Dennis Bosse

Robustness Test for Wind Turbine Gearbox Bearings

This paper introduces an innovative approach for the creation of the robustness test against specific failures of the planetary and HSS bearings (e.g. classical fatigue, smearing, micro-pitting, and lip fractures) in the wind turbine gearboxes. The introduced Bearing Robustness Test (BRT) considers the system-dependent characteristics (e.g. drive train design, interaction between components, assembly process, lubricant aging) and real dynamic load conditions, frequencies and sequence. The creation of the BRT is based on field and simulation data. The core element is the simulative approach for the determination of the relation between external wind and grid loads on the one side and local loads of the bearing on the other side. BRT aims the mapping of the most critical, but real, field load situations in the bearing test rig. By means of the BRT it is possible to evaluate the robustness of bearing against specific field conditions in the early stage of the product cycle and consequently to enhance the quality and to reduce the failure rate of the bearing. 1. Motivation and Objectives The cost-efficiency of the wind turbines is reduced by the frequent failures of the main gearboxes. The main gearbox is responsible for nearly 60 % of the downtime of the wind turbine, see Figure 1. This fact is caused by a fluctuating and dynamic wind and grid loads, dynamic interaction between drive train components as well as the demand for high power density of the gearbox components [1]. Therefore, the rolling contact bearings are the most critical component of the main gearbox. They contribute to over 67 % of main gearbox failures according to the current research, see Figure 1. The planetary and high-speed shaft (HSS) bearings failures cause high reparation, replacement and service costs [3]. Bearing testing methods within the product development process could contribute to more reliable and robust gearbox bearings and thereby increase the availability of the wind turbines. Nowadays, the existing testing methods cannot completely simulate the real elastic surroundings and reproduce the complex load situation on the bearing as well as the complex interaction between the gearbox components. Consequently, it is difficult to reproduce specific wind turbine bearing failures in a realistic way [4]. To solve this challenge, a diversified consortium of a complete product value chain (bearing, gearbox and wind turbine manufacturer)1 under the lead management of Chair for Wind Power Drives (CWD) got together to develop a new bearing test rig designs (a planetary 1 Schaeffler, SKF, Timken, NTN, Siemens Winergy, ZF Wind Power, Eickhoff, Vestas, Nordex, Senvion Figure 1. Causes for wind turbine downtime. 3% 3% 8% 2% 25%

Friction as a major uncertainty factor on torque measurement in wind turbine test benches

Most of the existing multi-MW nacelle test benches (NTB) measure the MNm torque before load application system (LAS) to reduce the cross-talk effect of the multi-component forces and bending moments on torque measurement. This means that the friction torque of the LAS reduces the applied torque and consequently directly determines the input torque on the device under test (DUT). Therefore, the knowledge of the friction torque is necessary for the precise experimental investigations (e.g. efficiency measurement). At the beginning of this paper, a Computational Fluid Dynamics (CFD) simulation method for the determination of the friction torque of the LAS, which is suspended by hydrostatical plain bearings, is introduced. Subsequently, this method is validated with experimental results. Afterwards the friction torque of the LAS is quantified under different operation conditions (e.g. variation of rotational speed, multi-component load and temperature). Finally, the influence of the quantified friction torque on the uncertainty of the MNm measurement is compiled.

A Sensitivity analysis of planetary- and high speed shaft bearing loads in wind turbines

Long downtime periods burden the economic efficiency of wind turbines (WT). 60% of all downtime periods are caused by gearbox failures and most of them are caused by bearing outages [1]. Planetary and high speed shaft bearing failures are responsible for more than 70% of these bearing outages [2]. The causes for these failures are frequently dynamical mechanical loads at the bearing stages. This shows that the dynamic loads at these bearing stages are yet not sufficiently well known. To analyse the influences on bearing loads at the planetary and high speed shaft stage, a sensitivity analysis with varying loads at the hubflange for pitch-, yaw-, drive-torque and thrust is done. As additional factors different bearing clearances and shaft stiffnesses were considered. The results show, that the drive torque at the hub flange has the main influence on value, amplitude and

Feasibility of large-scale calorimetric efficiency measurement for wind turbine generator drivetrains

In the course of the global energy turnaround, the importance of wind energy is increasing continuously. For making wind energy more competitive with fossil energy, reducing the costs is an important measure. One way to reach this goal is to improve the efficiency. As the major potentials have already been exploited, improvements in the efficiency are made in small steps. One of the main preconditions for enabling these development activities is the sufficiently accurate measurement of the efficiency. This paper presents a method for measuring the efficiency of geared wind turbine generator drivetrains with errors below 0.5% by directly quantifying the power losses. The presented method is novel for wind turbines in the multi- MW-class.