Calibration of torque measurement under constant rotation in a wind turbine test bench

To determine the efficiency of multi-MW wind turbines, the torque measurement in wind turbine test benches has to be performed with an accuracy better than 0.2 %. To this end, the torque measurement has to be traced to national standards in the MN m range. This can be done by using a novel torque transfer standard in combination with a newly developed torque calibration procedure under constant rotation, which are both presented and discussed in this paper. The calibration procedure was performed on a 4 MW wind turbine test bench and the evaluation of the calibration result, including a measurement uncertainty, is explained in detail.