Influences on torque measurement in nacelle test benches and their effect on the measurement uncertainty and consequences of a torque calibration

Torque measurement in the MN·m range is important in nacelle test benches, as it constitutes the primary value for the efficiency determination of wind turbine drive trains. However, no traceable measurement is possible above 1.1 MN·m. At the moment, alternatives to direct torque measurement in the MN·m range are, therefore, used. Several of these torque measurement methods are presented and discussed in this paper with respect to traceability and measurement uncertainty. It was found that these methods cannot fully substitute direct measurements. Therefore, detailed recommendations for a torque calibration procedure based on the specific conditions in nacelle test benches (such as rotation and additional mechanical loads) are given so as to enable the traceability of torque measurement using a torque transfer standard.