A systems engineering analysis of three‐point and four‐point wind turbine drivetrain configurations

Abstract

This study compares the impact of drivetrain configuration on the mass and capital cost of a series of wind turbines ranging from 1.5 MW to 5.0 MW power ratings for both land-based and offshore applications. The analysis is performed with a new physics-based drivetrain analysis and sizing tool, Drive Systems Engineering (DriveSE), which is part of the Wind-Plant Integrated System Design & Engineering Model. DriveSE uses physics-based relationships to size all major drivetrain components according to given rotor loads simulated based on International Electrotechnical Commission design load cases. The model's sensitivity to input loads that contain a high degree of variability was analyzed. Aeroelastic simulations are used to calculate the rotor forces and moments imposed on the drivetrain for each turbine design. DriveSE is then used to size all of the major drivetrain components for each turbine for both three-point and four-point configurations. The simulation results quantify the trade-offs in mass and component costs for the different configurations. On average, a 16.7% decrease in total nacelle mass can be achieved when using a three-point drivetrain configuration, resulting in a 3.5% reduction in turbine capital cost. This analysis is driven by extreme loads and does not consider fatigue. Thus, the effects of configuration choices on reliability and serviceability are not captured. However, a first order estimate of the sizing, dimensioning and costing of major drivetrain components are made which can be used in larger system studies which consider trade-offs between subsystems such as the rotor, drivetrain and tower. INTRODUCTIONThree-point and four-point suspensions, which refer to wind turbine drivetrain configurations with either one or two main bearings, respectively, are the most common wind turbine drivetrain architectures. In the three-point suspension configuration, the rotor is rigidly connected to the main shaft, which is supported by a single main bearing near the rotor. A shrink disk typically connects the downwind side of the shaft to the low-speed stage of the gearbox. The gearbox is supported by two torque arms that are connected to the bedplate elastically. These two torque arms, along with the single main bearing, provide a total of three points of support. Commercial wind turbines that utilize this configuration include the General Electric GE 1.5 MW, Siemens SWT108 2.3 MW, Nordex N117 2.4 MW and Vestas V112 3 MW. 1 Four-point suspension configurations, sometimes referred as two-main-bearing suspension configuration, place an additional main bearing near the down-wind side of the main shaft with the intent of isolating any non-torque rotor loads upwind of the gearbox. Non-torque rotor loads are the non-torsional loads transmitted from the rotor blades to the drivetrain. These non-torque loads can affect gearbox reliability significantly by causing uneven loads among planetary gears and reducing bearing life. 2 The design protects the gearbox from non-torque loads but, at the same time, suc...

Wind turbine main‐bearing loading and wind field characteristics

“…While the current work considers possible differences in loading and related implications concerning failure rates for DMB and SMB configurations, there are other dimensions to bearing design and selection, such as cost and ease of servicing or replacement, which are factored in when design decisions are made. For example, a study relating drivetrain configuration to capital cost found that a SMB configuration can result in a reduction in turbine capital cost of up to 3.5% compared with the DMB setup. Therefore, while hopefully illuminating in terms of understanding differing failure rates in the reported figures, the load analysis considered here should not be deemed conclusive in terms of overall optimum bearing selection.…”

A review of wind turbine main bearings: design, operation, modelling, damage mechanisms and fault detection

“…Inherent wind field structure can also deviate significantly from the standard representations outlined above. Examples of this include veered flow (a shear-like effect where wind direction changes with height rather than wind speed), coherent turbulence phenomena (Kelley et al, 2005) and lowlevel jets (Gutierrez et al, 2014(Gutierrez et al, , 2017. As with wind turbine wakes, the development of theory to model and relate these phenomena to turbine loading and performance is ongoing.…”

“…The most common drivetrain configurations for geared turbines are those with three-point or four-point suspensions, referring to turbines with either a single-main-bearing (SMB) or double-main-bearing (DMB) setup respectively (Guo et al, 2016). Examples of these two configurations are shown in Fig.…”

“…A SMB layout requires gearbox trunnions to react loads at the gearbox end of the LSS, and so in combination there are three points of support. This setup has been used in commercial wind turbines by GE, Siemens (prior to becoming Siemens Gamesa), Nordex and Vestas for machines rated at between 1.5 and 3 MW (Guo et al, 2016). For the DMB layout, a second bearing is placed near the gearbox end of the LSS in an attempt to react nontorque loads before they reach the gearbox.…”

Comparison of Planetary Bearing Load-Sharing Characteristics in Wind Turbine Gearboxes

“…configuration transfers torque as well as rotor moments through the gearbox, which is an important design consideration (Guo et al, 2017). The GRC gearbox design has a single input planetary stage followed by two parallel-shaft stages.…”