Multi-physical investigation of innovative WTG drivetrain concepts using the example of the Winergy “HybridDrive”

Introduction

In current drivetrains of onshore wind turbine generators (WTG), there is no prevailing consistent concept. As there is high potential for innovations, manufacturers continuously look for improvements with respect to reliability, maintainability, and profitability. With the HybridDrive concept (first taken into operation in 2013), Winergy has advanced one step further in compact modular design of an electromechanical drivetrain. The HybridDrive consists of a two-stage planetary gearbox and a mid-speed permanent-magnet synchronous generator within a single housing assembly. By testing this multi-physical system on the 4 MW test bench at the Center for Wind Power Drives (CWD) in Aachen, insights into the mechanical and electrical dynamics have been gained. This paper presents chosen approaches and results.

Approach

On the test bench, the HybridDrive was operated under conditions close to reality. The original mounting concept was retained: Due to 45 rubber bushings distributed equally over the circumference of the torque arm, the displacement of the gearbox is decoupled from the deformation of the supporting structure. In combination with 30 further elastomeric elements in the gearbox input flange, a double-swivel mounting is facilitated. At the drive side, dynamic loads in 6 degrees of freedom were applied to the device under test by an electrical direct drive and a hydraulic non-torque loading unit (NTL). In order to evaluate Winergy’s concept, reactions to local loads were investigated as well as the behaviour of the overall system. This comprises measuring strain in tooth roots, power distribution within the first planetary gear stage, relative displacement at the gearbox mounting, and system efficiency.

Main body of abstract

The quality of the double-swivel mounting is verified by the displacement values between the torque arm and the supporting structure. As the displacement is measured at three positions in axial direction, the tumbling motion of the gearbox housing can be calculated. Results show that the axial deformation of the rubber bushings caused by additionally applied lateral forces and bending moments decreases with increasing drive torque. Consequently, the general rigidity of the double-swivel mounting is related to the input torque. At high power levels, the increased rigidity leads to an increase in unintended forces at the gearbox input flange.
Within the first planetary stage of the gearbox the unintended forces influence the load distribution across the face width of the single gears. Strain measurements in the tooth roots of the sun gears and ring gears in both planetary stages have been carried through in order to verify this interaction. Furthermore, the measured strains allow for conclusions concerning the power distribution on the four planets of the first gear stage. With increasing torque, variations caused by elastic deformations can be observed.
Measuring the efficiency of the electromechanical drivetrain was another aim of analysis. Efficiency measurements of the generator have already been described in previous publications. These investigations have now been extended to the complete system. After an evaluation of several methods for measuring the efficiency of heavy-duty drive systems, a calorimetric procedure was specified. Due to the general advantages of this method, high accuracy in the efficiency values could be reached even in the present system scale.


Conclusion

The tests performed with the HybridDrive drivetrain demonstrate the versatility of investigations with different depths of monitoring, which can be carried out on a single test bench. Not least because of arbitrary and reproducible operating conditions, new insights can quickly be fed into the development process in advance to field testing.


Learning objectives
Testing a complete WTG nacelle is not possible in an early state of the development process. As components like the HybridDrive are dependent on the nacelle, there is a need for testing procedures to verify their operability in their intended environment. Planned research activities will show, how and to which extent the environment of the DUT has to be considered in order to receive results which are highly relevant for a reliable operation of the component in the turbine.