The onshore and offshore wind market is growing rapidly. Maintenance costs of wind energy systems are still high. Business operators are demanding solutions to reduce those costs. To address these technological challenges, an endurance test bench has been developed, reproducing the kinematics of a wind turbine on a reduced scale. This test bench was designed to create a progressive natural degradation of the main mechanical components of the drive train. Several sensors have been installed (vibration, currents, voltage, speed, temperature, forces, torques). During endurance testing, time data were recorded and analyzed, in order to determine the most effective methods for the detection of defects and to estimate the remaining life of the components. As an example, a focus on results on wind turbine main bearing monitoring is presented. Methods of detection of bearing defects are known and proven, but may not work applied to slow speed shaft.