Experimental tests of wind turbine main shaft motion on a laboratory test rig

Abstract

This paper introduces research and discusses findings dealing with failure modes of gearboxes in wind turbines. These gearboxes fail in general after five years which is far below the expected design life of twenty years of a wind turbine. The research is taking a more holistic approach towards finding typical behaviour of the main shaft taking the transient nature of the wind into consideration. In this research, a small scale wind turbine test rig has been designed and manufactured with displacement sensors installed to observe the displacement of the main shaft at specific points, namely the main bearing locations of the forward framework of a wind turbine nacelle, where the main shaft is installed. The experimental data measured from the test rig is being analysed with common beam bending, statistical and fatigue theories to draw conclusions for long term loading in service. Aspects of the turbulent nature of the wind driving the wind turbine have been taken into consideration as being part of the aerodynamic loading onto the rotor and eventually the gearbox, transmitted through the main shaft. The purpose of the test rig at this stage is to obtain a quantitative insight into the motion of the main shaft. The deliberately chosen softer aluminum material and the more slender geometry for the components should provide exaggerated displacements which help to make motion and deformations more obvious. At this point, no resemblance to real size wind turbines has been established.