An effective method of determining the drive-train efficiency of wind turbines with high accuracy

Measurement of efficiency under various load conditions is an important prerequisite for the validation of wind turbine drive train systems. Current measurement methods rely highly on the accuracy of the mechanical torque measurement, which is substantially limited by the high level of torque as well as the available calibration capacity. This paper proposes a new method of test and measurement procedures, aiming to substantially reduce the dependency of the efficiency accuracy on the torque and electrical power measurement. Instead of measuring the efficiency directly, the new method focuses on measuring the loss of power and in this way reduces the uncertainty of the determined efficiency. At rated power, an uncertainty lower than 0.5 % is considered as achievable. The efficiency uncertainty is analysed in detail in the paper with considerations of different sources of measurement uncertainties and their contributions. An example of the uncertainty calculation with typical parameters is presented as a demonstration. The study shows that the new method can effectively reduce the effect of the torque (as well as the electrical power) uncertainty on the overall uncertainty of the determined efficiency, and therefore achieve a better accuracy despite of the unfavourable accuracy of the torque and electrical power measurement. Finally, experimental tests have been performed on a scaled dynamometer test bench, where the efficiencies at different operation points are determined with the new method. The efficiency results as well as their uncertainties are presented in the paper.