PO069

A Study to Demonstrate the Enhancement of Next Generation Drivetrains by a Composite Low-Speed Coupling

Alexander Kari 1, Christof Sigle1, Ralf Schelenz2, Jörg Berroth2, Paul Kunzemann2, Freia Harzendorf2
1Geislinger GmbH, Hallwang, Salzburg, Austria, 2Center for Wind Power Drives, Campus-Boulevard 61, Germany

Abstract

Driving energy cost down and increasing the reliability of wind turbines has been in the focus for many years. Non-torque loads were identified as a major root cause for deficient drivetrain reliability. Advances in design and material of the drivetrain and its components resulted in improvements of drivetrain reliability, particularly in the 2-3 MW class. But with increasing size of drivetrain structures of recent and future offshore turbines, non-torque loads and its impact on drivetrain deficiency becomes more important than ever. Using a low-speed coupling in wind drivetrains - a flexible coupling between the rotor and the gearbox absorbing non-torque-loads, whereas the gearbox is mounted rigidly to the main frame - is a rather new approach. This paper will show how a flexible coupling, made of advanced composite material, efficiently reduces non-torque loads without adding unnecessary complexity to the drivetrain and maintaining the tower head mass. For proper quantification of its effect, results of a multi-body simulation of a real drivetrain, considering specific wind load cases with and without a flexible coupling, will be presented. A summary of a commercial study will show the enhancement of the drivetrain architecture of this concept and illustrate the saving potential on capital expenditure and operational cost.

Method

To quantify the effect on load reduction and dynamic behaviour, a comparison of two identical drivetrains, one with and one without a flexible coupling, considering specific wind load cases is necessary. To realize this to be done, Geislinger teamed up with the Center for Wind Power Drives (CWD), a department of the RWTH Aachen University. Their generic 6 DOF wind turbine models are suitable to investigate the influence of new or modified drivetrain components on load and dynamics of the wind turbine. A state-of-the-art generic 6 MW offshore model with a three-stepped gearbox and hydraulic torque support was taken as a reference model. A composite coupling with its effective stiffness and damping values, integrated into the model, allowed a direct comparison to the reference model.

Results

This paper will show how a flexible coupling, made of advanced composites, efficiently reduces non-torque loads and enhances the dynamic system behaviour. The weight-saving design does not add unnecessary complexity to the drivetrain, is fatigue resistant and fully maintenance-free. Selected simulation results will illustrate a direct comparison of defined cut loads of both models considering all typical load cases, also by applying statistical methods such as LDD and rain flow counting. This allows facilitate determine the coupling's impressive influence on load reduction and on the dynamic behaviour of the drivetrain. A commercial side study, also performed by the CWD, will demonstrate the savings in capital expenditure around the area of the gearbox (such as reduction in size, saving of other components, higher degree of integration).

Conclusions

A composite low-speed coupling allows to mount the gearbox rigidly to the main frame by absorbing virtually all non-torque loads which are unnecessary stressing and fatiguing gearbox components. This technology not only possesses the ability to explicitly reduce gearbox peak loads and fatigue, but also to reduce size, weight and cost of the gearbox. From another perspective, it prevents the gearbox from growing linear with increased nominal power and allows comparatively compact and cost effective gearboxes for future offshore wind turbines. Moreover, this paper will show how the concept makes highly integrated drivetrains possible, also for 6+ MW offshore wind turbines, further simplifying and optimizing the drivetrain in terms of size and cost reduction of the gearbox and other drivetrain components.

Objectives

Visualize the load relieving effect on the gearbox and discover the vast enhancement of the dynamic behaviour of the whole drivetrain, particularly under severe conditions.

Describe the impact of a low-speed coupling on the drivetrain architecture and its potential to reduce size and cost of the gearbox.

Detect the opportunity in enabling highly integrated drivetrain architectures and the chance of a virtual risk-free upscaling of drivetrains for the next generation of offshore wind turbines.

Estimate the potential improvements in reliability, capacity factor and operational cost compared to a state-of-the-art drivetrain architecture.