. This is the case for the 10 kW wind turbine which furls satisfactorily when used with an inverter for generating electricity for a household or the utility, but furls at too high a wind speed for water pumping.
Technical Abstract: Most small wind turbines (10 kW and below) furl (aerodynamic/mechanical ability of wind turbine to turn out of the wind) for overspeed protection. Overspeed protection afforded by this furling action protects the rotor and other system components from being stressed beyond the limits for which they were designed. Testing wind turbines that furl has been performed by the USDA-Agricultural Research Service, Bushland, TX, since 1988. One 10 k wind turbine being tested came close to destruction when a guy cable attachment failed due to excessive vibration. The excessive vibration was caused by the high wind speed necessary to cause the turbine to furl. In November 1997 experimental testing was started on two smaller wind turbines (rated at 0.85 kW and 1.5 kW) to analyze and investigate ways of altering the furling wind speed which could be incorporated in a redesign of the 10 kW wind turbine. These changes involved changing the rotor diameter, the edirection of rotor rotation, and wind turbine electrical load. Increasing the rotor diameter by about 20% resulted in a decrease in furling wind speed of 4 to 5 m/s for the 0.85 kW wind turbine and 2 to 3 m/s for the 1.5 kW wind turbine. Changing the rotor rotation direction gave different results for the two wind turbines, but the larger tilt angle of the 10 kW wind turbine rotor axis may make changing the rotor rotation direction more effective. Applying the electrical load at a lower frequency with a smart controller on the 0.85 kW wind turbine resulted in a delay in furling of at least 4 m/s.