Experimental investigation of drivetrain resistance applied to small wind turbines

Abstract

Drivetrain resistance of wind turbines is still challenging, since determining static and dynamic frictional torque is rather complex. Hence, the main motivation of this work is to experimentally investigate resisting torques of a drivetrain typically found in small wind turbines. Measurements are carried out using a bench setup comprising torque sensor, rpm encoder, generator and electrical motor. For further evaluation, an approach combining Newton’s second law and blade element theory to assess the turbine behavior is employed, which is able to estimate the minimal wind velocity to start electrical generation, as well as the rated velocity of a small wind turbine. A theoretical expression for the friction torque is also demonstrated. An extension of SKF and Palmgren models are used to verify the friction torque on the bearings, which are often the main contributors to resistance in the turbine drivetrain. Assessments using a small wind turbine with 4 blades and 1.3 m diameter is performed to show the effect of the drivetrain resistance, in which its rotational speed changes according to the friction torque, yielding a more realistic response when the generator is loaded and unloaded.