A study of mechanical torque measurement on the wind turbine drive train-ways and feasibilities

The signal of the drive train mechanical torque can be a very informative input for new technologies on the wind turbine, helping further reducing the cost of energy. However, measuring the mechanical torque is not an easy task even during a test campaign on a prototype. In case of the long-term measurement for operational purpose of use on the turbine, it is often considered as technically and economically not feasible. This paper discusses possible ways of the torque measurement and presents a test campaign where two different methods of torque measurement are conducted. One of the methods measures the shear strain signal using strain gauges at one section of the turbine main shaft. The other method measures the torsional deformation between two positions of the drive train, with an incremental encoder measuring the angular position of the drive train at each position. The tests are conducted on an 8-MW wind turbine drive train under tests on the nacelle test bench "DyNaLab" of Fraunhofer IWES. During the tests, different load steps of torque and other load components are applied to the drive train. The measurement results from both measuring methods are presented and analysed. In the end, technical and economical feasibilities are discussed for both methods of torque measurement; some suggestions are also given respectively.