In the rough operation of a wind turbine, constantly changing forces from all directions generate dynamic 5DOF loads on the turbine drive shaft. The total power of this stormy environment is given in test rig operation by the hydraulic load application unit (LAU),. To generate these forces and bending moments, RENK favors a hydrostatic disc for load transfer (D-LAU). This hydrostatic disc is directly connected to the main shaft of the turbine and is driven by the multi-motor drive system. Hydraulic actuators transmit the multi-axial loads to the rotating disk via plain bearing elements. This design only introduces minimal interference into the overall system and thus meets the highest demands in terms of measurement and control accuracy.

The plain bearing used has a calculated infinite service life and, unlike rolling bearings, never needs to be replaced - even under the highly demanding dynamic load collectives of a nacelle test rig.

In dynamic operation, the measuring accuracy from the test specimen to the hydraulic actuators exhibits considerable losses due to the long distance. For this reason, RENK has developed a multi-channel measuring flange for very large loads; which is positioned directly at the interface to the main shaft of the test specimen. With this measuring flange, the applied loads can be recorded in real time without loss during rotation and taken into account in the test rig control. This multi-axial measuring flange, in conjunction with the virtually lossless hydrostatic loading device, enables unique measuring and control accuracies.